Organocatalytic, diastereo- and enantioselective synthesis of nonsymmetric cis -stilbene diamines: A platform for the preparation of single-enantiomer cis -imidazolines for protein-protein inhibition

Article abstract of DOI:10.1021/jo501003r

The finding by scientists at Hoffmann-La Roche that cis-imidazolines could disrupt the protein-protein interaction between p53 and MDM2, thereby inducing apoptosis in cancer cells, raised considerable interest in this scaffold over the past decade. Initial routes to these small molecules (i.e., Nutlin-3) provided only the racemic form, with enantiomers being enriched by chromatographic separation using high-pressure liquid chromatography (HPLC) and a chiral stationary phase. Reported here is the first application of an enantioselective aza-Henry approach to nonsymmetric cis-stilbene diamines and cis-imidazolines. Two novel mono(amidine) organocatalysts (MAM) were discovered to provide high levels of enantioselection (>95% ee) across a broad range of substrate combinations. Furthermore, the versatility of the aza-Henry strategy for preparing nonsymmetric cis-imidazolines is illustrated by a comparison of the roles of aryl nitromethane and aryl aldimine in the key step, which revealed unique substrate electronic effects providing direction for aza-Henry substrate-catalyst matching. This method was used to prepare highly substituted cis-4,5-diaryl imidazolines that project unique aromatic rings, and these were evaluated for MDM2-p53 inhibition in a fluorescence polarization assay. The diversification of access to cis-stilbene diamine-derived imidazolines provided by this platform should streamline their further development as chemical tools for disrupting protein-protein interactions.

Full text of DOI:10.1021/jo501003r

Article
pubs.acs.org/joc
Open Access on 07/14/2015
Organocatalytic, Diastereo- and Enantioselective Synthesis of
Nonsymmetric cis-Stilbene Diamines: A Platform for the Preparation
of Single-Enantiomer cis-Imidazolines for Protein−Protein Inhibition
Brandon A. Vara,† Anand Mayasundari,‡ John C. Tellis,† Michael W. Danneman,† Vanessa Arredondo,†
Tyler A. Davis,† Jaeki Min,‡ Kristin Finch,‡ R. Kiplin Guy,*,‡ and Jeffrey N. Johnston*,†
†Department of Chemistry & Vanderbilt Institute of Chemical Biology, Vanderbilt University, 7330 Stevenson Center, Nashville,
Tennessee 37235, United States
‡Department of Chemical Biology and Therapeutics, St. Jude Children’s Research Hospital, 262 Danny Thomas Place, Memphis,
Tennessee 38105, United States
S
* Supporting Information
ABSTRACT: The finding by scientists at Hoffmann-La Roche that
cis-imidazolines could disrupt the protein−protein interaction
between p53 and MDM2, thereby inducing apoptosis in cancer
cells, raised considerable interest in this scaffold over the past decade.
Initial routes to these small molecules (i.e., Nutlin-3) provided only
the racemic form, with enantiomers being enriched by chromato-
graphic separation using high-pressure liquid chromatography
(HPLC) and a chiral stationary phase. Reported here is the first
application of an enantioselective aza-Henry approach to non-
symmetric cis-stilbene diamines and cis-imidazolines. Two novel
mono(amidine) organocatalysts (MAM) were discovered to provide
high levels of enantioselection (>95% ee) across a broad range of
substrate combinations. Furthermore, the versatility of the aza-Henry
strategy for preparing nonsymmetric cis-imidazolines is illustrated by a comparison of the roles of aryl nitromethane and aryl
aldimine in the key step, which revealed unique substrate electronic effects providing direction for aza-Henry substrate−catalyst
matching. This method was used to prepare highly substituted cis-4,5-diaryl imidazolines that project unique aromatic rings, and
these were evaluated for MDM2-p53 inhibition in a fluorescence polarization assay. The diversification of access to cis-stilbene
diamine-derived imidazolines provided by this platform should streamline their further development as chemical tools for
disrupting protein−protein interactions.
MDM2, even though the p53 gene is either deleted or mutated
in approximately 50% of all human cancers.7−9 Additionally,
since MDM2 is overexpressed in many types of cancer and
functions as a key negative regulator of wild-type p53, the Nutlins
have shown promise as anticancer therapeutics. Hoffmann-La
Roche (HLR) was the first to advance a Nutlin analogue
(RG7112) into clinical trials for solid and hematological tumors.10,11
An MDM2 homologueMDMX or MDM4is similarly overex-
pressed in nearly one-fifth of lung cancers, breast cancers, and
retinoblastomas12,13 and was most recently found to be overex-
pressed in ∼65% of human melanomas.14 Recent reports have since
validated MDMX as an additional and valuable therapeutic
target.15−17 The chemistry discussed hereafter has enabled the
facile synthesis of a number of enantioenriched cis-imidazolines
modeled after (−)-Nutlin that were evaluated for MDM2-p53
inhibition using a previously reported fluorescence polarization
competition assay for p53 peptide binding to MDM2.18
INTRODUCTION
■
Initially discovered by high-throughput screening at Hoffman-La
Roche (HLR) in 2004, the Nutlins are cis-imidazoline small
molecules that inhibit the MDM2-p53 protein−protein
interaction (PPI).1 The Nutlins have been widely used to
study the consequences of inducing the activity of the tumor
suppressor p53 when it is suppressed by MDM2 in cancer cells.2
To date, HLR has continued to pursue cancer drug development
with the series.3 The most potent member (and enantiomer) in
the original Nutlin family, (−)-Nutlin-3 (1, Chart 1), or Nutlin-
3a, is able to selectively disrupt the binding of MDM2 and p53 by
mimicking the side chains of key hydrophobic p53 amino acid
residues in the MDM2 binding motif.1 This orthosteric binding
releases p53 from its heterodimer complex with MDM2, leading
to cell cycle arrest and apoptosis. Since the initial discovery of the
Nutlins, a host of structurally different MDM2-p53 inhibitors
that function as p53 mimetics have been reported.4 These small
molecules have received much attention from academia and
industry in the past decade, since the function of wild-type (WT)
p53 is inactivated by overexpression5 or amplification6 of
Received: May 8, 2014
Published: July 14, 2014
© 2014 American Chemical Society
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cis-imidazolines bearing unique aromatic rings at C4 and C5, and
yet access to these small molecules may eventually lead to
selective and potent inhibitors of protein−protein interactions.
Application of the aza-Henry approach to this problem was
not without potential complication. While convergence in the
imidazoline synthesis would be well-served (top equation in
Figure 1), the levels of enantioselectivity can be attenuated by
electronic effects. These challenges are often overcome by
reagent (catalyst) modification while maintaining a high level of
catalyst activity. When successful, this typically provides the most
general solution.
Chart 1. Nutlin Family of p53/MDM2 Inhibitors
Separately, the aza-Henry construction of unsymmetrical cis-
stilbene diamines offered a strategic question to be examined in
conjunction with tactical catalyst development. As outlined in
Figure 1, a single enantiomer of imidazoline 6 bearing unique
aromatic substituents can be prepared in two ways using this
strategy, on the basis of catalyst antipodes and the roles of the
nitroalkane and imine (cf. top and bottom equations in Figure 1).
The studies reported here detail our work to (1) the
identification of a new class of mono(amidine) organocatalyst
(MAM) that provides high levels of enantioselection in the aza-
Henry addition involving diverse combinations of aryl nitro-
methane donors and imine acceptors, (2) the implementation
and evaluation of parallel pathways to cis-imidazolines 6, and (3)
the synthesis and biological evaluation of novel cis-imidazoline
MDM2 inhibitors rationally designed from (−)-Nutlin-3. As a
result, highly enantioenriched cis-imidazolines bearing either
identical or differentiated aryl substituents at C4 and C5 are now
more generally accessible and can be applied to therapeutically
valuable small molecules.
Scheme 1. Overview of the Enantioselective Aza-Henry
Approach to cis-Imidazolines
RESULTS AND DISCUSSION
We recently reported the first asymmetric synthesis of
(−)-Nutlin-3 (1, Scheme 1).19,20 This required the development
of a diastereo- and enantioselective aza-Henry reaction with an
aryl nitromethane (3a),21 a pronucleophile used on only two
prior occasions but with low levels of selectivity in this context.22
The β-amino nitroalkane product (4aa) was transformed in five
linear steps to (−)-Nutlin-3. Alternatives to prepare Nutlin-3
remain limited to (1) the HLR synthesis of ( )-Nutlin-312
followed by chromatographic separation of the enantiomers23,24
and (2) a promising enantioselective acylation of symmetric
cis-stilbene diamines reported recently by Seidel.25 Further
modifications to our preparation have reduced chromatographic
purification of intermediates to one, enabling the preparation of
(−)-Nutlin 3 on a multigram scale (>17 g/batch).20
■
We elected to first study the use of an electron-deficient aldimine
(2b) paired with a relatively unbiased aryl nitromethane (3a)
using a standard set of conditions (24 h at −20 °C). The Boc-
imine of 3-(trifluoromethoxy) benzaldehyde was prepared in
good yield using a standard procedure.27 Two of our most
reactive and selective catalysts were evaluated,19,20 and as in
previous studies, we hypothesized that the combination of a
Brønsted basic catalyst with a Brønsted acidic aryl nitromethane
would form a salt (e.g., 7·H+−CH(Ar)NO2) that can, in turn,
function as a bifunctional Brønsted acid/Brønsted base in the
reaction. First-generation Brønsted basic catalysts (S,S)-PBAM
(7) and (R,R)-8(MeO)PBAM (8) afforded the aza-Henry adduct
(ent-4ab and 4ab) in −52% and 61% ee, respectively. Although
the reactivity and diastereoselectivity were generally comparable
to those of past pyrrolidine bis(amidine) (PBAM) catalysts, the
enantioselectivity was diminished. In theory, this may be due to
The use of a diaza-Cope reaction by HLR provided access
to a large number of symmetrical cis-stilbene diamines.26 The
diaza-Cope reaction is less amenable to the preparation of
Figure 1. Parallel pathways to the same enantiomer of cis-imidazolines derived from nonsymmetric cis-stilbene diamines.
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combinations of amidine and amide functionalities projected
from the diamine backbone. The conceptual framework for this
modification was also rather different by comparison to previous
bis(amidine) modifications. Beginning from its free base form,
the catalyst would be expected to form a salt with the aryl
nitromethane at the amidine (eq 1, Figure 2), but the greatest
level of dual activation is expected to involve electrophile binding
to the polar ionic hydrogen bond concomitant with nitronate
counterion binding to the (amide) polar covalent hydrogen
bond. Figure 2 illustrates this conceptually, progressing from
substrates and catalyst in A to catalyst-bound product in D. The
initial activation event is catalyst deprotonation of the nitro-
alkane, but in this arrangement (B), the nitronate reactivity may
be attenuated by a strong ion pair and imine activation by an
amide N−H may be relatively weak. Exchange of the hydrogen
bond acceptors (Figure 2, C), however, leads to a more reactive
nitronate due to charge separation and increased activation of the
imine. An arrangement such as this might maximize the benefit of
drawing the counterion away from the electrophile binding site
while providing discrete directional control. Elements of this
approach overlap with developments in the field of anion binding
catalysis, particularly when the catalyst involves two polar
covalent hydrogen bond donors.28 Other catalyst systems use
not only a Brønsted basic catalyst but also a Brønsted base
additive (e.g., Et3N).29
Figure 2. Outline for activation of aryl nitromethane (nucleophile, Nu)
and imine (electrophile, E) by a bifunctional catalyst.
The Mono(AMidine) (MAM) catalysts in Scheme 2 were
prepared in five steps using an approach that mirrored our prepa-
ration of unsymmetrical bis(amidine) ligands in prior studies.30
Under reaction conditions identical with those used for 7 and 8,
(S,S)-PivMAM (ent-9) afforded the addition adduct in an im-
proved −87% ee and 5:1 dr (54% yield), while (S,S)-BenzMAM
(ent-10) afforded the adduct in −94% ee and 6:1 dr (62% yield).
A similar comparative analysis was made using aldimine 2a
in combination with a range of electronically diverse aryl
nitromethanes 3x, yielding adducts 4xa (Table 1). The aryl
the elevated temperature of the reaction (−20 °C in contrast
with −78 °C of past reactions) and/or intolerable steric
interactions with the catalyst.
As an alternative to an extensive exploration of the impact of
quinoline substituents on enantioselection,19 an effort that
afforded little improvement in this case, we reasoned that the
insensitivity of aryl nitromethane additions to added strong
acid (e.g., TfOH) might offer the opportunity to explore
a
Scheme 2. Catalyzed Aza-Henry Addition of p-Chloro Aryl Nitromethane to Aryl Boc-imines
a
Conditions: 1.1 equiv of nitroalkane in toluene (0.1 M). The diastereomeric ratio (dr) and enantiomeric excess (ee) were determined by chiral
b
HPLC. Using this enantiomeric diamine backbone, ent-4ab is formed, as expected.
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using 8 (Table 1, entries 1 and 2, respectively). High levels of
selectivity continued during the evaluation of a range of
electronically deficient (Table 1, entries 3−7) and electronically
neutral (Table 1, entry 8) aryl nitromethanes, providing the aza-
Henry adducts with excellent enantioselection (92−94% ee).
2-Fluoro-5-bromoaryl nitromethane (Table 1, entry 6) provided
an exception to the trend, however, as the bis(amidine) free base
Table 1. Aza-Henry Additions of Aryl Nitromethanes
to p-Chlorophenyl Boc-imine
a
8
of (MeO)PBAM (8) provided the aza-Henry adduct in the
highest ee in comparison to PivMAM (9) and BenzMAM (10).
The most electron rich case, 3,4-dimethoxyaryl nitromethane
(Table 1, entry 10), converted with lower enantioselectivity and
reaction rate, perhaps due to its diminished Brønsted acidity.
Dialing back the electronic effects to (mono)methoxyaryl
nitromethane 3i (Table 1, entry 11), however, reestablishes
good levels of stereocontrol (95% ee and >20:1 dr). Interestingly,
PivMAM (9) enhanced enantioselectivity for meta-substituted
arenes (Table 1, entries 4, 5, 8, and 9). For example, the adduct of
3-chloroaryl nitroalkane (Table 1, entry 5) was formed in 89% ee
with BenzMAM (10), in comparison to 93% ee when PivMAM
(9) (Table 1, entry 4) was employed.
The substrate scope for aryl Boc-imines (2x) was investigated
next (Table 2). The synthesis of aryl Boc-aldimines from
α-amido sulfones31 is well established, and a wide array of
aldimine substrates can be prepared.32 A range of aryl Boc-imines
was prepared for analysis, leading to β-amino nitroalkanes (4ax)
in very high enantio- and diastereoselectivity (up to 99% ee and
>200:1 dr; Table 2). Haloaryl (Table 2, entries 1−5, 7, 8, and 10),
electron-deficient imines (Table 2, entries 7−10), and electron-
neutral (Table 2, entry 6) and electron-rich imines (Table 2,
entries 11 and 12) were transformed to β-amino nitroalkanes in
uniformly good to excellent dr/ee and isolated yield.
The behaviors outlined in Table 2 suggest that electronic
variations to the aldimine affected stereoselection to a lesser
degree than that observed with aryl nitromethane donors. This
was more carefully investigated by examining each pairing of
aldimine (2) and aryl nitromethane (3) substrates to explore and
better gauge reactivity trends (Table 3). The arenes selected in
Table 3 contain a wide range of functionalities with the purpose
of maximizing diversity to a reasonable extent. Using a stan-
dard set of reaction conditions, aryl Boc-imines 2 and aryl
nitromethanes 3 were combined. Aryl Boc-imines 2j,k and their
nitroalkane counterparts 3d,h are notable challenges, as they
represent highly electron poor and rich substrates, respectively,
in the aza-Henry reaction. As was expected, the ee and dr values
observed for neutral and moderately electron deficient aryl
nitromethanes are uniformly high (Table 3, entries 1−4,
3a,b,f,c). The comparison of ent-4fh with 4cg, however, is an
exception to this trend. Under identical reaction conditions with
BenzMAM (10), 3-chloro nitroalkane (3c) behaves remarkably
better than its imine counterpart (2h) on reaction with the
3-methyl arene partner (99% ee, >20:1 dr by 1H NMR and 85%
ee, 8:1 dr, respectively). A few generalizations can be made from
the data generated as well. aza-Henry adducts where the electron-
poor 2-fluoro-5-bromo arene is employed as the nitroalkane
(3d) consistently resulted in low drpresumably due to the
increased α-hydrogen acidity in the product (up to 5:1 dr, 4dg).
Fortunately, the 2-fluoro-5-bromoaryl imine (2j) delivers
adducts with improved diastereoselectivity and enantioselectivity
in specific cases (4fj, 85% ee/40:1 dr, in comparison to 4dg, 68%
ee/5:1 dr). In the case of the 3,4-dimethoxyaryl substrate,
employing this electron-rich arene as the nitroalkane (3h)
proved unsatisfactory (up to 78% ee/20:1 dr, 4hg) in almost
every case. Gratifyingly, significantly higher ee and dr was
a
All reactions employed 1.1 equiv of nitroalkane in toluene (0.1 M)
b
at −20 °C with 24−36 h reaction time. Catalyst prepared from (R,R)-
cyclohexanediamine or (S,S)-cyclohexanediamine (denoted ent).
c
Diastereomeric ratio (dr) and enantiomeric excess (ee) determined
by chiral HPLC following vacuum filtration or silica column
d
chromatogaphy (see the Supporting Information). Isolated yields.
e
Reaction temperature: −78 °C.
nitromethanes were prepared from their corresponding and
commercially available benzaldehyde derivatives, and all were
successful feedstock for the aza-Henry reaction using represen-
tative conditions (5 mol % catalyst loading, −20 °C, toluene;
Table 1). We first examined MAM catalyst 10 efficacy with
4-chlorophenyl nitromethane and 4-chlorophenyl Boc-imine
(Table 1, entry 1), to compare the new catalyst directly to 8; the
resulting aza-Henry adduct 4aa can lead to (−)-Nutlin-3 (1).
BenzMAM (10) provided the adduct in 96% ee and 53:1 dr
at −20 °C, in comparison to 91% ee and 13:1 dr at −78 °C when
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a b
,
Table 2. Catalyzed Aza-Henry Addition of p-Chlorophenyl Nitromethane to Aryl Boc-imines: Scope using Catalysts 9 and 10
a
b
All reactions employed 1.1 equiv of nitroalkane in toluene (0.1 M) at −20 °C with 24−36 h reaction time. Catalyst prepared from (R,R)-
c
cyclohexanediamine or (S,S)-cyclohexanediamine (denoted ent). Diastereomeric ratio (dr) and enantiomeric excess (ee) were determined by chiral
HPLC following vacuum filtration or silica column chromatography (see the Supporting Information). Isolated yields.
d
observed when this arene was employed as the imine (up to 93%
ee/56:1 dr, 2k). To further illustrate the value of this observation,
entries 4hh and 4ck should be compared. In cases where the
adducts were generated in suboptimal ee and dr, switching
catalyst antipode and arene pairings proved beneficial in almost
all cases, using the tactic outlined in Figure 1. The 36 compounds
outlined in Table 3 represent a wide range of possibilities when
targeting symmetrical or unsymmetrical cis-stilbene diamines.
These experiments further demonstrate synthetic flexibility using
a pair of mono(amidine) (MAM) amide catalysts (9 and 10) to
access highly diastereo- and enantiomerically enriched aza-Henry
adducts.
Table 3 gives adducts that contain either an underlying symmetric
cis-stilbene diamine backbone (results along the diagonal from top
left to bottom right), or a nonsymmetric cis-stilbene diamine
backbone. The latter are constitutional isomers paired on either
side of the diagonal. This relationship was considered when
converting these intermediates to their derived cis-imidazolines
(cf. 5a,b → 6, Figure 1). If the two constitutional isomers in
Figure 1 are transformed into their derived cis-imidazolines using
identical procedures and reagents, the final imidazolines would be
enantiomeric at their C4 and C5 carbon centers (although overall
constitutionally isomeric cis-imidazolines). However, if the constitu-
tional isomers are formed using enantiomeric catalysts, and the order
of steps 2 (amide formation) and 4 (urea formation) is reversed, then
the same enantiomer of the cis-imidazoline will be formed, as outlined
in Figure 1. Additionally, the benefits of this method allow for direct
and predictable functionalization at a given nitrogen due to their
protected nature. Previous attempts at monoderivatization from
symmetric (meso) or nonsymmetrical stilbene diamines are notorious
for generating a mixture of mono- and disubstituted products.33 This
strategy was reduced to practice using the example in Scheme 3.
In the first case, p-chloro aldimine 2a was converted to 4ba
using (R,R)-BenzMAM (10) and p-bromoaryl nitromethane 3b.
This adduct was then converted to cis-imidazoline 11 using the
five steps outlined in Scheme 3. In the second case, the identities
of the aldimine and aryl nitromethane were reversed (to 2c and
3a, respectively), and (S,S)-BenzMAM (ent-10) was deployed to
promote a similarly highly diastereo- and enantioselective
addition. The adduct 4ac was converted to the corresponding
cis-imidazoline, but the amine produced by nitro reduction was
subjected to ureaas opposed to amideformation. Depro-
tection, amide formation, and dehydrative cyclization then
furnished the identical cis-imidazoline 11. Hence, by using an
enantiomeric catalyst and reversing the order of amide and urea
formation in the finishing sequence, the same enantiomer of
cis-imidazoline was formed by straightforward permutation of
aldimine and aryl nitromethane substrates.
Each case illustrated in Scheme 3 works equally well such that
less obvious factors might lead one to choose one route over the
other. However, we have identified situations where only one of
the two options may be optimal, or even available. For example,
we targeted the cis-imidazoline 15 (Scheme 4) bearing
p-chloroaryl and m-(trifluoromethoxy)aryl substituents. At-
tempts to prepare the aryl nitromethane 3i bearing a
m-trifluoromethoxy substituent were unsuccessful. Although
aldoximine 13 was isolated in 53% yield, a range of oxidants
uniformly failed to yield the nitroalkane, presumably due to the
electron-withdrawing nature of the substituent (Scheme 4).
Conversely, α-amido sulfone formation and its conversion to the
corresponding aldimine 2b was successful. Since p-chloroaryl
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a b
,
Table 3. Comparative Analysis of Aldimine−Aryl Nitromethane Reactant Pairs in the Catalyzed Aza-Henry Reaction
a
b
All reactions employed 1.1 equiv of nitroalkane in toluene (0.1 M) at −20 °C with 24−36 h reaction time. Catalyst prepared from (R,R)-
cyclohexanediamine or (S,S)-cyclohexanediamine (denoted ent). Diastereomeric ratio (dr) and enantiomeric excess (ee) were determined by chiral
HPLC following vacuum filtration or silica column chromatography (see the Supporting Information). All yields presented are isolated yields.
Scheme 3. Adaptable Synthesis Arriving at the Same (4S,5R)-Nutlin Derivative but Originating from Constitutional Isomeric Aza-
Henry Adducts
nitromethane 3a is readily available, this combination could be
transformed into the desired cis-imidazoline 15 (Scheme 4). By
employment of (S,S)-BenzMAM (ent-10), the desired β-amino
nitroalkane enantiomer ent-4ab was generated in −94% ee and
6:1 dr (Scheme 5).34 Nitro group reduction with CoCl2 and
NaBH4 produced the free amine. Subsequent isocyanate
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with TFA afforded the free amine, which underwent an acylation
with acid 18 using EDC coupling conditions to generate benz-
amide urea 19. Triphenylphosphine oxide and triflic acid gener-
ated a phosphonium anhydride in situ (Hendrickson’s reagent),35
promoting regioselective dehydrative cyclization to provide the
imidazoline 15 as a single diastereomer in 94% ee.
Scheme 4. Comparative Analysis: Unsuccessful and
Successful Preparations of 3-Trifluoromethoxy Aryl
Nitromethane and N-Boc Imine, Respectively
This ability to generate nonsymmetrical cis-imidazolines from
a host of halogenated arenes could provide a platform for further
derivatization using common metal-catalyzed transformations.
For example, we postulated that the bromoaryl derivative 11
(Scheme 6) might be functionalized selectively, as oxidative
addition should be accelerated in comparison to the neighboring
chloroarene. Traditional palladium cross couplings under various
conditions to generate new sp2−sp2 C−C bonds or sp2 carbon−
heteroatom bonds should be substrate compatible.36 We decided
to employ traditional Suzuki cross-coupling conditions with
Pd(0)−tetrakis(triphenylphosphine) and an aryl boronic ester
(20) to test this hypothesis (Scheme 6).37 After the mixtue was
stirred for 24 h at 75 °C, formation of the desired pyrazole adduct
21 was confirmed by its isolation in 62% yield. The aryl chloride
subunit was clearly intact (confirmed by HRMS), and oxidation
to imidazole was not observed. This example establishes the
feasibility of late-stage, site-selective functionalization from
differentiated haloarenes leading to novel heterocyclic derivatives
within this family.
a
Conditions: H2NOH·HCl, pyr, EtOH, room temperature, 53%.
b
c
Conditions: MCPBA, DCM. Conditions: pTolSO2H, BocNH2,
d
Et2O, room temperature, 27%. Conditions: Cs2CO3, Na2SO4, THF,
room temperature, 98%.
Medicinal Chemistry and SAR. The synthetic studies
detailed above were driven in part by a parallel program in
the detailed exploration of cis-imidazolines as inhibitors of
protein−protein interactions. We investigated the binding sites
of MDM2 reported from its cocrystal structure complexed with
(−)-Nutlin-3 (PDB 4HG7) to improve the MDM2-p53 (WT)
binding inhibitory activity. These compounds are uniformly
more potent in their binding to MDM2 as the 4S,5R-configured
cis-imidazolines; therefore, their preparation in high ee was
considered paramount. As a part of the effort not only to
explore MDM2 affinity but also to access structural novelty,
our focus was on three hydrophobic side chains that exist
within the p53 binding pocket (Phe19, Trp23, and Leu26) and
structural modifications were made to both cis-arenes (Ar1 and
Ar2, Table 4) employing the optimal synthetic pathway (cf. top
and bottom equations in Figure 1). We also addressed
optimization of para substituents of ring A by replacing the
electron-donating group (methoxy) with electron-withdraw-
ing groups, including halogens and a nitrile, to explore elec-
trostatic effects. A total of 12 cis-imidazoline analogues were
designed and prepared to probe structure−activity relation-
ships (SAR; Table 4).
Scheme 5. Strategy To Access the Desired (4S,5R)-Nutlin
Derivative, Calling for the (1S,2R)-Aza-Henry Adduct To Be
Employed
According to recent literature,38,39 affinity for MDM2 can be
improved by varying the aromatic substituents on the phenyl ring
that occupy the Leu26 pocket and by enhancing a π−π stacking
formation using carbonyl diimidazole and its reaction with oxo-
piperazine 16 led to urea 17. Straightforward Boc deprotection
Scheme 6. Nonsymmetrical Halogenated Nutlin Analogues Allowing for Regioselective Cross-Coupling Reaction
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Table 4. MDM2 Inhibition Activity of cis-Imidazoline Derivatives
interaction with the His96 residue on MDM2. In an attempt
to occupy the Leu26 pocket, several analogues were designed
and synthesized by introducing different halogens and other
functional groups at either the para or meta position on the Ar2
ring. From the outset, it was clear that any substituents larger
than Cl at the meta position slightly decreased the affinity (15,
23, and 27). However, the only slightly larger p-Br-substituted
compound 11 showed potency equivalent with that of 1. An
exception to this trend was the N-methylpyrazole 21, which was
surprisingly well tolerated given its size. In order to explore
possible secondary interactions with a loop of MDM2 crossing
the binding site, substituents (halogen, nitrile) were introduced
on the para position of the A ring to replace the methoxy group
(R group in Table 4); no dramatic improvement was observed,
but these analogues still exhibited submicromolar affinities (24,
25, 28, and 30).
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measured and are not corrected. Optical rotations were measured using
a polarimeter. Absolute and relative configuration of the aza-Henry
adducts (4aa−4hk) were assigned by analogy to previously synthesized
adducts, for which a crystal structure was obtained.19
Scheme 7 gives the general scheme to access cis-imidazoline/Nutlin
derivatives.
CONCLUSION
■
Generalization of the first highly selective aza-Henry addition
reaction between aryl nitromethanes and aryl Boc-imines has
been achieved, leading to orthogonally protected, cis-stilbene
diamine precursors (up to 99% ee as a single diastereomer). The
unprecedented selectivity reported for this transformation lies in
the discovery of novel mono(amidine) (MAM) bifunctional
catalysts that not only afford aza-Henry adducts in high levels of
stereocontrol but can achieve this at noncryogenic temperature
(−20 °C). The goal to generalize these additions to include an
array of aryl nitromethanes and aryl Boc-imine substrates was
achieved. In cases where a nitroalkane/imine pair led to an
addition product with low stereoselection, a strategy-level
solution was postulated and reduced to practice, involving a
straightforward exchange of nitroalkane/imine identity. By
utilization of this methodology, a number of biologically active
cis-imidazoline small molecules reminiscent of the Nutlin family
were accessed from enantioenriched aza-Henry adducts in
subsequent transformations. The realization that constitutionally
isomeric products could be transformed to the same cis-
imidazoline small molecule (see Scheme 3) further improved
access, and this was demonstrated in cases where exchange
of electrophile and pronucleophile identity in the aza-Henry step
led to a combination with markedly higher stereoselection.
Operationally, synthetic points of variation for this strategy when
pursuing a target synthesis are (1) the sense of the chiral catalyst
employed (R,R vs S,S diamine) and (2) the sequence of amine
coupling reactionsboth of which are easily manipulated.
More broadly, the ability to access enantioenriched, protected cis-
stilbene diamines now allows for direct and predictable
functionalization at each nitrogenan unsolved problem associated
with approaches based on meso-stilbene diamine intermediates.
Furthermore, unsymmetrical Nutlin-3 analogues bearing differ-
entiated haloarenes can be selectively functionalized via late-stage
cross-coupling reactions, allowing for more direct access to
analogues for screening aimed at PPI drug discovery efforts.
Scheme 7. General Scheme To Access cis-Imidazoline/Nutlin
a
Derivatives
Protein Expression and Purification. GST-MDM2 (1-188) was
cloned, expressed, and purified as described previously.18
Fluorescence Polarization (FP) Assay. The fluorescence polar-
ization (FP) assay was performed with 1 μM GST-MDM2 (1-188) in
10 mM Tris (pH 8.0), 42.5 mM NaCl, and 0.0125% Tween-20 assay
buffer. For testing, a dilution series of small molecules (spanning 10 mM
to 0.5 μM in DMSO, in 3-fold steps) was added by direct addition to
protein using pin transfer (100ss pins, V&P Scientific), giving a test
dilution series spanning 65 μM to 3.2 nM with a final concentration of
0.65% DMSO. The increasing concentrations of small molecules
dissolved in DMSO were preincubated with protein for 30 min in black
384-well plates and then treated with Texas Red labeled wild-type p53
peptide (15 nM, amino acids 15−29: GSGSSQETFSDLWKLLPEN)
and incubated for an additional 45 min. After incubation the FP signal
was measured on a multilabel plate reader fitted with a 555 nm excitation
filter, 632 nm static and polarized filters, and a Texas Red FP dichroic
mirror. Unlabeled WT-p53 peptide was used as a positive control, and
DMSO was used as a negative control.
Technical triplicate data were normalized to the positive (100%
inhibition) and negative (0% inhibition) controls on the corresponding
row of the 384-well plate (percentage inhibition = 100 × ((sample
result) − (negative control))/((positive control mean) − (negative
control))). Two to seven independent experiments of normalized data
were combined into a data set and then fit using a nonlinear regression in
GraphPad Prism with the formula log (inhibitor) vs response − variable
slope (four parameters). Additionally the residuals of the curve fit were
plotted to determine the fit of the theoretical curve. IC50 and 95%
confidence intervals (CI) were determined from these graphs.
Among the designed Nutlin analogues, four new compounds
(SJ000773209-5, SJ000773211-3, SJ000801055-1, and
SJ000801057-1) showed levels of MDM2-p53 inhibition activity
similar to that of (−)-Nutlin-3 (1), measured by a fluorescence-
polarization assay. These findings provide a robust framework
together with a streamlined, enantioselective synthesis in which
to develop an in vivo candidate for MDM2-p53 inhibition, as well
as pursue cis-imidazoline-class MDMX-p53 inhibitors.
EXPERIMENTAL SECTION
■
All reagents and solvents were commercial grade and were purified prior
to use when necessary. Toluene (tol) and dichloromethane (CH2Cl2)
were dried by passage through a column of activated alumina as
described by Grubbs.40 Aldimines not included were prepared as
reported in the literature.41 Thin-layer chromatography (TLC) was
performed using glass-backed silica gel (250 μm) plates, and flash
chromatography utilized 230−400 mesh silica gel. UV light and/or the
use of potassium iodoplatinate and potassium permanganate solutions
were used to visualize products. IRA-900-NO2 resin was prepared by
washing IRA900-Cl resin with aqueous NaNO2 until the wash no longer
tested positive for chloride by an AgNO3 test.
Nuclear magnetic resonance spectra (NMR) were acquired at 400,
500, or 600 MHz, and chemical shifts were measured relative to residual
solvent peaks as an internal standard set to δ 7.26 and 77.0 (CDCl3). IR
spectra were recorded as neat films on a NaCl plate (transmission) and
are reported in wavenumbers (cm−1). Mass spectra were recorded on a
high-resolution spectrometer by use of the ionization method noted
(APCI or ESI) and used TOF mass analysis. Melting points were
(E)-tert-Butyl 3-(Trifluoromethoxy)benzylidenecarbamate
(2b). In a flame-dried flask equipped with a magnetic stir bar were
placed Na2SO4 (384 mg, 2.69 mmol), Cs2CO3 (293 mg, 8.98 μmol),
and tert-butyl (tosyl(3-(trifluoromethoxy)phenyl)methyl)carbamate
(200 mg, 449 μmol). The solids were suspended in THF (2.2 mL) at
room temperature. The mixture was monitored by 1H NMR and
vigorously stirred for 75 min. The solution was filtered through a plug of
Celite with excess dichloromethane and concentrated to a white oil
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which was 90% pure by 1H NMR (128 mg, about 98%). This material
was used without further purification: H NMR (400 MHz, CDCl3)
temperature. After 48 h, the mixture was quenched with saturated
aqueous NaHCO3 and the aqueous layer was extracted with
dichloromethane. The combined organic layers were dried (MgSO4),
filtered, and concentrated. Column chromatography (SiO2, 0−2%
methanol in dichloromethane) of the residue provided the compound as
a bronze oil (502 mg, 46%): Rf = 0.85 (CH2Cl2); IR (film) 3074, 2915,
2369, 1761, 1560, 1491 cm−1; 1H NMR (400 MHz, CDCl3) δ 7.56 (m,
2H), 7.06 (t, J = 8.8 Hz, 1H), 5.47 (s, 2H); 13C NMR (100 MHz,
1
δ 8.82 (s, 1H), 7.80 (d, J = 6.8 Hz, 2H), 7.51 (t, J = 8.0 Hz, 1H), 7.40 (m,
1H), 1.58 (s, 9H). The extent to which this compound was prone to
decomposition precluded acquisition of the remaining analytical data.
(E)-tert-Butyl 4-Iodobenzylidenecarbamate (2e). In a flame-
dried round-bottom flask equipped with a magnetic stir bar were placed
MgSO4 (888 mg, 7.4 mmol), Cs2CO3 (240 mg, 0.74 mmol), and
then tert-butyl ((4-iodophenyl)(tosyl)methyl)carbamate (175 mg,
0.37 mmol). The solids were suspended in THF (2.8 mL), and the
mixture was stirred for 4.5 h at room temperature and then filtered
through a bed of Celite on an oven-dried frit and washed with
dichloromethane. Concentration of the filtrate revealed a white oil
(106 mg, 87%) that solidified after sitting in a freezer at −20 °C
overnight to give a white waxy solid: mp 46 °C; Rf = 0.40 (20% EtOAc/
hexanes); IR (film) 2978, 2931, 1715, 1629, 1584, 1483 cm−1; 1H NMR
(400 MHz, CDCl3) δ 8.81 (s, 1H), 7.85 (d, J = 8.0 Hz, 2H), 7.64 (d,
J = 8.4 Hz, 2H), 1.60 (s, 9H); 13C NMR (100 MHz, CDCl3) ppm 168.6,
162.3, 138.2, 133.4, 131.2, 101.2, 82.5, 27.8; HRMS (ESI) exact mass
calcd for C12H14INNaO2 [M + Na]+ 353.9961, found 353.9955.
(E)-tert-Butyl 3-Iodobenzylidenecarbamate (2f). In a flame-
dried flask equipped with a magnetic stir bar were placed Cs2CO3
(488 mg, 1.50 mmol), Na2SO4 (850 mg, 5.99 mmol), and then tert-butyl
((3-iodophenyl)(tosyl)methyl)carbamate (355 mg, 749 μmol) and
toluene (7.7 mL). The mixture was vigorously stirred for 2.5 h and
3
CDCl3) ppm 161.6 (d, 1JCF = 251 Hz), 135.2, 134.8 (d, JCF = 3 Hz),
119.0 (d, 2JCF = 16 Hz), 117.7 (d, 2JCF = 23 Hz), 116.9 (d, 3JCF = 4 Hz),
72.2 (d, 3JCF = 3 Hz); HRMS (APCI) exact mass calcd for C7H5BrFNO2
[M]+ 232.9482, found 232.9476.
1,2-Dimethoxy-4-(nitromethyl)benzene (3h). 3,4-Dimethoxy-
benzaldehyde (3.0 g, 18.0 mmol), hydroxylamine hydrochloride (1.50 g,
21.7 mmol), pyridine (2.62 mL, 32.5 mmol), and ethanol (6.0 mL) were
combined in a flask at room temperature. The mixture was stirred for
15 h, and ethanol was evaporated under reduced pressure. The mixture
was diluted with EtOAc and washed twice with 1 M aqueous HCl and
once with saturated aqueous NaHCO3 and brine. The organic layer
was dried (MgSO4), filtered, and concentrated to a white crystalline
solid. This material was carried on without further purification. The
resulting aldoxime (3.3 g, 18.2 mmol), MCPBA (6.29 g, 36.4 mmol),
and dichloromethane (18 mL) were combined in a flask at room
temperature. After 18 h, the mixture was quenched with saturated
aqueous NaHCO3 and the aqueous layer was extracted with
dichloromethane. The combined organic layers were dried (MgSO4),
filtered, and concentrated. Column chromatography (SiO2, dichloro-
methane) of the residue provided the compound as a yellow solid
(1.26 g, 36%): mp 66−67 °C; Rf = 0.9 (CH2Cl2); IR (film) 3016, 2948,
2838, 1554, 1506, 1376 cm−1; 1H NMR (400 MHz, CDCl3) δ 7.01 (dd,
J = 2.0, 1.6 Hz, 1H), 6.94 (d, J = 2.0 Hz, 1H), 6.87 (d, J = 8.4 Hz, 1H),
5.36 (s, 2H), 3.89 (s, 6H); 13C NMR (100 MHz, CDCl3) ppm 150.3,
149.2, 123.0, 122.1, 112.6, 111.1, 79.9, 55.9 (2C); HRMS (CI) exact
mass calcd for C9H11NO4 [M]+ 197.0604, found 197.0602.
1
monitored by H NMR. The reaction mixture was filtered through a
plug of Celite with excess dichloromethane and concentrated to a clear
oil containing analytically pure aldimine: IR (film) 2978, 2930, 1719,
1631, 1367, 1255 cm−1; 1H NMR (400 MHz, CDCl3) δ 8.75 (s, 1H),
8.31 (s, 1H), 7.87 (d, J = 7.6 Hz, 1H), 7.82 (d, J = 7.6 Hz, 1H), 7.21 (t, J =
7.6 Hz, 1H), 1.59 (s, 9H); 13C NMR (100 MHz, CDCl3) ppm 167.8,
162.1, 142.1, 138.2, 136.0, 130.5, 129.7, 94.5, 82.7, 27.9 (3C); HRMS
(ESI) exact mass calcd for C12H14INNaO2 [M + Na]+ 353.9967, found
353.9961.
(E)-tert-Butyl 5-Bromo-2-fluorobenzylidenecarbamate (2j). In
a flame-dried flask equipped with a magnetic stir bar were placed sodium
sulfate (7.95 g, 56 mmol), potassium carbonate (6.77 g, 49 mmol), and
tert-butyl ((5-bromo-2-fluorophenyl)(tosyl)methyl)carbamate (3.11 g,
7.0 mmol). The solids were suspended in THF (70 mL), and the
mixture was refluxed for 7 h, cooled, filtered through an oven-dried
frit, and concentrated in vacuo to reveal a white oil (1.881 g, 89%) which
solidified to a white waxy solid after being stored at −20 °C: mp
39−40 °C; Rf = 0.47 (30% EtOAc/hexanes); IR (film) 2982, 2930, 1728,
1621, 1584 cm−1; 1H NMR (400 MHz, CDCl3) δ 9.06 (s, 1H), 8.27 (d,
J = 6.0 Hz, 1H), 7.63 (m, 1H), 7.05 (dd, J = 9.2, 9.2 Hz, 1H), 1.59 (s,
9H); 13C NMR (100 MHz, CDCl3) ppm 162.7 (d, 1JCF = 256 Hz), 161.1
(d, 4JCF = 5 Hz), 137.7 (d, 4JCF = 8 Hz), 130.8 (d, 3JCF = 15 Hz), 123.6 (d,
3JCF = 10 Hz), 117.8 (d, 2JCF = 22 Hz), 117.5 (d, 4JCF = 3 Hz), 82.9, 27.8;
1-Methoxy-3-(nitromethyl)benzene (3i). In a 200 mL flask were
placed silver nitrite (1.68 g, 10.94 mmol) and 1-methoxy-3-benzyl
bromide (2.0 g, 9.95 mmol). The flask was purged with N2 and covered
with aluminum foil. At room temperature, THF (80 mL) was added via
syringe. The reaction mixture was stirred at room temperature in the
dark for 46 h and then filtered and concentrated. The crude product was
purified on a column (SiO2, 0−20% ethyl acetate in hexanes) to give the
desired product as a pale yellow solid (0.60 g, 36%): Rf = 0.9 (CH2Cl2);
1
IR (film) 3069, 2916, 2365, 1760, 1558, 1310 cm−1; H NMR (400
MHz, CDCl3) δ 7.38−7.31 (m, 1H), 7.03 (dt, J = 7.6, 1.3 Hz, 1H), 7.01−
6.95 (m, 2H), 5.41 (s, 2H), 3.83 (s, 3H); 13C NMR (101 MHz, CDCl3)
δ 160.0, 130.9, 130.1, 122.1, 115.6, 115.3, 80.0, 55.4; HRMS (ESI) exact
mass calcd for C8H10NO3 [M + H]+ 168.0661, found 168.0662.
General Procedure for Amidine−Amide Catalyst Preparation
(9, 10). The synthesis was derived from the previously reported
assembly of chiral bis(amidine) catalysts.43
HRMS (ESI) exact mass calcd for C12H14BrFNO2 [M + H]+ 302.0192,
found 302.0193.
2-((1R,2R)-2-((4-Chloroquinolin-2-yl)amino)cyclohexyl)-
isoindoline-1,3-dione (S1). A flame-dried flask equipped with a stir
bar was charged with Pd(dba)2 (208 mg, 362 μmol), rac-BINAP
(225 mg, μmol), cesium carbonate (8.84 g, 27.1 mmol), the amine
(2.21 g, 9.05 mmol), and 2,4-dichloroquinoline (1.79 g, 9.05 mmol). An
oven-dried condenser was attached, and the apparatus was purged twice
with argon. Toluene (45 mL) was added, and the resulting solution was
stirred under reflux for 27 h. The reaction mixture was then cooled to
room temperature, filtered through a Celite pad with CH2Cl2 and EtOAc, and
concentrated. Flash column chromatography of the residue afforded the de-
sired product as a light yellow foam (1.53 g, 42%): [α]D20 = +96° (c 0.68,
CHCl3); Rf = 0.31 (20% EtOAc/hexanes); IR (film) 3381, 3060, 2935,
2858, 1767, 1705, 1606, 1567, 1531 cm−1; 1H NMR (400 MHz, CDCl3)
δ 7.65 (d, J = 7.6 Hz, 1H), 7.49 (m, 3H), 7.38 (ddd, J = 8.0, 6.8, 1.2 Hz,
1H), 7.31 (dd, J = 5.6, 3.2 Hz, 2H), 7.06 (ddd, J = 8.0, 8.0, 1.2 Hz, 1H),
6.59 (s, 1H), 4.84 (dddd, J = 10.8, 10.8, 10.8, 4.0 Hz, 1H), 4.74 (d, J =
10.0 Hz, 1H), 4.08 (ddd, J = 10.8, 10.8, 4.0 Hz, 1H), 2.66 (dddd, J = 12.8,
12.8, 12.8, 3.6 Hz, 1H), 2.23 (br m, 1H), 1.85 (m, 3H), 1.66 (ddddd, J =
13.2, 13.2, 13.2, 3.2, 3.2 Hz, 1H), 1.42−1.30 (m, 2H); 13C NMR (125.8
MHz, CDCl3) ppm 168.8, 156.0, 148.1, 142.3, 133.1, 131.3, 129.9,
General Procedure for the Preparation of Nitroalkanes 3a−h
via Aldoxime.42 Aldehyde (1.00 mmol), pyridine (1.80 mmol),
hydroxylamine hydrochloride (1.20 mmol), and ethanol (333 μL) were
combined (in order) in a flask at room temperature. The mixture was
stirred for 1−20 h, and ethanol was evaporated under reduced pressure.
The mixture was diluted with EtOAc, washed twice with 1 M aqueous
HCl, once with saturated aqueous NaHCO3, and brine. The organic
layer was dried (MgSO4), filtered, and concentrated to a white
crystalline solid. Flash column chromatography was used if needed.
The aldoxime (1.00 mmol), MCPBA (2.0−3.0 mmol), and
dichloromethane (1.0 mL) were combined in a flask at room
1
temperature. The reaction was monitored by TLC or H NMR, and
after 1−3 days the mixture was quenched with saturated aqueous
NaHCO3 and the aqueous layer was extracted with dichloromethane.
The combined organic layers were dried (MgSO4), filtered, and con-
centrated. Column chromatography (SiO2, MeOH/dichloromethane)
of the residue provided the title compound.
5-Bromo-2-fluoro-4-(nitromethyl)benzene (3d). (E)-5-Bromo-
2-fluorobenzaldehyde oxime (1.01 g, 4.63 mmol), MCPBA (1.60 g,
9.27 mmol), and dichloromethane were combined in a flask at room
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126.3, 123.3, 122.4, 122.3, 120.9, 111.0, 56.1, 51.3, 33.4, 28.7, 25.5, 24.8;
HRMS (ESI) exact mass calcd for C23H21ClN3O2 [M + H]+ 406.1322,
found 406.1308.
with N-((1R,2R)-2-((4-chloroquinolin-2-yl)amino)cyclohexyl)-
pivalamide (40.0 mg, 111 μmol), pyrrolidine (37.0 μL, 445 μmol),
and trifluorotoluene (800 μL). This suspension was heated at 150 °C
and stirred in the microwave for 90 min. The reaction mixture was
concentrated and purified by flash column chromatography (1−10%
methanol in dichloromethane w/1% AcOH) to provide a yellow oil.
This material was diluted with dichloromethane and washed with 6 M
aqueous NaOH. The organic layers were combined and washed three
times more with 3 M aqueous NaOH. The combined organic layers
were dried (MgSO4) and concentrated to afford a tan amorphous solid
(23.5 mg, 54%): mp 251−256 °C; [α]D20 = +143° (c 0.69, CHCl3); Rf =
0.35 (5% MeOH/1% AcOH/CH2Cl2); IR (film) 3299, 2929, 2856,
2361, 1630, 1588, 1534 cm−1; 1H NMR (600 MHz, CDCl3) δ 7.97 (d,
J = 7.8 Hz, 1H), 7.58 (br d, J = 7.8 Hz, 1H), 7.47 (br s, 1H), 7.42 (dd, J =
7.8, 7.8 Hz, 1H), 7.06 (dd, J = 7.8, 7.8 Hz, 1H), 5.64 (s, 1H), 4.34 (br s,
1H), 4.21 (m, 1H), 3.60−3.54 (m, 5H), 2.22 (br d, J = 11.4 Hz, 1H),
2.06 (br m, 1H), 1.99 (m, 4H), 1.80 (br d, J = 10.8 Hz, 1H), 1.73 (br d,
J = 12.0 Hz, 1H), 1.46−1.28 (m, 4H), 0.84 (s, 9H); 13C NMR (150.9
MHz, CDCl3) ppm 178.9, 158.1, 153.9, 149.6, 128.7, 126.6, 124.9,
119.8, 118.8, 92.0, 57.5, 52.3, 52.0, 38.3, 33.5, 32.4, 27.3, 25.8, 25.4, 24.6;
HRMS (ESI) exact mass calcd for C24H34N4NaO [M + Na]+ 417.2630,
found 417.2630.
(1R,2R)-N1-(4-Chloroquinolin-2-yl)cyclohexane-1,2-diamine
(S2). In a flask equipped with a stir bar were placed the quinoline
(596 mg, 1.47 mmol) and ethanol (3 mL), and the resulting solution was
stirred at room temperature for 5 min. Hydrazine monohydrate (264 μL,
5.43 mmol) was added, and the reaction mixture was stirred under reflux
for 3 h, whereupon a white solid precipitated out of solution. After the
reaction mixture was cooled to room temperature, the solid was washed
with ether and filtered. The remaining solid was triturated with ether, the
suspension was filtered once more, and the filtrate was concentrated to
an orange foam (401 mg, 99%): [α]D20 = −3.3° (c 0.61, CHCl3); Rf =
0.25 (10% MeOH/1%AcOH/CH2Cl2); IR (film) 3268, 2930, 2857,
1609, 1538 cm−1; 1H NMR (400 MHz, CDCl3) δ 7.91 (d, J = 8.0 Hz,
1H), 7.61 (d, J = 8.4 Hz, 1H), 7.49 (ddd, J = 8.4, 8.4, 1.2 Hz, 1H), 7.20
(ddd, J = 8.0, 8.0, 0.8 Hz, 1H), 6.75 (s, 1H), 5.19 (d, J = 8.4 Hz, 1H), 3.64
(m, 1H), 2.44 (ddd J = 10.0, 10.0, 4.0 Hz, 1H), 2.07 (br m, 1H), 1.90 (br
m, 1H), 1.69−1.64 (br m, 4H), 1.39−1.14 (m, 3H), 1.07 (ddd, J = 12.8,
12.8, 3.2 Hz, 1H); 13C NMR (125.8 MHz, CDCl3) ppm 156.7, 148.5,
142.4, 130.2, 126.1, 123.7, 122.3, 121.3, 111.0, 57.4, 55.8, 35.2, 32.5,
24.9, 24.8; HRMS (ESI) exact mass calcd for C15H19ClN3 [M + H]+
276.1268, found 276.1260.
N-((1R,2R)-2-((4-(pyrrolidin-1-yl)quinolin-2-yl)amino)-
cyclohexyl)-3,5-bis(trifluoromethyl)benzamide (10). A 2−5 mL
microwave vial was charged with N-((1R,2R)-2-((4-chloroquinolin-
2-yl)amino)cyclohexyl)-3,5-bis(trifluoromethyl)benzamide (291 mg,
564 μmol), pyrrolidine (185 μL, 2.26 mmol), and trifluorotoluene
(3.52 mL). This suspension was heated at 150 °C and stirred in the
microwave for 90 min. The reaction mixture was concentrated and
purified by flash column chromatography (1−10% methanol in
dichloromethane w/1% AcOH) to provide a yellow oil. This material
was diluted with dichloromethane and washed with 6 M aqueous
NaOH. The organic layers were combined and washed twice more with
3 M aqueous NaOH. The combined organic layers were dried over
MgSO4 and concentrated to afford a white amorphous solid (215 mg,
N-((1R,2R)-2-((4-Chloroquinolin-2-yl)amino)cyclohexyl)-3,5-
bis(trifluoromethyl)benzamide (S3). In a flame-dried flask equipped
with a stir bar were placed the amine (200 mg, 725 μmol), the carboxylic
acid (187 mg, 725 μmol), and dichloromethane (4 mL). The resulting
solution was chilled to 0 °C, and EDC (181 mg, 943 μmol) and DMAP
(9.00 mg, 72.5 μmol) were added. The reaction mixture was stirred and
gradually warmed to room temperature. After 20 h, the reaction mixture
was diluted with water and extracted with CH2Cl2. The combined
organic layers were washed once with water, dried over MgSO4, and
concentrated. Flash column chromatography of the residue (SiO2,
5−40% ethyl acetate in hexanes) afforded the desired amide as a white
amorphous solid (291 mg, 78%): [α]D20 = +291° (c 1.11, CHCl3); Rf =
0.43 (30% EtOAc/hexanes); IR (film) 3335, 2937, 2861, 1654, 1608,
1536 cm−1, 1H NMR (600 MHz, CDCl3) δ 8.60 (br d, J = 5.4 Hz, 1H),
7.94 (s, 2H), 7.93 (dd, J = 9.0, 0.6 Hz, 1H), 7.74 (s, 1H), 7.61 (d, 7.8 Hz,
1H), 7.55 (ddd, J = 7.8, 7.8, 0.6 Hz, 1H), 7.29 (ddd, J = 7.8, 7.8, 0.6 Hz,
1H), 6.71 (s, 1H), 4.70 (d, J = 7.2 Hz, 1H), 4.26 (m, 1H), 3.86 (m, 1H),
2.46 (m, 1H), 2.12 (m, 1H), 1.90 (br dd, J = 5.4, 1.8 Hz, 1H), 1.83 (br s,
1H), 1.47 (m, 4H); 13C NMR (150.9 MHz, CDCl3) ppm 164.9, 156.8,
147.6, 143.3, 137.0, 131.7 (q, JFC = 34.0 Hz, 1C), 131.2, 127.1, 125.7,
124.5 (q, JFC = 3.5 Hz, 1C), 124.1, 123.4, 122.7 (q, JFC = 273.0 Hz, 1C),
121.7, 112.1, 58.9, 53.4, 33.2, 32.1, 25.3, 24.3; HRMS (ESI) exact mass
calcd for C24H21ClF6N3O [M + H]+ 516.1278, found 516.1254.
N-((1R,2R)-2-((4-Chloroquinolin-2-yl)amino)cyclohexyl)-
pivalamide (S4). In a flame-dried flask equipped with a stir bar were
placed the amine (60.0 mg, 218 μmol) and dichloromethane (3 mL),
immediately followed by the addition of N,N-diisopropylethylamine
(46.0 μL, 261 μmol), the acid chloride (32.0 μL, 261 μmol), and DMAP
(2.70 mg, 22.0 μmol). The reaction mixture was stirred at room tem-
perature for 24 h, quenched with 1 M HCl, and extracted with
dichloromethane. The organic extracts were then washed with saturated
aqueous NaHCO3, extracted with dichloromethane, dried (MgSO4),
filtered and concentrated. Flash column chromatography of the residue
(SiO2, 20−50% ethyl acetate in hexanes) afforded the desired amide as a
20
69%): [α]D = +184° (c 0.93, CHCl3); Rf = 0.15 (5% MeOH/1%
AcOH/CH2Cl2); IR (film) 3343, 2935, 2861, 1655, 1589, 1531 cm−1;
1H NMR (600 MHz, CDCl3) δ 9.52 (d, J = 4.2 Hz, 1H), 7.98 (s, 2H),
7.96 (dd, J = 8.4, 0.6 Hz, 1H), 7.73 (s, 1H), 7.51 (d, J = 8.4 Hz, 1H), 7.39
(ddd, J = 8.4, 8.4, 1.2 Hz, 1H), 7.07 (ddd, J = 8.4, 7.2, 1.2 Hz, 1H), 5.65
(s, 1H), 4.34 (br s, 1H), 4.21 (m, 1H), 3.73 (m, 1H), 3.55 (m, 4H), 2.51
(d, J = 12.0 Hz, 1H), 2.07 (m, 1H), 1.98 (m, 4H), 1.87 (d, J = 4.8 Hz,
1H), 1.81 (d, J = 6.0 Hz, 1H), 1.44 (m, 4H); 13C NMR (150.9 MHz,
CDCl3) ppm 165.2, 158.3, 154.0, 149.0, 137.6, 131.5 (q, JFC = 33.7 Hz,
1C), 129.3, 127.3, 126.1, 124.9, 124.2, 122.8 (q, J = 273.1 Hz, 1C), 120.3,
118.6, 91.2, 59.6, 53.1, 51.9, 33.3, 31.9, 25.8, 25.5, 24.4; HRMS (ESI)
exact mass calcd for C28H29F6N4O [M + H]+ 551.2246, found 551.2237.
(E)-5-Bromo-2-fluorobenzaldehyde Oxime (S5). Aldehyde
(2.0 mL, 16.8 mmol), hydroxylamine hydrochloride (1.40 g, 20.2 mmol),
pyridine (2.45 mL, 30.3 mmol), and ethanol (5.6 mL) were combined in
a flask at room temperature. The mixture was stirred for 10 h, and
ethanol was evaporated under reduced pressure. The mixture was
diluted with EtOAc and washed twice with 1 M aqueous HCl and once
with saturated aqueous NaHCO3 and brine. The organic layer was dried
(MgSO4), filtered, and concentrated to give a white crystalline solid
(3.6 g, 98%): mp 76−77 °C; Rf = 0.6 (CH2Cl2); IR (film) 3285 (br),
3079, 3017, 1904, 1492 cm−1; 1H NMR (400 MHz, CDCl3) δ 8.69 (br s,
1H), 8.30 (s, 1H), 7.89 (dd, J = 8.8, 4.0 Hz, 1H). 7.46 (m, 1H), 6.97 (t,
J = 9.2 Hz, 1H); 13C NMR (100 MHz, CDCl3) ppm 161.0 (d, 1JCF = 255
Hz), 143.1 (d, 3JCF = 3 Hz), 134.2, 129.6 (d, 3JCF = 3 Hz), 121.8, 117.7
(d, 2JCF = 22 Hz), 117.1 (d, 3JCF = 3 Hz); HRMS (APCI): exact mass
calcd for C7H5BrFNO [M]+ 216.9533, found 216.9539.
20
white solid (57.9 mg, 74%): mp 213-216 °C; [α]D = +281° (c 0.45,
CHCl3); Rf = 0.38 (40% EtOAc/hexanes); IR (film) 3313, 2932, 2858,
1607, 1576, 1535 cm−1; 1H NMR (600 MHz, CDCl3) δ 7.96 (dd, J = 7.8,
0.6 Hz, 1H), 7.64 (d, J = 7.8 Hz, 1H), 7.56 (ddd, J = 8.4, 6.6, 1.2 Hz, 1H),
7.27 (ddd, J = 7.8, 7.8, 1.2 Hz, 1H), 6.84 (d, J = 6.0 Hz, 1H), 6.71 (s, 1H),
5.03 (br d, J = 7.8 Hz, 1H), 4.18 (m, 1H), 3.71 (m, 1H), 2.16 (m, 2H),
1.82 (m, 1H), 1.78 (d, J = 10.8 Hz, 1H), 1.47−1.28 (m, 4H), 0.87 (s,
9H); 13C NMR (150.9 MHz, CDCl3) ppm 179.1, 156.7, 148.3, 142.6,
130.5, 126.2, 124.0, 122.6, 121.6, 112.2, 56.1, 53.5, 38.4, 33.1, 32.5, 27.3,
25.1, 24.7; HRMS (ESI) exact mass calcd for C20H26ClN3NaO [M +
Na]+ 382.1662, found 382.1658.
General Procedure for Enantioselective Aza-Henry Additions
(4aa−hk). Aryl Boc-imine (4a−k; 100 μmol) and BenzMAM (10;
2.8 mg, 5.0 μmol) or PivMAM (9; 2.0 mg, 5.0 μmol) were dispensed
into a flame-dried vial with a stir bar. Toluene (1.0 mL) was added, and
the reaction was stirred at room temperature until homogeneous. The
reaction mixture was chilled to −78 °C before the aryl nitroalkane 3a−i
(110 μmol) was added. The reaction mixture was warmed to −20 °C
and stirred for 18−60 h. The chilled mixture was either diluted with
N-((1R,2R)-2-((4-(Pyrrolidin-1-yl)quinolin-2-yl)amino)-
cyclohexyl)pivalamide (9). A 0.5−2 mL microwave vial was charged
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CH2Cl2 to dissolve precipitate and quickly flushed through a pad of silica
gel or diluted with cold hexanes and filtered through a Buchner funnel
with filter paper (scale ≥0.2 mmol). Vacuum filtration with cold hexanes
resulted in analytically pure material. If the product was added to silica,
the pad was flushed with CH2Cl2, the filtrate was concentrated, and the
residue was purified by column chromatography (SiO2, ethyl acetate in
hexanes), if needed.
tert-Butyl ((1R,2S)-2-(4-Chlorophenyl)-2-nitro-1-(3-
(trifluoromethoxy)phenyl)ethyl)carbamate (4ab). Imine 2b
(163 mg, 564 μmol) and (S,S)-10 (15.4 mg, 28 μmol) were placed in
a flask in toluene (5.6 mL) under argon. The mixture was cooled to
−20 °C, and nitroalkane 3a (106 mg, 620 μmol) was added. After 48 h
the reaction mixture was filtered through a plug of silica gel and
concentrated. Column chromatography (SiO2, 0−15% ethyl acetate in
hexanes) afforded the product as a white crystalline solid (160 mg, 62%).
The major diastereomer was determined to be 94% ee and the minor to
be 92% ee, with 6:1 dr determined by chiral HPLC (Chiralcel AD: 6%
iPrOH/hexanes, 1.0 mL/min: tr(d2e2 minor/minor) = 11.5 min, tr(d1e1
major/major) = 13.4 min, tr(d1e2 major/minor) = 15.4 min, tr(d2e1
minor/major) = 20.3 min): mp 145 °C; Rf = 0.58 (20% EtOAc/
hexanes); IR (film) 3372, 2981, 2927, 1686, 1558, 1498 cm−1; 1H NMR
(400 MHz, CDCl3) δ 7.49 (d, J = 8.4 Hz, 1H), 7.39 (m, 4H), 7.29 (m,
2H), 7.20 (m, 1H), 5.78 (br dd, 1H), 5.61 (br d, 2H), 1.28 (s, 9H); 13C
NMR (100 MHz, CDCl3) ppm 154.7, 154.3, 139.5, 136.6, 130.5, 130.0,
129.6, 129.3, 129.2 (2C), 125.7, 125.4, 124.7, 121.2, 120.4 (q, 1JCF = 249
Hz), 119.9, 93.0, 28.3, 28.0; HRMS (APCI): exact mass calcd for
C20H20ClF3N2NaO5 [M + Na]+ 483.0911, found 483.0907.
tert-Butyl ((1R,2S)-2-(4-Bromophenyl)-1-(4-chlorophenyl)-2-
nitroethyl)carbamate (4ba). Imine 2a (348 mg, 1.45 mmol) and
(R,R)-10 (40.0 mg, 73.0 μmol) were placed in a flask in toluene
(14.5 mL) under argon. The mixture was cooled to −78 °C and
nitroalkane 3b (377 mg, 1.61 mmol) added. After 36 h the white
precipitate was vacuum-filtered and washed with hexanes to afford the
title compound as a white crystalline solid (493 mg, 75%). The major
diastereomer was determined to be 94% ee with >200:1 dr determined
by chiral HPLC (Chiralcel IA: 15% iPrOH/hexanes, 1.0 mL/min: tr(d1e2
be 90% ee, with 3:1 dr determined by chiral HPLC (Chiralcel IA: 10%
iPrOH/hexanes, 0.8 mL/min: tr(d1e1 minor/major) = 17.6 min, tr(d1e2
minor/minor) = 18.6 min, tr(d2e1 major/major) = 20.9 min, tr(d1e2
major/minor) = 44.6 min): mp 184−185 °C; Rf = 0.30 (25% EtOAc/
hexanes); IR (film) 3505, 3374 (br), 2976, 2935, 1698, 1561, 1492 cm−1;
1H NMR (400 MHz, CDCl3) δ 7.85 (dd, J = 2.4, 2.4 Hz, 1H), 7.52 (m,
1H), 7.36 (d, J = 7.6 Hz, 2H), 7.30 (d, J = 7.6 Hz, 2H), 7.04 (t, J = 8.8 Hz,
1H), 6.10 (d, J = 10.4 Hz, 1H), 5.64 (br d, 1H), 4.84 (d, J = 9.6 Hz, 1H),
1.29 (s, 9H); 13C NMR (100 MHz, CDCl3) ppm 161.0 (d, 1JCF = 259
Hz), 154.6, 135.3, 135.0, 134.9, 130.9, 129.4, 129.2, 128.5, 128.2 (d,
3JCF = 4 Hz), 127.9 (d, 3JCF = 4 Hz), 120.8 (d, 2JCF = 24 Hz), 117.3, 85.4,
28.0; HRMS (APCI) exact mass calcd for C19H19BrClFN2NaO4
[M + Na]+ 495.0098, found 495.0107.
tert-Butyl ((1S,2R)-1-(4-Chlorophenyl)-2-(3-fluorophenyl)-2-
nitroethyl)carbamate (4ea). This compound was prepared according
to the general procedure employing catalyst (R,R)-10 (5 mol %) with a
48 h reaction time. The reaction precipitate was added to the filter paper
of a Buchner funnel and washed with cold hexanes to afford the adduct
as a white crystalline solid (42 mg, 54%), which was found to be 35:1 dr
and 92% ee by chiral HPLC analysis (Chiralpak AD-H, 8% iPrOH/
hexanes, 1 mL/min, tr(d1e1, major/major) = 21.6 min, tr(d2e2, minor/
minor) = 23.8 min, tr(d2e2, minor/minor) = 30.9 min, tr(d1e2, major/
minor) = 40.2 min): mp 162−164 °C; Rf = 0.53 (33% EtOAc/hexanes);
1
IR (film) 3379, 2977, 1680, 1553, 1523, 1289, 1252, 1160 cm−1; H
NMR (400 MHz, CDCl3) δ 7.35 (m, 6 H), 7.18 (m, 2 H), 5.80 (s, 1 H),
5.59 (s, 1 H), 4.92 (s, 1 H), 1.31 (s, 9H); 13C NMR (100 MHz, CDCl3)
ppm 163.8, 161.3, 154.2, 135.6, 134.8, 133.4, 133.3, 131.2, 130.5, 130.4,
129.2, 129.1, 129.0, 128.6, 128.3, 128.2, 125.2, 124.5, 117.5, 117.3, 115.9,
115.6, 93.2, 93.1, 80.8, 28.2, 28.1, 28.0, 27.8; HRMS exact mass calcd for
C19H20ClFN2NaO4 [M + Na]+ 417.0993, found 417.1101.
tert-Butyl ((1R,2S)-1-(4-Chlorophenyl)-2-nitro-2-(m-tolyl)-
ethyl)carbamate (4fa). This compound was prepared according
to the general procedure employing catalyst (R,R)-9 (5 mol %) with a
60 h reaction time. Column chromatography (SiO2, 0−5% ethyl acetate
in hexanes) afforded the adduct as a white crystalline solid (22 mg, 65%),
which was found to be 21:1 dr and 93% ee by chiral HPLC analysis
i
major/minor) = 10.2 min, tr(d2e1 minor/major) = 11.8 min, tr(d1e1
(Chiralpak AD-H, 10% PrOH/hexanes, 1.0 mL/min: tr(d2e1, minor/
20
major/major) = 24.2 min, tr(d2e2 minor/minor) = 33.4 min): [α]D
=
major) =17.9 min, tr(d1e2,, major/minor) = 22.0 min, tr(d2e2, minor/
minor) = 26.3, tr(d1e1, major/major) = 32.0 min). The 79% ee and 34:1
dr material was used for optical rotation: [α]D20 −25.8° (c 1.13, CHCl3);
mp 127−130 °C; Rf = 0.56 (33% EtOAc/hexanes); IR (film) 3385,
−23° (c 0.27, CHCl3); mp 183−184 °C; Rf = 0.40 (20% EtOAc/
hexanes); IR (film) 3375, 2980, 1683, 1544, 1523 cm−1; 1H NMR (400
MHz, CDCl3) δ 7.55 (d, J = 8.4 Hz, 2H), 7.43 (d, J = 8.4 Hz, 2H), 7.34
(d, J = 8.4 Hz, 2H), 7.27 (d, J = 8.4 Hz, 2H), 5.74 (d, J = 8.8 Hz, 1H),
5.57 (dd, J = 9.2, 8.8 Hz, 1H), 4.82 (br d, 1H), 1.28 (s, 9H); 13C NMR
(100 MHz, CDCl3) ppm 154.2, 134.8, 132.1, 130.3, 129.3, 129.0, 128.6,
128.2, 124.8, 93.2, 30.9, 28.0; HRMS (ESI) exact mass calcd for
C19H20BrClN2NaO4 [M + Na]+ 477.0193, found 477.0211.
1
1681, 1548, 1521, 1365, 1161 cm−1; H NMR (400 MHz, CDCl3) δ
7.37−7.22 (m, 8 H), 5.72 (d, J = 8.8 Hz, 1 H), 5.61 (dd, J = 8.8, 8.8 Hz, 1
H), 4.74 (d, J = 7.6 Hz, 1 H), 2.39 (s, 3 H), 1.28 (s, 9 H); 13C NMR (100
MHz, CDCl3) ppm 138.8, 134.5, 131.4, 131.1, 130.8, 129.1, 128.8,
128.6, 125.6, 94.0, 68.1, 38.7, 28.9, 28.2, 28.0, 23.7, 22.9, 21.3; HRMS
(ESI) exact mass calcd for C20H23ClN2NaO4 [M + Na]+ 413.1244,
found 413.1252.
tert-Butyl ((1R,2S)-2-(3-Chlorophenyl)-1-(4-chlorophenyl)-2-
nitroethyl)carbamate (4ca). This compound was prepared according
to the general procedure employing catalyst (R,R)-9 (5 mol %) with a 48
h reaction time. The reaction precipitate was added to the filter paper a
Buchner funnel and washed with cold hexanes to afford the product
as a white crystalline solid (35 mg, 81%) that was found to be 93% ee
tert-Butyl ((1R,2S)-2-(3-Bromophenyl)-1-(4-chlorophenyl)-2-
nitroethyl)carbamate (4ga). This compound was prepared accord-
ing to the general procedure employing catalyst (R,R)-9 (5 mol %) with
a 48 h reaction time. The crude product that precipitated out was filtered
and washed with cold hexanes to give a off-white crystalline solid (740
mg, 78%) that was found to be 92% ee and 25:1 dr by chiral HPLC
(Chiralcel AD-H: 8% EtOH/hexanes, 1.0 mL/min: tr(d1e2 major/
minor) = 11.5 min, tr(d2e1 minor/major) = 14.0 min, tr(d1e1 minor/
minor) = 18.6 min, tr(d2e2 major/major) = 21.3 min): [α]D20 = −26.7°
(c 0.26, CH3OH); mp 172−173 °C; IR (film) 3388, 2982, 1681, 1549,
1519, 1493 cm−1; 1H NMR (400 MHz, CDCl3) δ 7.71 (t, J = 1.8 Hz,
1H), 7.62−7.55 (m, 1H), 7.52 (d, J = 7.9 Hz, 1H), 7.38−7.33 (m, 2H),
7.33−7.27 (m, 3H), 5.75 (s, 1H), 5.56 (t, J = 9.7 Hz, 1H), 4.83 (s, 1H),
1.28 (s, 9H); 13C NMR (126 MHz, CD3OD) δ 156.8, 138.2, 135.9,
135.5, 134.4, 133.0, 131.7, 130.3, 130.0, 128.6, 123.5, 94.5, 80.9, 57.1,
28.4; HRMS (ESI) exact mass calcd for C19H20BrClN2NaO4 [M + Na]+
477.0193, found 477.0218.
i
and >200:1 dr by chiral HPLC (Chiralcel IA: 9% PrOH/hexanes,
0.6 mL/min: tr(d1e1 major/major) = 12.6 min, tr(d2e1 minor/major) =
15.0 min, tr(d1e2 major/minor) = 17.1 min, tr(d2e2 minor/minor) =
18.6 min): [α]D20 = −37° (c 0.44, CHCl3); mp 182−183 °C; Rf = 0.55
(25% EtOAc/hexanes); IR (film) 3389, 3056, 2980, 1683, 1490 cm−1;
1H NMR (400 MHz, CDCl3) δ 7.57 (m, 1H), 7.44 (m, 2H), 7.37−7.28
(m, 5H), 5.76 (br d, 1H), 5.56 (br dd, 1H), 4.86 (br d, 1H), 1.29 (s, 9H);
13C NMR (100 MHz. CDCl3) ppm 154.2, 134.9, 134.8, 133.1, 130.5,
130.3, 130.2, 130.1, 129.3, 129.1, 128.9, 128.6, 128.3, 128.0, 126.8, 93.2,
28.1; HRMS (ESI) exact mass calcd for C19H20Cl2N2NaO4 [M + Na]+
433.0698; found 433.0715.
tert-Butyl ((1R,2S)-2-(5-Bromo-2-fluorophenyl)-1-(4-chloro-
phenyl)-2-nitroethyl)carbamate (4da). The reaction was run with
catalyst (R,R)-8 (2 mol %) at −78 °C for 8 h and the mixture was then
warmed to −20 °C for an additional 24 h. Following silica plug removal
of the catalyst, column chromatography (SiO2, 0−10% ethyl acetate in
hexanes) afforded the product as a white crystalline solid (422 mg, 65%).
The major diastereomer was determined to be 92% ee and the minor to
tert-Butyl ((1R,2S)-1-(4-Chlorophenyl)-2-(3,4-dimethoxy-
phenyl)-2-nitroethyl)carbamate (4ha). This compound was
prepared according to the general procedure employing catalyst
(R,R)-10 (5 mol %) with a 48 h reaction time. Column chromatography
(SiO2, 10−25% ethyl acetate in hexanes) afforded the adduct as an
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off-white solid (56.0 mg, 76%) that was found to be 76% ee and 37:1 dr
by chiral HPLC (Chiralcel IA: 12% iPrOH/hexanes, 1.0 mL/min: tr(d2e1
(400 MHz, CDCl3) δ 7.71 (d, J = 8.4 Hz, 2H), 7.49 (d, J = 8.4 Hz, 2H),
7.40 (d, J = 8.4 Hz, 2H), 7.09 (d, J = 8.4 Hz, 2H), 5.75 (d, J = 8.8 Hz,
1H), 5.55 (dd, J = 9.4, 8.8 Hz, 1H), 4.76 (d, J = 9.2 Hz, 1H), 1.27 (s, 9H);
13C NMR (100.6 MHz, (CD3)2SO) ppm 154.7, 138.4, 137.9, 135.4,
minor/major) = 16.9 min, tr(d1e1 major/major) = 19.2 min, tr(d1e2
20
major/minor) = 20.1 min, tr(d2e2 minor/minor) = 25.5 min): [α]D
=
−4.5° (c 0.40, CHCl3); mp 148−149 °C; Rf = 0.25 (CH2Cl2); IR (film)
3367, 2975, 2837, 1703, 1557, 1521 cm−1; 1H NMR (400 MHz, CDCl3)
δ 7.33 (d, J = 8.8 Hz, 2H), 7.29, (d, J = 8.8 Hz, 2H), 7.07 (d, J = 4.0 Hz,
1H), 7.05 (d, J = 2.0 Hz, 1H), 6.86 (d, J = 8.4 Hz, 1H), 5.70 (d, J = 10.0
Hz, 1H), 5.64 (d, J = 8.4 Hz, 1H), 4.82 (d, J = 8.4 Hz, 1H), 3.90 (s, 3H),
3.89 (s, 3H), 1.28 (s, 9H); 13C NMR (100 MHz, CDCl3) ppm 154.3,
150.7, 149.2, 136.2, 134.6, 129.2, 128.6, 123.5, 122.1, 110.9, 93.9, 80.6,
56.0 (2C), 28.1; HRMS (ESI) exact mass calcd for C21H25ClN2NaO6
[M + Na]+ 459.1299, found 459.1309.
131.1, 130.9, 130.3, 129.2, 95.3, 92.9, 79.2, 55.9, 28.2; HRMS (ESI)
exact mass calcd for C19H20ClIN2NaO4 [M + Na]+ 525.0054, found
525.0082.
tert-Butyl ((1S,2R)-2-(4-Chlorophenyl)-1-(3-iodophenyl)-2-
nitroethyl)carbamate (ent-4af). This compound was prepared
according to the general procedure employing catalyst (S,S)-9 (5 mol %)
with a 72 h reaction time. The reaction precipitate was added to the filter
paper of a Buchner funnel and washed with cold hexanes to afford the
adduct as a white crystalline solid (360 mg, 80%). The major
diastereomer was determined to be 99% ee with >200:1 dr determined
tert-Butyl ((1R,2S)-1-(4-Chlorophenyl)-2-(3-methoxyphenyl)-
2-nitroethyl)carbamate (4ia). The reaction employed catalyst (R,R)-
9 (5 mol %) with a 48 h reaction time. The crude precipitated product
was filtered and washed with cold hexanes to give a white solid (1.05 g,
87%) that was found to be 95% ee and 23:1 dr by chiral HPLC (Chiralcel
AD: 10% EtOH/hexanes, 1.0 mL/min: tr(d2e1 minor/major) = 9.1 min,
tr(d1e1 major/major) = 11.3 min, tr(d2e2 minor/minor) = 13.0 min,
i
by chiral HPLC (Chiralcel AD-H: 15% PrOH/hexanes, 0.6 mL/min:
tr(d1e1 major/major) = 14.3 min, tr(d2e2 minor/minor) = 15.2 min,
tr(d1e2 major/minor) = 29.5 min, tr(d2e1 minor/minor) = 32.4 min):
20
[α]D = +220° (c 0.20, CHCl3); mp 170−172 °C; Rf = 0.45 (20%
EtOAc/hexanes); IR (film) 3393, 2981, 2360, 1679, 1545, 1518 cm−1;
1H NMR (400 MHz, CDCl3) δ 7.68 (m, 2H), 7.49 (d, J = 7.6 Hz, 2H),
1
tr(d1e2 major/minor) = 32.1 min): H NMR (400 MHz, CDCl3) δ
7.39 (d, J = 7.6 Hz, 2H), 7.30 (d, J = 7.6 Hz, 1H), 7.09 (dd, J = 7.6, 7.6
Hz, 1H), 5.72 (br d, J = 9.2 Hz, 1H), 5.55 (br dd, 1H), 4.82 (br d, 1H),
1.28 (s, 9H); 13C NMR (100 MHz, CDCl3) ppm 154.1, 139.4, 138.0,
136.6, 136.1, 130.7, 130.1, 129.7, 129.4, 129.1, 126.6, 94.8, 93.1, 28.0;
HRMS (ESI) exact mass calcd for C19H20ClIN2NaO4 [M + Na]+
525.0054, found 525.0071.
7.37−7.27 (m, 5H), 7.09 (dd, J = 5.1, 2.8 Hz, 2H), 7.00−6.94 (m, 1H),
5.73 (d, J = 9.8 Hz, 1H), 5.62 (d, J = 9.8 Hz, 1H), 4.89 (s, 1H), 3.82 (s,
3H), 1.27 (s, 9H); LRMS (ESI) C20H24ClN2O5 [M + H]+ 406.86, found
407.58.
tert-Butyl ((1S,2R)-1-(4-Bromophenyl)-2-(4-chlorophenyl)-2-
nitroethyl)carbamate (ent-4ac). This compound was prepared
according to the general procedure employing catalyst (S,S)-10
(5 mol %)with a 36 h reaction time. The reaction precipitate was
added to the filter paper in a Buchner funnel and washed with cold
hexanes to afford the adduct as a white crystalline solid (310 mg, 88%)
that was found to be 93% ee with >200:1 dr determined by chiral HPLC
tert-Butyl ((1R,2S)-2-(4-Chlorophenyl)-2-nitro-1-(m-tolyl)-
ethyl)carbamate (4ag). This compound was prepared according to
the general procedure employing catalyst (R,R)-10 (5 mol %) with a
48 h reaction time, and following silica filtration the product was isolated
as a white crystalline solid (48 mg, 98% overall) that was found to be
88% ee and 50:1 dr by chiral HPLC (Chiralpak IA, 10% iPrOH/hexanes,
1 mL/min, tr(d1e1 major/major) = 9.6 min, tr(d2e2 minor/minor) = 12.4
min, tr(d1e2 minor/major) = 14.9, tr(d1e2 major/minor) = 32.7 min):
[α]D20 = −38° (c 0.11, CHCl3, recrystallized material, 96% ee, 200:1 dr);
mp 186−188 °C; Rf = 0.56 (33% EtOAc/hexanes); IR (film)
i
(Chiralcel AD-H: 15% PrOH/hexanes, 1.0 mL/min: tr(d1e1 major/
major) = 10.5 min, tr(d2e1 minor/minor) = 12.4 min, tr(d1e2 major/
minor) = 22.0 min, tr(d2e1 minor/minor) = 36.7 min): [α]D20 = +28°
(c 0.24, CHCl3); mp 185−186 °C; Rf = 0.42 (20% EtOAc/hexanes); IR
(film) 3389, 2976, 1681, 1552, 1519, 1498 cm−1; 1H NMR (400 MHz,
CDCl3) δ 7.49 (m, 4H), 7.38 (d, J = 8.4 Hz, 2H), 7.21 (d, J = 8.4 Hz,
2H), 5.75 (br d, 1H), 5.56 (br dd, 1H), 4.84 (br d, 1H), 1.28 (s, 9H);
13C NMR (100 MHz, CDCl3) ppm 154.2, 136.6, 132.2, 130.1, 129.7,
129.1, 128.9, 123.0, 93.1, 20.0; HRMS (ESI) exact mass calcd for
C19H20BrClN2NaO4 [M + Na]+ 477.0193, found 477.0216.
1
3399, 2984, 2921, 2359, 1688 cm−1; H NMR (400 MHz, CDCl3) δ
7.55 (d, J = 8.4 Hz, 2 H), 7.41 (d, J = 8.4 Hz, 1 H), 7.28 (m, 2 H), 7.15
(m, 3 H), 5.76 (d, J = 10.0 Hz, 1 H), 5.64 (m, 1 H), 4.71 (d, J = 9.6 Hz, 1
H), 2.48 (s, 3 H), 1.3 (s, 9 H); 13C NMR (100 MHz, CDCl3) ppm 154.2,
138.9, 137.0, 136.3, 130.2, 130.0, 129.7, 129.0, 128.9, 127.9, 124.0,
94.6, 80.4, 56.5, 28.0, 21.4; HRMS (ESI) exact mass calcd for
C20H23ClN2NaO4 [M + Na]+ 413.1243, found 413.1262.
tert-Butyl ((1R,2S)-2-(4-Chlorophenyl)-1-(4-fluorophenyl)-2-
nitroethyl)carbamate (4ad). This compound was prepared accord-
ing to the general procedure employing catalyst (R,R)-10 (5 mol %)
with a 48 h reaction time. Column chromatography (SiO2, 1−10% ethyl
acetate in hexanes) afforded the adduct as an off-white crystalline solid
(21 mg, 82%) that was found to be 94% ee and 9:1 dr by chiral HPLC
tert-Butyl ((1R,2S)-1-(3-Chlorophenyl)-2-(4-chlorophenyl)-2-
nitroethyl)carbamate (4ah). This compound was prepared accord-
ing to the general procedure employing catalyst (R,R)-10 (5 mol %)
with a 24 h reaction time. Column chromatography (SiO2, 0−5% ethyl
acetate in hexanes) afforded the adduct as a white crystalline solid
(23 mg, 71%) that was found to be 97% ee and 9:1 dr determined by
i
(Chiralcel AD-H: 8% PrOH/hexanes, 1.0 mL/min: tr(d1e2 major/
i
minor) = 11.7 min, tr(d2e1 major/minor) = 19.6 min, tr(d1e1 major/
major) = 25.7 min, tr(d2e2 minor/minor) = 40.2 min): mp 179−181 °C;
Rf = 0.49 (20% EtOAc/hexanes); IR (film) 3378, 2977, 2922, 1678,
1560, 1519 cm−1; 1H NMR (400 MHz, CDCl3) δ 7.51 (d, J = 8.4 Hz,
2H), 7.40 (d, J = 8.4 Hz, 2H), 7.32 (dd, J = 8.4, 8.4 Hz, 2H), 7.05 (dd, J =
8.4, 8.4 Hz, 2H), 5.75 (br d, 1H), 5.59 (br dd, 1H), 4.80 (br d, 1H), 1.28
(s, 9H); 13C NMR (150 MHz, CDCl3) ppm 162.4 (d, 1JCF = 249 Hz),
154.2, 136.5, 133.0, 130.1, 129.8, 129.1, 129.0 (d, 4JCF = 7.5 Hz), 116.1
chiral HPLC (Chiralcel IA: 5% PrOH/hexanes, 1.0 mL/min: tr(d2e2
minor/minor) = 18.4 min, tr(d2e1 minor/major) = 21.3 min, tr(d1e1
major/major) = 31.3 min, tr(d1e1 major/minor) = 47.8 min): mp 174−
175 °C; Rf = 0.58 (20% EtOAc/hexanes); IR (film) 3385, 2977, 1685,
1553, 1526 cm−1; 1H NMR (400 MHz, CDCl3) δ 7.50 (d, J = 8.0 Hz,
2H), 7.39 (d, J = 8.0 Hz, 2H), 7.34−7.22 (m, 4H), 5.73 (br d, 1H), 5.60
(br m, 1H), 4.71 (br d, 1H), 1.28 (s, 9H); 13C NMR (100 MHz, CDCl3)
ppm 154.2, 139.2, 136.6, 135.0, 130.4, 130.1, 129.7, 129.1, 127.4, 125.5,
93.1, 28.0; HRMS (ESI) exact mass calcd for C19H20Cl2N2NaO4 [M +
Na]+ 433.0698, found 433.0713.
2
(d, JCF = 23 Hz), 93.4, 80.8, 28.0; HRMS (ESI) exact mass calcd for
C19H20ClFN2NaO4 [M + Na]+ 417.0993, found 417.1010.
tert-Butyl ((1S,2R)-2-(4-Chlorophenyl)-1-(4-iodophenyl)-2-
nitroethyl)carbamate (ent-4ae). This compound was prepared
according to the general procedure employing catalyst (S,S)-10
(5 mol %) with a 24 h reaction time. Column chromatography (SiO2,
0−5% ethyl acetate in hexanes) afforded the adduct as a white crystalline
solid (27 mg, 84%) that was found to be a 99% ee and >100:1 dr by chiral
tert-Butyl ((1R,2S)-2-(4-Chlorophenyl)-1-(3-fluorophenyl)-2-
nitroethyl)carbamate (4ai). This compound was prepared according
to the general procedure employing catalyst (R,R)-10 (5 mol %) with an
18 h reaction time, and following silica gel filtration, the product was
isolated as a white crystalline solid (37 mg, 98%), which was found to be
60:1 dr and 88% ee by chiral HPLC analysis (Chiralpak AD-H, 5%
iPrOH/hexanes, 1.0 mL/min: tr(d2e1, minor/major) =28.7 min, tr(d1e2,
major/minor) = 34.8 min, tr(d1e1, major/major) = 48.5, tr(d2e2, minor/
minor) = 70 min): [α]D20 =−11°(c 0.11, CHCl3, 40% ee); mp 169−171 °C;
Rf = 0.58 (33% EtOAc/hexanes); IR (film) 3383, 2983, 1681, 1551, 1524,
1366, 1162 cm−1; 1H NMR (400 MHz, CDCl3) δ 7.53 (d, J = 8.4 Hz, 2 H),
i
HPLC; (ChiralPak AD-H, 15% PrOH/hexanes, 1.0 mL/min: tr(d1e1,
major/major) = 11.8 min, tr (d2e1, minor/major) = 14.1 min, tr (d1e1,
20
major/major) = 22.8 min, tr (d2e2, minor/minor = 42.4 min): [α]D
+
22° (c 0.16, CHCl3); mp 189−190 °C; Rf = 0.50 (20% EtOAc in
1
hexanes); IR (film) 3380, 2979, 1679, 1548, 1520 cm−1; H NMR
6925
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Article
7.42 (d, J = 8.4 Hz, 2 H), 7.37 (m, 1 H), 7.15 (d, J = 8.0 Hz, 1 H), 7.08
(m, 2 H), 5.77 (br d, 1 H), 5.64 (br dd, 1 H), 4.86 (br d, 1 H), 1.30 (s, 9 H);
13C NMR (100 MHz, CDCl3) ppm 164.1, 161.6, 136.6, 130.74, 130.66,
130.0, 129.6, 129.1, 122.8, 116.0, 115.8, 114.4, 114.2, 93.1, 27.9; HRMS
(ESI) exact mass calcd for C19H20ClFN2NaO4 [M + Na]+ 417.0993,
found 417.1080.
(100 MHz, CDCl3) ppm 159.6 (d, 1JCF = 249 Hz), 154.6, 147.9, 135.3,
134.8 (d, 3JCF = 7.5 Hz), 132.2 (2C), 131.0, 128.4 (2C), 122.7, 120.9 (d,
3JCF = 13.5 Hz), 117.7, 117.6, 85.5 (d, 3JCF = 3 Hz), 28.1; HRMS (ESI)
exact mass calcd for C19H19Br2FN2NaO4 [M + Na]+ 538.9593, found
538.9606.
tert-Butyl ((1R,2S)-1-(4-Bromophenyl)-2-nitro-2-(m-tolyl)-
ethyl)carbamate (4fc). This compound was prepared according to
the general procedure employing catalyst (R,R)-9 (5 mol %) with a 48 h
reaction time. Column chromatography (SiO2, 0−10% ethyl acetate in
hexanes) afforded the adduct as an off-white crystalline solid (29 mg,
92%) that was found to be 87% ee and 7:1 dr by chiral HPLC (Chiralcel
tert-Butyl ((1R,2S)-1-(5-Bromo-2-fluorophenyl)-2-(4-chloro-
phenyl)-2-nitroethyl)carbamate (4aj). This compound was pre-
pared according to the general procedure employing catalyst (R,R)-10
(5 mol %) with a 48 h reaction time. Column chromatography (SiO2,
0−5% ethyl acetate in hexanes) afforded an off-white crystalline solid
(29.0 mg, 53%) that was found to be 84% ee and 25:1 dr by chiral HPLC
i
AD-H: 8% PrOH/hexanes, 1.0 mL/min: tr(d2e1 minor/major) =
i
(Chiralcel AD: 6% PrOH/hexanes, 1.0 mL/min: tr(d1e2 minor/
25.9 min, tr(d2e2 minor/minor) = 30.8 min, tr(d1e2 major/minor) =
38.3 min, tr(d1e1 major/major) = 43.8 min): mp 165−166 °C; Rf = 0.53
(25% EtOAc/hexanes); IR (film) 3379, 2965, 2924, 2848, 1689, 1551,
1517 cm−1; 1H NMR (400 MHz, CDCl3) δ 7.48 (d, J = 8.4 Hz, 2H), 7.40
(m, 1H), 7.35 (s, 1H), 7.31 (m, 2H), 7.23 (d, J = 8.4 Hz, 2H), 5.71 (br d,
1H), 5.58 (br dd, 1H), 5.44 (br d, 1H), 2.37 (s, 3H), 1.27 (s, 9H); 13C
NMR (100 MHz, CDCl3) ppm 154.3, 138.8, 136.8, 131.1, 129.2, 129.0,
128.8, 128.7, 127.5, 125.6, 122.7, 93.9, 29.7, 28.2, 28.0; HRMS (ESI)
exact mass calcd for C20H23BrN2NaO4 [M + Na]+ 457.0689, found
457.0696.
major) = 12.9 min, tr(d2e1 minor/major) = 14.6 min, tr(d2e2 minor/
minor) = 29.6 min, tr(d1e1 major/major) = 32.8 min): [α]D20 = −11° (c
0.40, CHCl3); mp 165 °C (dec.); Rf = 0.60 (20% EtOAc/hexanes); IR
(film) 3327, 2980, 2924, 1704, 1565, 1489 cm−1; 1H NMR (400 MHz,
CDCl3) δ 7.54 (d, J = 8.0 Hz, 2H), 7.44 (m, 1H), 7.41 (d, J = 8.0 Hz,
2H), 7.28 (m, 1H), 7.00 (dd, J = 8.8, 8.8 Hz, 1H), 5.80 (br d, 1H),
5.64 (br d, 1H), 5.07 (br d, 1H), 1.24 (s, 9H); 13C NMR (100 MHz,
CDCl3) ppm 159.0 (d, 1JCF = 246 Hz), 154.1, 136.6, 133.7 (d, 3JCF = 8.0
Hz), 132.5, 130.1, 129.5, 129.3, 129.1, 126.0 (d, 3JCF = 13 Hz), 117.9 (d,
2JCF = 23 Hz), 117.3, 92.1, 28.1, 27.9; HRMS (ESI) exact mass calcd for
tert-Butyl ((1R,2S)-1-(4-Bromophenyl)-2-(3,4-dimethoxy-
phenyl)-2-nitroethyl)carbamate (4hc). This compound was pre-
pared according to the general procedure employing catalyst (R,R)-10
(5 mol %) with a 72 h reaction time. Column chromatography (SiO2,
0−5% ethyl acetate in hexanes) afforded the adduct as a white solid (27
mg, 51%) that was found to be 73% ee and 31:1 dr by chiral HPLC
(ChiralPak IA, 7% EtOH/hexanes, 1.0 mL/min: tr(d1e2 major/minor) =
16.1 min, tr(d1e1 major/major) = 18.4 min, tr(d2e2 minor/minor) =
C19H19BrClFN2NaO4 [M + Na]+ 495.0109, found 495.0098.
tert-Butyl ((1R,2S)-1,2-bis(4-Bromophenyl)-2-nitroethyl)-
carbamate (4bc). This compound was prepared according to the
general procedure employing catalyst (R,R)-10 (5 mol %) with a 48 h
reaction time. Column chromatography (SiO2, 0−10% ethyl acetate in
hexanes) afforded the adduct as a white crystalline solid (19 mg, 75%)
that was found to be 84% ee and 9:1 dr by chiral HPLC (Chiralcel IA:
i
20
6% PrOH/hexanes, 1.0 mL/min: tr(d1e1 major/major) = 15.9 min,
21.0 min, tr(d2e1 minor/major) = 28.8 min): [α]D = −5.4° (c 0.37,
tr(d1e2 major/minor) = 17.4 min, tr(d2e1 minor/major) = 20.1 min,
tr(d2e2 minor/minor) = 50.5 min): mp 178−179 °C dec; Rf = 0.54 (20%
EtOAc/hexanes); IR (film) 3370, 2980, 2918, 1679, 1549, 1529 cm−1;
1H NMR (400 MHz, CDCl3) δ 7.55 (d, J = 8.8 Hz, 2H), 7.49 (d, J = 8.8
CHCl3); mp 183−184 °C; Rf = 0.24 (20% EtOAc in hexanes); IR (film)
3376, 2975, 2926, 1687, 1556, 1521 cm−1; 1H NMR (400 MHz, CDCl3)
δ 7.48 (d, J = 8.4 Hz, 2H), 7.23 (d, J = 8.4 Hz, 2H), 7.09−7.05 (m, 2H),
6.85 (d, J = 8.0 Hz, 1H), 5.70 (d, J = 10.0 Hz, 1H), 5.62 (br dd, 1H), 4.86
(d, J = 8.8 Hz, 1H), 3.90 (s, 3H), 3.89 (s, 3H), 1.28 (s, 9H); 13C NMR
(100 MHz, CDCl3) ppm 143.3, 150.7, 149.2, 136.7, 132.1, 129.0 (2C),
128.2, 125.3, 123.5, 122.8, 122.1, 110.9, 93.8, 56.0, 28.1; HRMS (ESI)
exact mass calcd for C21H25BrN2NaO6 [M + Na]+ 503.0794; found
503.0777.
tert-Butyl ((1R,2S)-2-(4-Bromophenyl)-2-nitro-1-(m-tolyl)-
ethyl)carbamate (4bg). This compound was prepared according to
the general procedure employing catalyst (R,R)-10 (5 mol %) with a
48 h reaction time. Following silica plug filtration, the adduct was isolated
as an off-white solid (35 mg, 88%) that was found to be 85% ee and 68:1
dr by chiral HPLC (Chiralcel IA: 7% iPrOH/hexanes, 1.0 mL/min: tr(d2e1
Hz, 2H), 7.42 (d, J = 8.8 Hz, 2H), 7.21 (d, J = 8.8 Hz, 2H), 5.73 (d,
J = 6.8 Hz, 1H), 5.56 (dd, J = 9.6, 8.8 Hz, 1H), 4.85 (br d, 1H), 1.26 (s,
9H); 13C NMR (100 MHz, CDCl3) ppm 154.2, 136.1, 132.3, 132.1,
130.3, 128.9, 128.6, 124.8, 123.0, 93.2, 28.2, 28.0; HRMS (ESI) exact
mass calcd for C19H20Br2N2NaO4 [M + Na]+ 520.9687, found 520.9703.
tert-Butyl ((1R,2S)-1-(4-Bromophenyl)-2-(3-chlorophenyl)-2-
nitroethyl)carbamate (4cc). This compound was prepared according
to the general procedure employing catalyst (R,R)-10 (5 mol %) with a
48 h reaction time. Column chromatography (SiO2, 0−10% ethyl
acetate in hexanes) afforded the adduct as an off-white crystalline solid
(23 mg, 80%) that was found to be 95% ee and 5:1 dr by chiral HPLC
(Chiralcel IA: 10% iPrOH/hexanes, 0.6 mL/min: tr(d1e1 major/major) =
21.0 min, tr(d1e2 major/minor) = 25.1 min, tr(d2e1 minor/major) =
29.6 min, tr(d2e2 major/major) = 30.8 min): mp 184 °C; Rf = 0.49 (25%
EtOAc/hexanes); IR (film) 3368, 2976, 2914, 1677, 1554, 1519 cm−1;
1H NMR (400 MHz, CDCl3) δ 7.57 (s, 1H), 7.50 (d, J = 8.4 Hz, 2H),
minor/major) = 15.6 min, tr(d1e2 major/minor) = 17.5 min, tr(d1e1
20
major/major) = 21.1 min, tr(d2e2 minor/minor) = 49.1 min): [α]D
=
−33° (c 0.54, CHCl3); mp 184−185 °C; Rf = 0.57 (25% EtOAc/
hexanes); IR (film) 3379, 2972, 2917, 1696, 1551, 1517 cm−1; 1H NMR
(400 MHz, CDCl3) δ 7.54 (d, J = 8.0 Hz, 2H), 7.46 (J = 8.0 Hz, 2H),
7.25 (m, 1H), 7.13 (m, 3H), 5.73 (d, J = 9.6 Hz, 1H), 5.6 (br dd, 1H),
4.82 (br d, 1H), 2.35 (s, 3H), 1.27 (s, 9H); 13C NMR (100 MHz,
CDCl3) ppm 154.2, 138.9, 137.0, 132.3, 131.9, 131.6, 130.5, 129.7,
129.0, 127.9, 124.6, 124.0, 93.6, 28.0, 21.4; HRMS (ESI) exact mass
calcd for C20H23BrN2NaO4 [M + Na]+, 457.0739, found 457.0720.
tert-Butyl ((1R,2S)-2-(3-Chlorophenyl)-2-nitro-1-(m-tolyl)-
ethyl)carbamate (4cg). This compound was prepared according to
the general procedure employing catalyst (R,R)-10 (5 mol %) with a
48 h reaction time. Following silica plug filtration, the adduct was
isolated as an off-white crystalline solid (22 mg, 97%) that was found to
7.42 (m, 2H), 7.35 (m, 1H), 7.23 (d, J = 8.4 Hz, 2H), 5.76 (br d, 1H),
5.56 (br dd, J = 8.0 Hz, 1H), 4.85 (br d, 1H) 1.28 (s, 9H); 13C NMR
(100 MHz, CDCl3) ppm 154.2, 136.1, 134.8, 133.1, 132.2, 130.5, 130.2,
128.9, 128.6, 126.8, 123.0, 93.1, 28.0; HRMS (ESI) exact mass calcd for
C19H20BrClN2NaO4 [M + Na]+ 477.0193, found 477.0208.
tert-Butyl ((1R,2S)-2-(5-Bromo-2-fluorophenyl)-1-(4-bromo-
phenyl)-2-nitroethyl)carbamate (4dc). This compound was pre-
pared according to the general procedure employing catalyst (R,R)-10
(5 mol %) with a 36 h reaction time. Column chromatography (SiO2,
0−30% ethyl acetate in hexanes) afforded the adduct as an off-white
crystalline solid (15.0 mg, 80%) that was found to be 93% ee and 3:1 dr
by chiral HPLC (Chiralcel AD-H: 3% EtOH/hexanes, 0.8 mL/min:
tr(d2e2 minor/minor) = 22.8 min, tr(d2e1 minor/major) = 25.6 min,
tr(d1e1 major/major) = 31.0 min, tr(d1e2 major/minor) = 43.5 min): mp
170−171 °C; Rf = 0.6 (20% EtOAc/hexanes); IR (film) 3335, 2975,
2926, 1708, 1563, 1486 cm−1; 1H NMR (400 MHz, CDCl3) δ 7.72 (dd,
J = 6.0, 2.0 Hz, 1H), 7.48 (m, 1H), 7.44 (d, J = 8.8 Hz, 2H), 7.13 (d, J =
8.4 Hz, 2H), 6.94 (dd, J = 9.2, 8.4 Hz, 1H), 6.22 (d, J = 6.0 Hz, 1H), 5.58
(d, J = 6.0 Hz, 1H), 5.52 (d, J = 7.6 Hz, 1H), 1.35 (s, 9H); 13C NMR
i
be 99% ee and 20:1 dr by chiral HPLC (Chiralcel IA: 8% PrOH/
hexanes, 1.0 mL/min: tr(d2e2 minor/minor) = 10.5 min, tr(d1e1 major/
major) = 14.1 min, tr(d1e2 major/minor) = 15.5 min, tr(d2e1 minor/
major) = 23.7 min): mp 151−152 °C; Rf = 0.45 (25% EtOAc/hexanes);
1
IR (film) 3391, 2977, 2922, 1692, 1553, 1519 cm−1; H NMR (400
MHz, CDCl3) δ 7.69 (m, 1H), 7.50 (d, J = 7.2 Hz, 1H), 7.41 (d, J = 8.0
Hz, 1H), 7.28−7.24 (m, 1H), 7.14 (m, 3H), 5.73 (d, J = 9.2 Hz, 1H),
5.60 (br d, 1H), 4.77 (d, J = 9.2 Hz, 1H), 2.36 (s, 3H), 1.27 (s, 9H); 13C
NMR (125 MHz, CDCl3) ppm 154.1, 139.0, 136.9, 133.4, 130.3, 130.0,
6926
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The Journal of Organic Chemistry
Article
129.7, 129.0, 127.9, 126.9, 124.0, 93.6, 28.0, 21.4; HRMS (ESI) exact
mass calcd for C20H23ClN2NaO4 [M + Na]+, 413.1244, found 413.1247.
tert-Butyl ((1R,2S)-2-(5-bromo-2-fluorophenyl)-2-nitro-1-
(m-tolyl)ethyl)carbamate (4dg). This compound was prepared
according to the general procedure employing catalyst (R,R)-9 (5 mol %)
with a 42 h reaction time. Column chromatography (SiO2, 0−10%
ethyl acetate in hexanes) afforded the adduct as an off-white crystalline
solid (34 mg, 80%) that was found to be 68% ee and 5:1 dr by chiral
HPLC (Chiralcel AD: 7% EtOH/hexanes, 1.0 mL/min: tr(d2e1 minor/
major) = 9.5 min, tr(d1e1 major/major) = 10.5 min, tr(d2e2 minor/
minor) = 12.2 min, tr(d1e2 major/minor) = 34.6 min): mp 150−151 °C;
Rf = 0.60 (25% EtOAc/hexanes); IR (film) 3297, 2974, 2919, 1707,
1563, 1487 cm−1; 1H NMR (400 MHz, CDCl3) δ 7.92 (d, J = 4.0 Hz,
1H), 7.51 (m, 1H), 7.25 (m, 1H), 7.16 (m, 2H), 7.00 (m, 2H), 6.12 (d,
J = 10.4 Hz, 1H), 5.61 (d, J = 10.0 Hz, 1H), 4.88 (br d, 1H), 2.36 (s, 3H),
1.26 (s, 9H); 13C NMR (100 MHz, CDCl3) ppm 159.9 (d, 1JCF = 248
tert-Butyl ((1R,2S)-2-(5-Bromo-2-fluorophenyl)-1-(3-chloro-
phenyl)-2-nitroethyl)carbamate (4dh). This compound was
prepared according to the general procedure employing catalyst
(R,R)-10 (5 mol %) with a 24 h reaction time. Following silica plug
1
filtration, H NMR showed 3:1 dr. Column chromatography (SiO2,
0−10% ethyl acetate in hexanes) afforded the adduct as an off-white
crystalline solid (24 mg, 66%) that was found to be 76% ee and 1:1 dr by
chiral HPLC (Chiralcel OJ-H: 3% EtOH/hexanes, 1.0 mL/min: tr(d1e2
major/minor) = 20.2 min, tr(d1e1 major/major) = 22.8 min, tr(d2e2
minor/minor) = 25.3 min, tr(d2e2 minor/minor) = 27.5 min): mp 158−
159 °C; Rf = 0.55 (20% EtOAc/hexanes); IR (film) 3372, 2986, 2924,
1682, 1558, 1524 cm−1; 1H NMR (400 MHz, CDCl3) δ 7.89 (dd, J = 6.0,
2.4, 1H), 7.54 (m, 1H), 7.34 (m, 2H), 7.25 (m, 2H), 7.04 (dd, J = 9.2, 9.2
Hz, 1H), 6.10 (d, J = 9.6 Hz, 1H), 5.66 (br d, J = 9.4 Hz, 1H), 4.90 (br d,
1H), 1.29 (s, 9H); 13C NMR (100 MHz, CDCl3) ppm 158.9 (d, 1JCF
=
249 Hz), 154.0, 138.3, 134.9 (d, 2JCF = 23 Hz), 134.8 (d, 3JCF = 8 Hz),
130.5, 129.3, 127.4, 124.9, 120.8 (d, 3JCF = 12 Hz), 117.6 (d, 2JCF = 24
Hz), 117.3 (d, 4JCF = 3 Hz), 85.6 (d, 4JCF = 4 Hz), 28.0; HRMS (ESI)
exact mass calcd for C19H19BrClFN2NaO4 [M + Na]+, 495.0098, found
495.0115.
3
Hz), 154.1, 139.0, 136.7, 134.7 (d, JCF = 8 Hz), 129.8, 129.1, 127.8,
127.3, 124.0, 121.2 (d, 3JCF = 13 Hz), 117.4 (d, 2JCF = 23 Hz), 117.1 (d,
4JCF = 3 Hz), 85.9 (d, 3JCF = 13 Hz), 28.1, 21.4; HRMS (ESI) exact mass
calcd for C20H22BrFN2NaO4 [M + Na]+, 475.0645, found 475.0663.
tert-Butyl ((1R,2S)-2-Nitro-1,2-bis(m-tolyl)ethyl)carbamate
(4fg). This compound was prepared according to the general procedure
employing catalyst (R,R)-10 (5 mol %) with a 48 h reaction time. The
filtrate was analytically pure, and the adduct was isolated as a white
crystalline solid (40.0 mg, 95%) that was found to be 86% ee and 50:1 dr
tert-Butyl ((1R,2S)-1-(3-Chlorophenyl)-2-nitro-2-(m-tolyl)-
ethyl)carbamate (4fh). This compound was prepared according to
the general procedure employing catalyst (R,R)-10 (5 mol %) with a
48 h reaction time. Column chromatography (SiO2, 0−5% ethyl acetate
in hexanes) afforded the adduct as a white crystalline solid (25 mg, 74%)
that was found to be 85% ee and 8:1 dr by chiral HPLC (Chiralcel AD:
i
by chiral HPLC (Chiralcel AD-H: 10% PrOH/hexanes, 1.0 mL/min:
i
10% PrOH/hexanes, 1.0 mL/min: tr(d2e1 minor/major) = 9.1 min,
tr(d2e1 minor/major) = 9.8 min, tr(d2e2 minor/minor) = 15.2 min, tr(d1e1
20
tr(d1e2 major/minor) = 12.8 min, tr(d2e2 minor/minor) = 14.8 min,
tr(d1e1 major/major) = 15.9 min): mp 153−154 °C; Rf = 0.50 (20%
EtOAc/hexanes); IR (film) 3390, 2980, 1687, 1548, 1515, 1365 cm−1;
1H NMR (400 MHz, CDCl3) δ 7.34−7.23 (m, 8H), 5.71 (d, J = 9.6 Hz,
1H), 5.62 (dd, J = 9.6, 8.0 Hz, 1H), 4.79 (d, J = 8.8 Hz, 1H), 2.38 (s, 3H),
1.27 (s, 9H); 13C NMR (150 MHz. CDCl3) ppm 154.2, 139.7, 138.8,
134.8, 131.2, 131.1, 130.2, 129.2, 128.9 (2C), 127.4, 125.7, 125.5, 94.0,
28.0, 21.3; HRMS (ESI) exact mass calcd for C20H23ClN2NaO4
[M + Na]+ 413.1241; found 413.1245.
tert-Butyl ((1R,2S)-1-(3-Chlorophenyl)-2-(3,4-dimethoxy-
phenyl)-2-nitroethyl)carbamate (4hh). This compound was
prepared according to the general procedure employing catalyst
(R,R)-10 (5 mol %) with a 72 h reaction time. The reaction precipitate
was added to the filter paper of a Buchner funnel and washed with cold
hexanes to afford the product as a light brown crystalline solid (38 mg,
68%) that was found to be 70% ee and 23:1 dr determined by chiral
HPLC (Chiralcel IA: 7% EtOH/hexanes, 1.0 mL/min: tr(d1e2 major/
minor) = 8.5 min, tr(d1e1 major/major) = 9.3 min, tr(d2e1 minor/
major) = 10.6 min, tr(d2e2 minor/minor) = 12.8 min): mp 161−162 °C;
Rf = 0.4 (20% EtOAc/hexanes); IR (film) 3342, 2975, 2940, 1701, 1563,
1521, 1376 cm−1; 1H NMR (400 MHz, CDCl3) δ 7.35 (m, 1H), 7.30−
7.28 (m, 2H), 7.25−7.22 (m, 1H), 7.09−7.05 (m, 2H), 6.85 (d, J = 8.0
Hz, 1H), 5.70 (m, 2H), 4.88 (br d, 1H), 3.90 (s, 3H), 3.89 (s, 3H), 1.28
(s, 9H); 13C NMR (100 MHz, CDCl3) ppm 154.3, 150.7, 149.2, 139.7,
134.8, 130.2, 128.9, 127.4, 125.5, 123.5, 122.1, 93.8, 56.0, 28.6; HRMS
(ESI) exact mass calcd for C21H25ClN2NaO6 [M + Na]+ 459.1299,
found 459.1301.
major/major) = 16.4 min, tr(d1e2 major/minor) = 18.1 min): [α]D
=
−35° (c 0.29, CHCl3); mp 179−180 °C; Rf = 0.38 (25% EtOAc/
hexanes); IR (film) 3384, 2911, 2857, 1686, 1549, 1529 cm−1; 1H NMR
(400 MHz, CDCl3) δ 7.38−7.36 (m, 2H), 7.29 (dd, J = 7.2, 7.2 Hz, 1H),
7.16−7.23 (m, 2H), 7.15−7.13 (m, 3H), 5.72 (d, J = 9.6 Hz, 1H), 5.64
(br dd, 1H), 4.82 (d, J = 8.0 Hz, 1H), 2.38 (s, 3H), 2.35 (s, 3H), 1.26 (s,
9H); 13C NMR (100 MHz, CDCl3) ppm 154.2, 138.7, 138.6, 137.6,
131.5, 130.9, 129.4, 129.3, 128.9, 128.7, 127.9, 125.8, 124.0, 94.4, 80.2,
28.0, 21.4, 21.3; HRMS (ESI) exact mass calcd for C21H26N2NaO4
[M + Na]+ 393.1790, found 393.1794.
tert-Butyl ((1R,2S)-2-(4-Bromophenyl)-1-(3-chlorophenyl)-2-
nitroethyl)carbamate (4bh). This compound was prepared accord-
ing to the general procedure employing catalyst (R,R)-10 (5 mol %)
with a 20 h reaction time. Following silica plug filtration, the product was
isolated as an an off-white crystalline solid (27 mg, 78%) that was found
to be 90% ee and 70:1 dr by chiral HPLC (Chiralcel AD-H: 10% iPrOH/
hexanes, 1.0 mL/min: tr(d2e1 minor/major) = 13.4 min, tr(d1e2 major/
minor) = 14.9 min, tr(d1e1 major/major) = 20.9 min, tr(d2e2 minor/
minor) = 35.9 min): [α]D20 = −30° (c 0.25, CHCl3); mp 175−176 °C;
Rf = 0.54 (25% EtOAc/hexanes); IR (film) 3391 (s), 2991, 2928, 1692,
1560, 1526 cm−1; 1H NMR (400 MHz, CDCl3) δ 7.54 (d, J = 8.0 Hz,
2H), 7.43 (J = 8.0 Hz, 2H), 7.33 (d, J = 8.4 Hz, 2H), 7.29−7.22 (m, 2H),
5.73 (br d, J = 10.0 Hz, 1H), 5.95 (br d, 1H), 4.85 (br d, 1H), 1.28 (s,
9H); 13C NMR (100 MHz, CDCl3) ppm 154.2, 139.1, 135.0, 132.1,
130.4, 130.3, 130.2, 129.1, 127.4, 125.5, 124.8, 93.2, 28.1; HRMS (ESI)
exact mass calcd for C19H20BrClN2NaO4 [M + Na]+, 477.0193, found
477.0190.
tert-Butyl ((1R,2S)-1,2-Bis(3-chlorophenyl)-2-nitroethyl)-
carbamate (4ch). This compound was prepared according to the
general procedure employing catalyst (R,R)-9 (5 mol %) with a 48 h
reaction time. Column chromatography (SiO2, 5−10% ethyl acetate in
hexanes) afforded the adduct as a white crystalline solid (27.0 mg, 90%)
that was found to be 93% ee and 30:1 dr by chiral HPLC; (Chiralcel IA:
tert-Butyl ((1R,2S)-1-(5-Bromo-2-fluorophenyl)-2-(4-bromo-
phenyl)-2-nitroethyl)carbamate (4bj). This compound was pre-
pared according to the general procedure employing catalyst (R,R)-10
(5 mol %) with a 48 h reaction time. Column chromatography (SiO2,
0−10% ethyl acetate in hexanes) afforded the product as an off-white
crystalline solid (95 mg, 87%) that was found to be 86% ee and 60:1 dr
i
i
8% PrOH/hexanes, 1.0 mL/min: tr(d2e1 minor/major) = 10.6 min,
by chiral HPLC (Chiralcel AD-H: 10% PrOH/hexanes, 1.0 mL/min:
tr(d1e2 major/minor) = 12.9 min, tr(d1e1 major/major) = 14.3 min,
tr(d2e2 minor/minor) = 17.5 min): [α]D20 = −44° (c 0.29, CHCl3); mp
170−171 °C; Rf = 0.63 (20% EtOAc/hexanes); IR (film) 3372, 2986,
2924, 1682, 1558, 1524 cm−1; 1H NMR (400 MHz, CDCl3) δ 7.58 (s,
1H), 7.47−7.43 (m, 2H), 7.38−7.31 (m, 3H), 7.30−7.24 (m, 2H), 5.75
(br d, 1H), 5.59 (br dd, 1H), 4.98 (br d, 1H), 1.30 (s, 9H); 13C NMR
(100 MHz, CDCl3) ppm 154.2, 139.1, 135.0, 134.8, 133.0, 130.5, 130.4,
130.2, 129.2, 128.9, 127.4, 126.8, 125.5, 93.1, 28.2; HRMS (ESI) exact
mass calcd for C19H20Cl2N2NaO4 [M + Na]+ 433.0698, found 433.0715.
tr(d1e2 major/minor) = 9.8 min, tr(d2e1 minor/major) = 11.0 min, tr(d1e1
20
major/major) = 21.9 min, tr(d2e2 minor/minor) = 25.9 min): [α]D
=
−14° (c 0.43, CHCl3); mp 160−161 °C; Rf = 0.53 (20% EtOAc/
hexanes); IR (film) 3397, 2982, 2926, 1708, 1563, 1500, 1376 cm−1; 1H
NMR (400 MHz, CDCl3) δ 7.56 (d, J = 8.4 Hz, 2H), 7.51 (m, 1H),
7.49−7.43 (m, 3H), 7.00 (dd, J = 8.8, 8.8 Hz, 1H), 5.79 (m, 2H), 5.04
(br d, 1H), 1.25 (s, 9H); 13C NMR (100 MHz, CDCl3) ppm 160.1
1
3
(, JCF = 241 Hz), 154.1, 133.7 (d, JCF = 9 Hz), 132.3, 132.1, 130.3,
3
2
130.0, 126.0 (d, JCF = 15 Hz), 124.9, 117.9 (d, JCF = 23 Hz), 117.4,
6927
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The Journal of Organic Chemistry
Article
92.3, 28.0; HRMS (ESI) exact mass calcd for C19H19Br2FN2NaO4 [M +
Na]+, 538.9593, found 538.9596.
1H), 7.00 (dd, J = 8.8, 1.6 Hz, 1H), 6.88 (dd, J = 8.0, 8.0 Hz, 1H), 5.77
(m, 2H), 5.00 (d, J = 8.8 Hz, 1H), 3.94 (s, 3H), 3.87 (s, 3H), 1.26 (s,
1
tert-Butyl ((1S,2R)-1-(4-Bromophenyl)-2-(4-chlorophenyl)-2-
nitroethyl)carbamate (4cj). This compound was prepared according
to the general procedure employing catalyst (R,R)-9 (5 mol %) with a
48 h reaction time. Column chromatography (SiO2, 0−5% ethyl acetate
in hexanes) afforded the adduct as a white solid (28 mg, 90%) that was
found to be 88% ee and 8:1 dr determined by chiral HPLC (Chiralcel
9H); 13C NMR (100 MHz, CDCl3) ppm 154.2, 150.1 (d, JCF = 253
Hz), 133.5 (d, 3JCF = 9 Hz), 126.5 (d, 3JCF = 9 Hz), 123.2 (d, 2JCF = 27
2
Hz), 122.3, 122.1, 117.9 (d, JCF = 23 Hz), 117.3, 112.6, 111.1, 110.8,
110.7, 92.8 (d, 4JCF = 5 Hz), 80.5, 56.0 (2C), 28.1; HRMS (ESI) exact
mass calcd for C21H24BrFN2NaO6 [M + Na]+ 521.0699, found
521.0701.
i
AD-H: 8% PrOH/hexanes, 1.0 mL/min: tr(d1e2 major/minor) =
tert-Butyl ((1R,2S)-2-(4-Bromophenyl)-1-(3,4-dimethoxy-
phenyl)-2-nitroethyl)carbamate (4bk). This compound was
prepared according to the general procedure employing catalyst
(R,R)-10 (5 mol %) with a 44 h reaction time. The reaction precipitate
was added to the filter paper of a Buchner funnel and washed with cold
hexanes to afford the product as an off-white crystalline solid (33 mg,
60%) that was found to be 85% ee and 9:1 dr by chiral HPLC (Chiralcel
AD-H: 9% EtOH/hexanes, 1.0 mL/min: tr(d1e2 major/minor) =
16.3 min, tr(d2e1 minor/major) = 19.5 min, tr(d1e1 major/major) =
22.4 min, tr(d2e2 major/major) = 53.5 min): mp 153−154 °C; Rf = 0.19
(25% EtOAc/hexanes); IR (film) 3368, 2973, 2938, 1697, 1551,
1516 cm−1; 1H NMR (400 MHz, CDCl3) δ 7.54 (d, J = 8.8 Hz, 2H), 7.44
(d, J = 8.4 Hz, 2H), 6.86 (m, 3H), 5.76 (d, J = 9.2 Hz, 1H), 5.54 (dd, J =
9.6, 9.2 Hz, 1H), 4.83 (br d, 1H), 3.87 (s, 3H), 1.28 (s, 9H); 13C NMR
(100 MHz, CDCl3) ppm 154.3, 149.4, 149.2, 131.9, 130.6, 130.5, 129.5,
124.6, 119.2, 111.3, 110.6, 93.5, 56.0, 55.9, 28.0; HRMS (ESI) exact
mass calcd for C21H25BrN2NaO6 [M + Na]+, 503.0790, found 503.0794.
tert-Butyl ((1R,2S)-2-(3-Chlorophenyl)-1-(3,4-dimethoxy-
phenyl)-2-nitroethyl)carbamate (4ck). This compound was pre-
pared according to the general procedure employing catalyst (R,R)-10
(5 mol %) with a 60 h reaction time. Following the silica plug filtration,
the resulting white solid was added to the filter paper of a Buchner funnel
and washed with cold hexanes to afford the pure compound as an off-
white solid (15.3 mg, 64%) that was found to be 93% ee and 56:1 dr by
chiral HPLC (Chiralcel AD-H: 6% EtOH/hexanes, 1.0 mL/min: tr(d1e2
10.6 min, tr(d2e1 minor/major) = 13.8 min, tr(d2e2 minor/minor) = 19.1 min,
tr(d1e1 major/major) = 22.2 min): mp 185−186 °C; Rf = 0.45 (20%
EtOAc/hexanes); IR (film) 3361, 2973, 2924, 1710, 1565, 1482 cm−1;
1H NMR (400 MHz, CDCl3) δ 7.60 (s, 1H), 7.54−7.51 (m, 2H), 7.48−
7.42 (m, 2H), 7.40−7.33 (m, 1H), 7.01 (dd, J = 8.8, 8.8 Hz, 1H), 5.80
(m, 2H), 5.03 (d, J = 9.6 Hz, 1H), 1.25 (s, 9H); 13C NMR (150 MHz,
CDCl3) ppm 160.2 (d, 1JCF = 244 Hz), 133.8, 133.7, 132.8, 130.9 (2C),
130.6, 130.2, 129.1, 128.8 (2C), 126.7, 125.9, 118.0 (d, 2JCF = 23 Hz),
117.4, 92.2, 28.1; HRMS (ESI) exact mass calcd for C19H19BrClFN2NaO4
[M + Na]+ 495.0095, found 495.0100.
tert-Butyl ((1R,2S)-1,2-Bis(5-bromo-2-fluorophenyl)-2-
nitroethyl)carbamate (4dj). This compound was prepared according
to the general procedure employing catalyst (R,R)-10 (5 mol %) with
a 48 h reaction time. Column chromatography (SiO2, 0−5% ethyl
acetate in hexanes) afforded the product as a white crystalline solid
(22 mg, 56%) that was found to be 78% ee and 2:1 dr by chiral HPLC;
i
(ChiralPak IA, 10% PrOH/hexanes, 1.0 mL/min: tr(d1e1 major/
major) = 5.9 min, tr(d2e1 minor/major) = 6.5 min, tr(d2e2 minor/
minor) = 7.1 min, tr(d1e2 major/minor) = 8.9 min): mp 156−157 °C;
Rf = 0.78 (20% EtOAc in hexanes); IR (film) 3324, 2965, 2924, 1710,
1565, 1489 cm−1; 1H NMR for both diastereomers reported (600 MHz,
CDCl3) δ 7.91 (s, 1H), 7.72 (dd, J = 4.8 Hz, 1H), 7.53−7.37 (m, 4H),
7.03 (m, 2H), 6.94 (m, 2H), 6.28 (br d, 1H), 6.21 (d, J = 10.8 Hz, 1H),
5.79−5.71 (m, 2H), 5.10 (d, J = 9.6 Hz, 1H), 1.39 (s, 9H), 1.26 (s, 9H);
13C NMR (150 MHz, CDCl3) ppm 159.8 (d, 1JCF = 249 Hz), 159.4 (d,
1JCF = 249 Hz), 154.5, 154.1, 135.0 (2C), 133.9 (2C), 133.7, 133.5,
major/minor) = 19.9 min, tr(d2e1 minor/major) = 23.3 min, tr(d1e1
20
major/major) = 25.5 min, tr(d2e2 minor/minor) = 35.2 min): [α]D
=
−8.8° (c 0.25, CHCl3); mp 185 °C (dec.); Rf = 0.17 (25% EtOAc/
hexanes); IR (film) 3351, 2979, 2937, 1703, 1565, 1517 cm−1; 1H NMR
(400 MHz, CDCl3) δ 7.56 (s, 1H), 7.49 (d, J = 7.2 Hz, 1H), 7.41 (d, J =
8.0 Hz, 1H), 7.35 (m, 1H), 6.89 (d, J = 8.0 Hz, 1H), 6.84 (d, J = 7.6 Hz,
2H), 5.77 (d, J = 9.2 Hz, 1H), 5.54 (dd, J = 9.6, 9.2 Hz, 1H), 4.80 (d, J =
9.2 Hz, 1H), 3.88 (s, 3H), 3.87 (s, 3H), 1.28 (s, 9H); 13C NMR (100
MHz, CDCl3) ppm 154.2, 149.4, 149.3, 134.6, 133.4, 130.3, 130.0,
129.5, 129.1, 126.9, 119.2, 111.4, 110.6, 93.5, 56.0, 55.9, 28.0; HRMS
(ESI) exact mass calcd for C21H25ClN2NaO6 [M + Na]+ 459.1299,
found 459.1322.
tert-Butyl ((1R,2S)-2-(5-Bromo-2-fluorophenyl)-1-(3,4-dime-
thoxyphenyl)-2-nitroethyl)carbamate (4dk). This compound was
prepared according to the general procedure employing catalyst (R,R)-9
(5 mol %) with a 46 h reaction time. The reaction precipitate was added
to the filter paper of a Buchner funnel and washed with cold hexanes to
afford the adduct as a white crystalline solid (22 mg, 45%) that was
found to be 86% ee and 1.5:1 dr by chiral HPLC (Chiralcel IC: 8%
iPrOH/hexanes, 1.0 mL/min: tr(d2e1 minor/major) = 15.1 min, tr(d1e1
major/major) = 16.8 min, tr(d2e2 minor/minor) = 20.0 min, tr(d1e2
major/minor) = 38.3 min): mp 135−136 °C; Rf = 0.27 (25% EtOAc/
hexanes); IR (film) 3391, 2991, 2928, 1692, 1560, 1526 cm−1; 1H NMR
(400 MHz, CDCl3) δ 7.92 (dd, J = 6.0, 2.0 Hz, 1H), 7.51 (m, 1H), 7.02
(d, J = 8.8 Hz, 1H), 6.90 (dd, J = 8.4, 1.6 Hz, 1H), 6.85 (m, 2H), 6.12 (d,
J = 10.0 Hz, 1H), 5.60 (br d, 1H), 4.82 (d, J = 9.6 Hz, 1H), 3.90 (s, 3H),
3.88 (s, 3H), 1.29 (s, 9H); 13C NMR (100 MHz, CDCl3) ppm 159.9 (d,
1JCF = 240 Hz), 149.5, 149.4, 134.7 (d, 3JCF =11 Hz), 132.4 (d, 3JCF = 9
133.4, 132.1, 131.9, 130.1, 125.6, 120.7, 118.2, 118.0, 117.8, 117.6, 117.4
(2C), 117.2, 84.7, 84.4, 81.2, 81.0, 29.7, 28.3, 28.1; HRMS (ESI) exact
mass calcd for C19H18Br2F2N2NaO4 [M + Na]+ 556.9499; found
556.9482.
tert-Butyl ((1R,2S)-1-(5-Bromo-2-fluorophenyl)-2-nitro-2-(m-
tolyl)ethyl)carbamate (4fj). This compound was prepared according
to the general procedure employing catalyst (R,R)-9 (5 mol %) with a 48
h reaction time. Column chromatography (SiO2, 5−10% ethyl acetate in
hexanes) afforded the adduct as a white crystalline solid (23 mg, 42%)
that was found to be 82% ee and 40:1 dr by chiral HPLC (Chiralcel IA:
i
10% PrOH/hexanes, 1.0 mL/min: tr(d2e1 minor/major) = 7.4 min,
tr(d1e1 major/major) = 14.9 min, tr(d1e2 major/minor) = 6.6 min, tr(d2e2
minor/minor) = 9.2 min): [α]D20 = −13° (c 0.31, CHCl3, 76% ee, 20:1 dr);
mp 159−165 °C; Rf = 0.48 (20% EtOAc in hexanes); IR (film) 3450,
3000, 2950, 2410, 1710, 1590, 1490, 1260 cm−1; 1H NMR (400 MHz,
CDCl3) δ 7.53 (br s, 1H), 7.44 (ddd, J = 8.8, 4.8, 2.8 Hz, 1H), 7.38 (s,
1H), 7.36 (s, 1H), 7.31 (t, J = 7.6 Hz, 1H), 7.25 (s, 1H), 7.00 (dd, J =
10.8, 9.2 Hz, 1H), 5.80 (m, 2H), 4.98 (br d, 1H), 2.38 (s, 3H), 1.25 (s,
1
9H); 13C NMR (100 MHz, CDCl3) ppm 159.4 (d, JCF = 249 Hz),
154.5, 138.7, 133.4, 131.1 (d, 3JCF = 8 Hz), 130.9, 129.1, 128.8, 125.6,
118.0, 117.5 (d, 2JCF = 23 Hz), 92.8, 27.9, 21.3; HRMS (ESI) exact mass
calcd for C20H2281BrFN2NaO4 [M + Na]+ 477.0646, found 477.0660.
tert-Butyl ((1R,2S)-1-(5-Bromo-2-fluorophenyl)-2-(3,4-dime-
thoxyphenyl)-2-nitroethyl)carbamate (4hj). This compound was
prepared according to the general procedure employing catalyst (R,R)-
10 (5 mol %) with a 72 h reaction time. Following silica plug filtration,
1H NMR showed >20:1 dr. Column chromatography (SiO2, 10−40%
Hz), 129.2, 126.9, 121.2, 121.1, 119.0, 117.2 (d, 4JCF = 3 Hz), 111.5, 85.5
(d, 4JCF = 2 Hz), 56.0, 55.9, 28.2, 28.0; HRMS (ESI) exact mass calcd for
C21H24BrFN2NaO6 [M + Na]+, 521.0699, found 521.0684.
tert-Butyl ((1R,2S)-1-(3,4-Dimethoxyphenyl)-2-nitro-2-(m-
tolyl)ethyl)carbamate (4fk). This compound was prepared according
to the general procedure employing catalyst (R,R)-9 (5 mol %) with a
36 h reaction time. Column chromatography (SiO2, 0−20% ethyl
acetate in hexanes) afforded the adduct as an off-white crystalline solid
(18 mg, 65%) that was found to be 72% ee and 60:1 dr by chiral HPLC
ethyl acetate in hexanes) afforded the adduct as an off-white solid (31.0
mg, 70%) that was found to be 56% ee and 4:1 dr (racemized on silica)
by chiral HPLC (Chiralcel IA: 12% iPrOH/hexanes, 1.0 mL/min: tr(d1e2
major/minor) = 9.5 min, tr(d2e1 minor/major) = 10.3 min, tr(d2e2
minor/minor) = 16.8 min, tr(d1e1 major/major) = 23.4 min): mp 131−
132 °C; Rf = 0.66 (50% EtOAc/hexanes); IR (film) 3368, 2974, 2928,
1703, 1556, 1518, 1279 cm−1; 1H NMR (400 MHz, CDCl3) δ 7.52 (d,
J = 4.8 Hz, 1H), 7.44 (m, 1H), 7.15 (br s, 1H), 7.09 (dd, J = 8.4, 2.0 Hz,
6928
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Article
i
(Chiralcel IA: 12% PrOH/hexanes, 1.0 mL/min: tr(d2e1 minor/
methanol (4.1 mL) in a flask and chilled to 0 °C before NaBH4 (194 mg,
5.15 mmol) was added in three portions over 2 h. The reaction mixture
was stirred at 0 °C for an additional 15 min before the mixture was
quenched with saturated aqueous NH4Cl. The reaction mixture was
adjusted to pH 10 with concentrated aqueous NH4OH, and the aqueous
layer was extracted with ethyl acetate. The combined organic layers were
dried (MgSO4), filtered, and concentrated to a white foam (416 mg,
95%): [α]D20 = +44° (c 0.80, CHCl3); Rf = 0.40 (50% EtOAc/hexanes);
major) = 13.4 min, tr(d1e2 major/minor) = 18.3 min, tr(d1e1 major/
major) = 22.2 min, tr(d2e2 minor/minor) = 28.8 min): [α]D20 = −16° (c
0.25, CHCl3); mp 146−148 °C; Rf = 0.31 (25% EtOAc/hexanes); IR
(film) 3377, 2987, 2925, 1686, 1549, 1522 cm−1; 1H NMR (400 MHz,
CDCl3) δ 7.36 (m, 2H), 7.31−7.22 (m, 2H), 6.90 (d, J = 8.0 Hz, 1H),
6.83 (m, 2H), 5.74 (d, J = 9.2 Hz, 1H), 5.58 (dd, J = 9.2, 8.8 Hz, 1H),
4.78 (d, J = 8.8 Hz, 1H), 3.87 (s, 6H), 2.37 (s, 3H), 1.27 (s, 9H); 13C
NMR (100 MHz, CDCl3) ppm 154.3, 149.2, 149.1, 138.6, 131.5, 130.9,
130.2, 129.3, 128.7, 125.8, 119.2, 111.3, 110.6, 94.3, 55.9 (2C), 29.7,
28.0, 21.3; HRMS (ESI) exact mass calcd for C22H28N2NaO6 [M +
Na]+, 439.1845, found 439.1862.
tert-Butyl ((1S,2R)-2-(4-Chlorophenyl)-1-(3,4-dimethoxy-
phenyl)-2-nitroethyl)carbamate (4ak). This compound was pre-
pared according to the general procedure employing catalyst (R,R)-10
(5 mol %) with a 48 h reaction time. Column chromatography (SiO2,
0−5% ethyl acetate in hexanes) afforded the product as a tan crystalline
solid (28.3 mg, 54%) that was found to be 92% ee and 25:1 dr by chiral
HPLC (ChiralPak AD-H, 10% EtOH/hexanes, 1.0 mL/min: tr (anti,
minor) = 13.2 min, tr (syn, major) = 15.8 min, tr (anti, major) = 17.2 min,
1
IR (film) 3378, 3274, 2977, 1698, 1526, 1491 cm−1; H NMR (400
MHz, CDCl3) δ 7.39 (d, J = 8.0 Hz, 2H), 7.21 (d, J = 8.0 Hz, 2H), 6.95
(d, J = 7.2 Hz, 2H), 6.94 (d, J = 7.2 Hz, 2H), 5.46 (d, J = 6.8 Hz, 1H),
4.79 (br t, 1H), 4.22 (br d, 1H), 1.56 (br s, 2H), 1.36 (s, 9H); 13C NMR
(100 MHz, CDCl3) ppm 155.1, 140.8, 133.4, 132.6, 128.7 (2C), 128.3,
121.41, 120.3, 79.8, 59.3, 28.3 (3C); HRMS (ESI) exact mass calcd for
C19H23BrClN2O2 [M + H]+ 425.0631, found 425.0643.
tert-Butyl ((1R,2S)-2-(4-Bromophenyl)-1-(4-chlorophenyl)-2-
(2-isopropoxy-4-methoxybenzamido)ethyl)carbamate (S7).
Amine S6 (383 mg, 900 μmol) and carboxylic acid (189 mg,
900 μmol) were dissolved in CH2Cl2 (4.5 mL), chilled to 0 °C, and
treated with EDC·HCl (224 mg, 1.17 mmol) and DMAP (10 mg,
90 μmol). The reaction mixture was stirred and gradually warmed to
room temperature over 2 h. After 16 h, the mixture was diluted with
water and extracted with dichloromethane. The combined organic layers
were washed with water, saturated aqueous NaHCO3, and once more
with water. The organic layer was dried (MgSO4), filtered, and
concentrated. The residue was washed with a 3/7 dichloromethane/
hexanes mixture and decanted to afford a white solid (438 mg, 79%) that
was >95% pure by 1H NMR: [α]D20 = −17° (c 0.39, CHCl3); mp =223−
225 °C; Rf = 0.9 (10% MeOH/CH2Cl2); IR (film) 3350, 2978, 1685,
1631, 1611, 1530, 1496 cm−1; 1H NMR (400 MHz, CDCl3) δ 8.38 (d,
J = 6.8 Hz, 1H), 8.18 (d, J = 8.8 Hz, 1H), 7.41 (d, J = 8.4 Hz, 2H), 7.21
(d, J = 8.0 Hz, 2H), 6.94 (m, 4H), 6.59 (dd, J = 8.8, 2.4 Hz, 1H), 6.46 (d,
J = 1.2 Hz, 1H), 5.87 (d, J = 4.8 Hz, 1H), 5.75 (d, J = 5.6 Hz, 1H), 5.08
(d, J = 3.6 Hz, 1H), 4.68 (qq, J = 6.0, 6.0 Hz, 1H), 3.84 (s, 3H), 1.38 (s,
9H), 1.26 (m, 6H); 13C NMR (100 MHz, CDCl3) ppm 165.6, 163.7,
157.2, 155.1, 137.3, 134.4, 133.4, 131.5, 128.9, 128.7, 128.4, 121.7, 114.2,
105.3, 100.3, 80.0, 71.5, 59.5, 56.7, 55.5, 31.6, 28.3, 22.6, 22.0, 21.6, 14.1;
HRMS (ESI) exact mass calcd for C30H34BrClN2NaO5 [M + Na]+
639.1237, found 639.1248.
20
tr (syn, minor) = 36.8 min): [α]D = −21° (c 0.36, CHCl3); mp
150−151 °C; Rf = 0.11 (20% EtOAc in hexanes); IR (film) 3383, 2989,
1676, 1595, 1519, 1463, 1423, 1367 cm−1; 1H NMR (400 MHz, CDCl3)
δ 7.52 (d, J = 8.4 Hz, 2H), 7.38 (d, J = 8.4 Hz, 2H), 6.82−6.89 (m, 3H),
5.77 (d, J = 9.2 Hz, 1H), 5.54 (dd, J = 9.4, 9.2 Hz, 1H), 3.87 (br d, 1H),
3.87 (s, 3H), 3.87 (s, 3H), 1.28 (s, 9H); 13C NMR (100 MHz, CDCl3)
ppm 154.2, 149.3, 149.2, 136.3, 130.2, 130.0, 129.5, 128.9, 119.1, 111.3,
110.5, 93.4, 80.5, 55.9, 55.8, 29.6, 28.0; HRMS (ESI) exact mass calcd for
C21H25ClN2NaO6 [M + Na]+ 459.1299; found 459.1305.
tert-Butyl ((1R,2S)-1,2-Bis(3,4-dimethoxyphenyl)-2-
nitroethyl)carbamate (4hk). This compound was prepared accord-
ing to the general procedure employing catalyst (R,R)-10 (5 mol %) with
a 48 h reaction time. Following silica plug filtration, 1H NMR showed >20:1
dr. Column chromatography (SiO2, 10−40% ethyl acetate in hexanes)
afforded the adduct as an off-white crystalline solid (23.0 mg, 72%) that
was found to be 50% ee and 5:1 dr (epimerized on silica) by chiral
HPLC (Chiralcel IA: 12% iPrOH/hexanes, 1.0 mL/min: tr(d2e2 minor/
minor) = 15.4 min, tr(d1e2 major/minor) = 17.8 min, tr(d1e1 major/
major) = 24.8 min, tr(d2e2 minor/minor) = 34.5 min): mp 171 °C dec;
Rf = 0.75 (50% EtOAc/hexanes); IR (film) 3369, 2969, 2930, 2838,
1699, 1553, 1523, 1253 cm−1; 1H NMR (400 MHz, CDCl3) δ 7.15 (s,
1H), 7.08 (dd, J = 8.4, 2.0 Hz, 1H), 6.91−6.83 (m, 4H), 5.73 (d, J = 10.0
Hz, 1H), 5.63 (dd, J = 10.0, 8.4 Hz, 1H), 4.78 (d, J = 9.2 Hz, 1H), 3.91 (s,
3H), 3.89 (s, 3H), 3.88 (s, 3H), 3.86 (s, 3H), 1.28 (s, 9H); 13C NMR
(100 MHz, CDCl3) ppm 154.4, 150.5, 149.2, 149.1 (2C), 130.1, 123.9,
122.2, 119.1, 111.3, 122.2, 119.1, 111.1, 111.0, 110.7, 110.6, 94.2, 80.3,
55.9 (4C), 28.1; HRMS (ESI) exact mass calcd for C23H30N2NaO8 [M +
Na]+ 485.1933, found 485.1958.
tert-Butyl ((1R,2S)-2-(3,4-Dimethoxyphenyl)-2-nitro-1-(m-
tolyl)ethyl)carbamate (4hg). This compound was prepared accord-
ing to the general procedure employing catalyst (R,R)-10 (5 mol %)
with a 72 h reaction time. The reaction precipitate was added to the filter
paper of a Buchner funnel and washed with cold hexanes to afford the
product as a light brown crystalline solid (30 mg, 70%) that was found to
be 78% ee and 1:1 dr (epimerized from 20:1 dr (1H NMR) shortly after
Buchner filtration) determined by chiral HPLC (Chiralcel AD: 10%
iPrOH/hexanes, 1.0 mL/min: tr(d1e1 major/major) = 15.2 min, tr(d1e2
N-((1S,2R)-2-Amino-1-(4-bromophenyl)-2-(4-chlorophenyl)-
ethyl)-2-isopropoxy-4-methoxybenzamide (S8). Amide S7
(374 mg, 605 μmol) was dissolved in dichloromethane (6.0 mL), and
the solution was treated with TFA (1.8 mL, 24 mmol) and stirred at
room temperature for 2 h. The reaction mixture was diluted with
dichloromethane, poured into saturated aqueous NaHCO3, and
extracted with dichloromethane. The combined organic layers were
dried (MgSO4), filtered, and concentrated to a white foam (300 mg,
96%): [α]D20 = −103° (c 1.07, CHCl3); Rf = 0.6 (10% MeOH/CH2Cl2);
1
IR (film) 3371, 2991, 2929, 1643, 1609, 1519, 1498 cm−1; H NMR
(600 MHz, CDCl3) δ 8.89 (d, J = 8.0 Hz, 1H), 8.12 (d, J = 8.8 Hz, 1H),
7.34 (d, J = 8.4 Hz, 2H), 7.23 (d, J = 8.4 Hz, 2H), 7.02 (d, J = 8.4 Hz,
2H), 6.93 (d, J = 8.4 Hz, 2H), 6.55 (dd, J = 8.8, 2.0 Hz, 1H), 6.48 (d, J =
2.0 Hz, 1H), 5.40 (dd, J = 8.0, 8.0 Hz, 1H), 4.75 (qq, J = 6.0, 6.0 Hz, 1H),
4.40 (d, J = 8.8 Hz, 1H), 3.83 (s, 3H), 1.70 (br, 2H), 1.44 (d, J = 6.0 Hz,
3H), 1.43 (d, J = 6.0 Hz, 3H); 13C NMR (150 MHz, CDCl3) ppm 164.6,
163.3, 157.2, 140.7, 137.3, 134.1, 133.1, 131.1, 129.5, 128.4, 128.3, 121.4,
114.9, 105.1, 100.3, 71.5, 58.9, 58.6, 55.5, 22.2, 22.0; HRMS (ESI) exact
mass calcd for C25H26BrClN2NaO3 [M + Na]+ 539.0713, found
539.0696.
N-((1R,2S)-2-(4-Bromophenyl)-1-(4-chlorophenyl)-2-(2-iso-
propoxy-4-methoxybenzamido)ethyl)-3-oxopiperazine-1-car-
boxamide (S9). Amine S8 (267 mg, 516 μmol) was added to carbonyl
diimidazole (109 mg, 671 μmol) in dichloromethane (1.8 mL).
The mixture was stirred at room temperature for 90 min (or until no
starting material remained by TLC), at which point the oxopiperazine
(103 mg, 1.03 μmol) was added. The mixture was stirred for 16 h and
then diluted with dichloromethane and water. The aqueous layer was
extracted with dichloromethane, and the organic layers were combined,
dried (MgSO4), filtered, and concentrated to an off-white oil. Column
chromatography (SiO2, 0−3% methanol in dichloromethane) afforded
major/minor) = 22.4 min, tr(d2e1 minor/major) = 24.8 min, tr(d2e2
minor/minor) = 39.0 min): mp 175−177 °C; Rf = 0.31 (20% EtOAc/
hexanes); IR (film) 3344, 2972, 2931, 1703, 1558, 1524, 1468 cm−1; 1H
NMR (400 MHz, CDCl3) δ 7.23 (d, J = 7.2 Hz, 1H), 7.15−7.08 (m,
5H), 6.85 (d, J = 8.4 Hz, 1H), 5.70 (m, 2H), 4.81 (d, J = 8.4 Hz, 1H),
3.91 (s, 3H), 3.89 (s, 3H), 2.34 (s, 3H), 1.28 (s, 9H); 13C NMR (100
MHz, CDCl3) ppm 154.4, 150.5, 149.0, 138.7, 137.0, 129.5, 128.9,
127.7, 124.0, 122.2, 121.4, 111.1, 111.0, 94.3, 56.0, 28.2, 21.2; HRMS
(ESI) exact mass calcd for C22H28N2NaO6 [M + Na]+, 439.1845, found
439.1862.
tert-Butyl ((1R,2S)-2-Amino-2-(4-bromophenyl)-1-(4-
chlorophenyl)ethyl)carbamate (S6). β-Nitro Boc-amine 4ba
(470 mg, 1.03 mmol) and CoCl2 (134 mg, 1.03 mmol) were added to
6929
dx.doi.org/10.1021/jo501003r | J. Org. Chem. 2014, 79, 6913−6938

The Journal of Organic Chemistry
Article
the urea as a white solid (301 mg, 91%): [α]D20 = +90° (c 0.54, CHCl3);
mp =170 °C (dec.); Rf = 0.36 (10% MeOH/CH2Cl2); IR (film) 3375,
3236, 2980, 1669, 1634, 1606, 1537, 1495 cm−1; 1H NMR (600 MHz,
CDCl3) δ 8.36 (d, J = 7.6 Hz, 1H), 8.25 (d, J = 8.8 Hz, 1H), 7.76 (d, J =
8.8 Hz, 1H), 7.43 (d, J = 8.4 Hz, 2H), 7.16 (d, J = 8.4 Hz, 2H), 6.89 (m,
4H), 6.70 (br s, 1H), 6.60 (dd, J = 8.8, 2.0 Hz, 1H), 6.45 (d, J = 2.0 Hz,
1H), 5.75 (dd, J = 8.0, 2.4 Hz, 1H), 5.10 (dd, J = 2.8, 2.4 Hz, 1H), 4.65
(qq, J = 6.0, 6.0 Hz, 1H), 4.13 (d, J = 2.4 Hz, 2H), 3.85 (s, 3H), 3.71 (m,
1H), 3.59 (m, 1H), 3.38 (m, 2H), 1.19 (d, J = 6.0 Hz, 3H), 1.14 (d, J =
6.0 Hz, 3H); 13C NMR (150 MHz, CDCl3) ppm 167.8, 167.2, 164.0,
157.3, 155.0, 137.0, 136.4, 134.4, 133.3, 131.6, 129.4, 128.7, 128.1, 122.0,
113.4, 105.4, 100.3, 71.5, 61.8, 57.7, 55.6, 47.5, 41.1, 40.0, 22.0, 21.5;
HRMS (ESI) exact mass calcd for C30H32BrClN4NaO5 [M + Na]+
665.1142, found 665.1149.
(MgSO4), filtered, and concentrated. Column chromatography (SiO2,
0−6% methanol in dichloromethane) afforded the amide as a white solid
(112 mg, 68%): [α]D20 = +32° (c 0.65, CHCl3); mp =169 °C; Rf = 0.60
(10% MeOH/CH2Cl2); IR (film) 3367, 2978, 2934, 1638, 1604, 1532,
1492, 1259 cm−1; 1H NMR (400 MHz, CDCl3) δ 8.35 (d, J = 8.0 Hz,
1H), 8.24 (d, J = 8.8 Hz, 1H), 7.71 (d, J = 4.8 Hz, 1H), 7.43 (d, J = 8.4
Hz, 2H), 7.16 (d, J = 8.0 Hz, 2H), 6.90 (d, J = 8.4 Hz, 2H), 6.89 (d, J =
8.4 Hz, 2H), 6.85 (br s, 1H), 6.60 (dd, J = 8.8, 2.0 Hz, 1H), 6.44 (d, J =
2.0 Hz, 1H), 5.76 (dd, J = 8.0, 2.8 Hz, 1H), 5.10 (dd, J = 2.8, 2.0 Hz, 1H),
4.65 (qq, J = 6.0, 6.0 Hz, 1H), 4.10 (d, J = 3.2 Hz, 2H), 3.84 (s, 3H), 3.70
(m, 1H), 3.58 (m, 1H), 3.37 (m, 2H), 1.20 (d, J = 6.0 Hz, 3H), 1.14 (d,
J = 6.0 Hz, 3H); 13C NMR (100 MHz, CDCl3) ppm 167.9, 167.2, 164.0,
157.2, 156.0, 137.1, 136.5, 134.4, 133.3, 131.6, 129.4, 128.7, 128.1, 121.9,
113.5, 105.4, 100.3, 71.5, 61.7, 60.4, 57.7, 55.6, 47.5, 41.1, 40.0, 22.0,
21.5, 21.0, 14.2; HRMS (ESI) exact mass calcd for C30H32BrClN4NaO5
[M + Na]+ 665.1142, found 665.1165.
cis-Imidazoline 11. Tf2O (143 μL, 845 μmol) was added to a stirred
solution of Ph3PO (470 mg, 1.69 mmol) in dichloromethane (1.0 mL)
at 0 °C, and this mixture was stirred for 10 min and then treated with the
cis-amide urea S11 or S8 (272 mg, 422 μmol) as a solution in
dichloromethane (2.0 mL). The mixture was stirred at 0 °C for 1 h prior
to stirring at room temperature for 4 h. The reaction mixture was
quenched with NaHCO3, the aqueous layer was extracted with
dichloromethane, and the combined organic layers were dried
(MgSO4), filtered, and concentrated. Column chromatography (SiO2,
0−2% methanol in dichloromethane) of the residue provided the
product as a white solid (173 mg, 66%): [α]D20 = −69° (c 0.70, CHCl3);
mp 118−120 °C; Rf = 0.39 (10% MeOH/CH2Cl2); IR (film) 3223,
3077, 2980, 2931, 1676, 1613, 1495, 1419 cm−1; 1H NMR (400 MHz,
CDCl3) δ 7.61 (d, J = 8.8 Hz, 1H), 7.24 (d, J = 8.4 Hz, 2H), 7.03 (d, J =
8.4 Hz, 2H), 6.88 (d, J = 8.4 Hz, 2H), 6.87 (d, J = 8.4 Hz, 2H), 6.55 (dd,
J = 8.4, 2.0 Hz, 1H), 6.48 (d, J = 2.4 Hz, 1H), 6.00 (br s, 1H), 5.56 (d, J =
9.6 Hz, 1H), 5.46 (d, J = 9.6 Hz, 1H), 4.61 (qq, J = 6.0, 6.0 Hz, 1H), 3.85
(s, 3H), 3.77 (d, J = 18.0 Hz, 1H), 3.65 (d, J = 18.0 Hz, 1H), 3.88 (m,
1H), 3.22 (m, 1H), 3.01 (m, 2H), 1.39 (d, J = 6.0 Hz, 3H), 1.34 (d, J =
6.0 Hz, 3H); 13C NMR (100 MHz, CDCl3) ppm 166.9, 163.0, 160.2,
157.0, 154.7, 136.5, 135.0, 133.1, 132.1, 130.9, 129.6, 128.4,128.1, 121.0,
113.4, 104.6, 100.1, 71.8, 70.9, 69.1, 55.5, 49.4, 41.8, 40.3, 22.0 (2C);
HRMS (ESI) exact mass calcd for C30H31BrClN4O4 [MH]+ 625.1217,
found 625.1207.
tert-Butyl ((1R,2S)-2-Amino-2-(4-chlorophenyl)-1-(3-
(trifluoromethoxy)phenyl)ethyl)carbamate (S17). β-Nitro Boc-
amine ent-4ab (140 mg, 304 μmol) and CoCl2 (46.0 mg, 304 μmol)
were added to methanol (1.2 mL) in a flask and chilled to 0 °C before
NaBH4 (57 mg, 1.5 mmol) was added in three portions over 5 h. The
reaction mixture was stirred at 0 °C for an additional 15 min before the
mixture was quenched with saturated aqueous NH4Cl. The reaction
mixture was adjusted to pH 10 with concentrated aqueous NH4OH, and
the aqueous layer was extracted with ethyl acetate. The combined
organic layers were dried (MgSO4), filtered, and concentrated. Column
chromatography (SiO2, 40−60% ethyl acetate in hexanes) afforded the
product as a white foam (60 mg, 46%) in about 15:1 dr (by 1H NMR):
Rf = 0.40 (50% EtOAc/hexanes); IR (film) 3378, 3302, 2977, 2929,
1699 cm−1; 1H NMR (400 MHz, CDCl3) δ 7.28 (m, 1H), 7.23 (d, J = 8.0
Hz, 2H), 7.08 (d, J = 7.6 Hz, 1H), 6.98 (d, J = 8.0 Hz, 2H), 6.94 (m, 1H),
6.86 (s, 1H), 5.56 (d, J = 8.0 Hz, 1H), 4.84 (br dd, 1H), 4.26 (br d, 1H),
1.50 (br m, 2H), 1.36 (s, 9H); 13C NMR (100 MHz, CDCl3) ppm 155.1,
149.0, 140.1, 133.4, 130.6, 129.4, 128.4, 128.2, 125.9, 121.6, 120.3 (q,
1JCF = 251 Hz), 120.0, 119.9, 119.1 79.9, 59.1, 28.2; HRMS (ESI) exact
tert-Butyl ((1S,2R)-2-Amino-1-(4-bromophenyl)-2-(4-
chlorophenyl)ethyl)carbamate (S10). β-Nitro Boc-amine 4ac
(265 mg, 581 μmol) and CoCl2 (75.4 mg, 581 μmol) were added to
methanol (3 mL) in a flask and chilled to 0 °C before NaBH4 (110 mg,
2.91 mmol) was added in three portions over 45 min. The reaction
mixture was stirred at 0 °C for an additional 15 min before the mixture
was quenched with saturated aqueous NH4Cl. The reaction mixture was
adjusted to pH 10 with concentrated aqueous NH4OH, and the aqueous
layer was extracted with ethyl acetate. The combined organic layers were
dried (MgSO4), filtered, and concentrated to a white foam (260 mg,
99%): [α]D20 = +40° (c 0.27, CHCl3); Rf = 0.31 (50% EtOAc/hexanes);
1
IR (film) 3371, 2976, 2982, 2859, 1697, 1489, 1366 cm−1; H NMR
(400 MHz, CDCl3) δ 7.36 (d, J = 8.4 Hz, 2H), 7.25 (d, J = 8.8 Hz, 2H),
7.00 (d, J = 8.0 Hz, 2H), 6.87 (d, J = 8.0 Hz, 2H), 5.45 (br s, 1H), 4.77
(br s, 1H), 4.23 (s, 1H), 1.36 (s, 9H), 1.25 (d, J = 6.4 Hz, 2H); 13C NMR
(100 MHz, CDCl3) ppm 155.0, 140.3, 133.3, 131.5, 131.2, 129.1, 128.4,
128.3, 121.5, 59.1, 28.3 (3C); HRMS (ESI) exact mass calcd for
C19H23BrClN2O2 [M + H]+ 425.0631, found 425.0641.
N-((1R,2S)-2-Amino-2-(4-bromophenyl)-1-(4-chlorophenyl)-
ethyl)-3-oxopiperazine-1-carboxamide (S11). Amine S10 (241 mg,
566 μmol) was added to carbonyl diimidazole (119 mg, 736 μmol) in
dichloromethane (2.0 mL). The mixture was stirred at room
temperature for 3 h (or until no starting material remained by TLC),
at which point the oxopiperazine (113 mg, 1.13 mmol) was added. The
mixture was stirred for 16 h and then diluted with dichloromethane
and water. The aqueous layer was extracted with dichloromethane, and
the organic layers were combined, dried (MgSO4), filtered, and
concentrated to an off-white solid. The solid was washed with 1/1
dichloromethane/hexanes (6 mL), and the wash layer was decanted to
afford the desired product as a 1/1 mixture with imidazole. This was
used without further purification. The urea (230 mg, 417 μmol) was
dissolved in dichloromethane (5.0 mL), and the solution was treated
with TFA (1.26 mL, 16.0 mmol) and stirred at room temperature for 3 h.
The reaction mixture was diluted with dichloromethane, poured into
saturated aqueous NaHCO3, and extracted with dichloromethane. The
combined organic layers were dried (MgSO4), filtered, and concentrated
20
to a brown oil (170 mg, 67% over two steps): [α]D = +32° (c 0.24,
CHCl3); Rf = 0.23 (10% MeOH/CH2Cl2); IR (film) 3344, 3262, 3069,
2924, 2848, 1675, 1537, 1496 cm−1; 1H NMR (600 MHz, CDCl3) δ 7.40
(d, J = 8.0 Hz, 2H), 7.19 (d, J = 8.0 Hz, 2H), 6.92 (d, J = 8.4 Hz, 2H),
6.92 (d, J = 8.4 Hz, 2H), 6.84 (br s, 1H), 5.89 (d, J = 7.2 Hz, 1H), 5.00 (t,
J = 6.4 Hz, 1H), 4.26 (d, J = 4.8 Hz, 1H), 4.05 (s, 2H), 3.60 (d, J = 2.8 Hz,
2H), 3.33 (br d, 2H), 1.85 (br s, 2H); 13C NMR (150 MHz, CDCl3)
ppm 167.3, 155.7, 140.8, 136.7, 133.4, 131.4, 128.8, 128.5 (2C), 128.3,
121.5 (2C), 59.3, 59.1, 47.6, 40.9, 39.7, 29.7; HRMS (ESI) exact mass
calcd for C19H21BrClN4O2 [M + H]+ 451.0536, found 451.0536.
N-((1R,2S)-2-(4-Bromophenyl)-1-(4-chlorophenyl)-2-(2-iso-
propoxy-4-methoxybenzamido)ethyl)-3-oxopiperazine-1-car-
boxamide (S12). Amine S11 (116 mg, 257 μmol) and carboxylic acid
(54.0 mg, 257 μmol) were dissolved in dichloromethane (1.3 mL),
chilled to 0 °C, and treated with EDC·HCl (64.0 mg, 334 μmol) and
DMAP (3.1 mg, 26 μmol). The reaction mixture was stirred and
gradually warmed to room temperature over 2 h. After 5 h, the mixture
was diluted with water and extracted with dichloromethane. The
combined organic layers were washed with water, saturated aqueous
NaHCO3, and once more with water. The organic layer was dried
mass calcd for C20H23ClF3N2O3 [M + H]+ 431.1349, found 431.1366.
tert-Butyl ((1R,2S)-2-(4-Chlorophenyl)-2-(3-oxopiperazine-1-
carboxamido)-1-(3-(trifluoromethoxy)phenyl)ethyl)carbamate
(S18). Amine S17 (60 mg, 139 μmol) was added to carbonyl
diimidazole (29.4 mg, 181 μmol) in dichloromethane (0.5 mL). The
mixture was stirred at room temperature for 90 min (or until no starting
material remained by TLC), at which point the oxopiperazine (27.8 mg,
278 μmol) was added. The mixture was stirred for 16 h and then
diluted with dichloromethane and water. The aqueous layer was ex-
tracted with dichloromethane, and the organic layers were combined,
dried (MgSO4), filtered, and concentrated to an off-white oil. The
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residue was washed with hexanes (4 mL) and the wash layer was
decanted to afford the desired product as a 1:1 mixture with imidazole.
This was used without further purification. The urea (47 mg, 84 μmol)
was dissolved in dichloromethane (2.0 mL), and the solution was treated
with TFA (180 μL, 3.3 mmol) and stirred at room temperature
overnight. The reaction mixture was diluted with dichloromethane,
poured into saturated aqueous NaHCO3, and extracted with dichloro-
methane. The combined organic layers were dried (MgSO4), filtered,
and concentrated to an oil. The residue was washed with hexanes, and
the wash layer was decanted to afford the desired product as a yellow
foam (40 mg, 63% over two steps) in about 20:1 dr (by 1H NMR): Rf =
0.1 (5% MeOH/CH2Cl2); IR (film) 3344, 3262, 2924, 1668 cm−1; 1H
NMR (600 MHz, CDCl3) δ 7.31 (t, J = 7.8 Hz, 1H), 7.18 (d, J = 8.4 Hz,
2H), 7.09 (d, J = 7.8 Hz, 1H), 7.04 (m, 2H), 6.90 (d, J = 8.4 Hz, 2H),
6.88 (s, 1H), 6.00 (d, J = 7.2 Hz, 1H), 5.03 (dd, J = 12.6, 1.8 Hz, 1H),
4.33 (d, J = 4.8 Hz, 1H), 4.07 (dd, J = 17.4, 12.6 Hz, 2H), 3.60 (m, 2H),
3.31 (m, 2H), 1.24 (br m, 2H); 13C NMR (150 MHz, CDCl3) ppm
167.5, 155.7, 149.1, 144.5, 136.6, 133.4, 129.8, 128.8 (2C), 128.3 (2C),
125.2, 120.1, 119.5, 59.4, 59.0, 47.5, 40.9, 39.6, 14.1; HRMS (ESI) exact
mass calcd for C20H21ClF3N4O3 [M + H]+ 457.1254, found 457.1268.
cis-Imidazoline 15. Tf2O (16 μL, 96 μmol) was added to a stirred
solution of Ph3PO (53 mg, 191 μmol) in dichloromethane (300 μL)
at 0 °C, and this mixture was stirred for 10 min and then treated with cis-
amide urea 19 (30.2 mg, 48.8 μmol) as a solution in dichloromethane
(800 μL). The mixture was stirred at 0 °C for 1 h prior to stirring at room
temperature for 4 h. The reaction mixture was quenched with NaHCO3,
the aqueous layer was extracted with dichloromethane, and the
combined organic layers were dried (MgSO4), filtered, and concen-
trated. Column chromatography (SiO2, 0−4% methanol in dichloro-
methane) of the residue provided the product as a white solid (21.0 mg,
73%): [α]D20 = −1.7° (c 0.21, CHCl3); mp 125−126 °C; Rf = 0.26 (5%
MeOH/CH2Cl2); IR (film) 3216, 2980, 2932, 1683, 1614, 1440 cm−1;
1H NMR (400 MHz, CDCl3) δ 7.60 (d, J = 8.8 Hz, 1H), 7.13 (t, J = 8.0
Hz, 1H), 7.00 (d, J = 8.4 Hz, 2H), 6.94 (t, J = 8.0 Hz, 2H), 6.87 (s, 1H),
6.84 (d, J = 8.4 Hz, 2H), 6.56 (dd, J = 8.4, 2.0 Hz, 1H), 6.49 (d, J = 2.0
Hz, 1H), 6.40 (s, 1H), 5.59 (d. J = 10.0 Hz, 1H), 5.52 (d, J = 10.0 Hz,
1H), 4.61 (qq, J = 6.0, 6.0 Hz, 1H), 3.83 (s, 3H), 3.83 (d, J = 18.0 Hz,
1H), 3.62 (d, J = 18.0 Hz, 1H), 3.42 (m, 1H), 3.18 (m, 1H), 3.00 (m,
2H), 1.38 (d, J = 6.0 Hz, 3H), 1.33 (d, J = 6.0 Hz, 3H); 13C NMR (100
61.8, 57.7, 55.6, 47.5, 41.1, 40.0, 21.8, 21.4; HRMS (ESI) exact mass
calcd for C31H33ClF3N4O6 [M + H]+ 649.2041, found 649.2023.
cis-Imidazoline 21.44 In a microwave vial under an inert atmo-
sphere was placed Pd(PPh3)4 (4.7 mg, 4.1 μmol). The vial was charged
with K2CO3 (13.3 mg, 96.0 μmol), boronic ester 20 (10.0 mg,
48.0 μmol), and cis-imidazoline 11 (20.0 mg, 32.0 μmol). The vial was
sealed, evacuated, and back-filled with argon. This process was repeated
three times. A 5/1 mixture of dioxanes in water (865 μL) was then added
via syringe under argon. The mixture was stirred for 20 h at 80 °C
(conventional heating), and the solvent was then evaporated after
cooling. Column chromatography (SiO2, 0−5% methanol in dichloro-
methane) of the residue afforded the adduct as an off-white foam
(13 mg, 62%): [α]D20 = −37° (c 0.27, CHCl3); Rf = 0.68 (10% MeOH/
CH2Cl2); IR (film) 3259, 2923, 2852, 1674, 1607, 1423 cm−1; 1H NMR
(400 MHz, CDCl3) δ 7.65 (d, J = 8.8 Hz, 1H), 7.48 (d, J = 1.6 Hz, 1H),
7.14 (d, J = 8.0 Hz, 2H), 7.06 (d, J = 8.0 Hz, 2H), 7.00 (d, J = 8.4 Hz,
2H), 6.89 (d, J = 8.4 Hz, 2H), 6.57 (dd, J = 8.4, 2.0 Hz, 1H), 6.49 (d, J =
2.0 Hz, 1H), 6.24 (d, J = 2.0 Hz, 1H), 5.86 (br s, 1H), 5.62 (d, J = 9.6 Hz,
1H), 5.58 (d, J = 9.6 Hz, 1H), 4.61 (qq, J = 6.0, 6.0 Hz, 1H), 3.85 (s, 3H),
3.76 (s, 3H), 3.73 (m, 2H), 3.38 (m, 1H), 3.28 (m, 1H), 3.04 (m, 2H),
1.40 (d, J = 6.0 Hz, 3H), 1.62 (d, J = 6.0 Hz, 3H); 13C NMR (100 MHz,
CDCl3) ppm 166.5, 163.0, 160.3, 157.1, 154.9, 143.2, 138.4, 138.0,
135.3, 133.1, 132.2, 129.5, 128.4, 128.2 (2C), 127.9, 105.8, 104.6, 100.2,
72.2, 71.1, 69.3, 68.4, 63.7, 55.6, 49.8, 41.7, 40.5, 37.3, 29.7, 22.1; HRMS
(ESI) exact mass calcd for C34H36ClN6O4 [M + H]+ 627.2487, found
627.2466.
tert-Butyl ((1S,2R)-2-Amino-2-(4-chlorophenyl)-1-(4-
fluorophenyl)ethyl)carbamate (S19). β-Nitro Boc-amine 4ad
(301 mg, 760 μmol), methanol (2.9 mL), and cobalt(II) chloride
(49.3 mg, 379 μmol) were combined and stirred. The solution was
cooled to 0 °C, and sodium borohydride (431 mg, 11.2 mmol) was
added in five portions over 1 h. The reaction mixture was stirred at 0 °C
for an additional 30 min before the mixture was quenched with saturated
aqueous NH4Cl. The reaction mixture was adjusted to pH 10 with
concentrated aqueous NH4OH. The mixture was placed on a glass frit
and washed with water, and the aqueous layer was collected. The
remaining solid was thoroughly washed with CH2Cl2 and collected in a
separate flask. The organic layers were dried (MgSO4), filtered, and
concentrated to afford a white solid (221 mg, 75%): [α]D20 = −45° (c
0.84, CHCl3); mp 144−146 °C; Rf = 0.36 (50% EtOAc in hexanes); IR
(film) 3371, 2970, 2922, 2355, 1692, 1602, 1512 cm−1; 1H NMR (400
MHz, CD3OD) δ7.58 (d, J = 8.4 Hz, 2H), 7.02−6.92 (m, 6H), 4.81
(br m, 1H), 4.24 (br d, 1H), 1.48−1.38 (m, 12H); 13C NMR (100 MHz,
MHz, CDCl3) ppm 166.8, 163.0, 160.6, 157.1, 154.7, 148.9, 134.8,
1
133.3, 132.1, 129.2, 128.2, 128.1, 126.4, 121.6, 120.6, 120.4 (q, JCF
=
256 Hz), 119.9, 133.4, 104.6, 104.1, 100.2, 71.8, 71.1, 69.1, 63.9, 55.5,
49.3, 42.0, 40.5, 22.0 (2C), 18.0, 15.3; HRMS (ESI) exact mass calcd for
C31H31ClF3N4O5 [M + H]+ 631.1935, found 631.1917.
1
CD3OD) ppm 163.7 (d, JCF = 244 Hz), 157.2, 142.2, 137.6, 134.2,
130.7 (d, 3JCF = 8.0 Hz), 130.4, 129.3, 116.2 (d, 2JCF = 22.0 Hz), 80.2,
61.5, 60.9, 28.6; LRMS (ESI) exact mass calcd for C19H22ClFN2O2
[M + H]+ 365.135, found 365.57,
N-((1S,2R)-1-(4-Chlorophenyl)-2-(2-isopropoxy-4-methoxy-
benzamido)-2-(3-(trifluoromethoxy)phenyl)ethyl)-3-oxopiper-
azine-1-carboxamide (19). N-((1R,2S)-2-Amino-1-(4-chlorophenyl)-
2-(3-(trifluoromethoxy)phenyl)ethyl)-3-oxopiperazine-1-carboxamide
(35 mg, 76 μmol) and carboxylic acid 18 (16 mg, 77 μmol) were
dissolved in dichloromethane (385 μL), and the solution was chilled to
0 °C and treated with EDC·HCl (19 mg, 99 μmol) and DMAP (1 mg,
7.7 μmol). The reaction mixture was stirred and gradually warmed to
room temperature over 2 h. After 17 h, the mixture was diluted with
water and extracted with dichloromethane. The combined organic layers
were washed with water, saturated aqueous NaHCO3, and once more
with water. The organic layer was dried (MgSO4), filtered, and con-
centrated. Column chromatography (SiO2, 0−4% methanol in
dichloromethane) afforded a single diastereomer of the amide as a
yellow oil (42 mg, 87%): [α]D20 = +84° (c 1.01, CHCl3); Rf = 0.2 (5%
MeOH/CH2Cl2); IR (film) 3368, 3257, 2980, 2931, 1676, 1641, 1537,
1503 cm−1; 1H NMR (400 MHz, CDCl3) δ 8.38 (d, J = 8.0 Hz, 1H), 8.24
(d, J = 8.8 Hz, 1H), 7.66 (d, J = 5.2 Hz, 1H), 7.37 (t, J = 8.0 Hz, 1H), 7.17
(m, 1H), 7.16 (d, J = 8.0 Hz, 2H), 7.09 (d, J = 7.6 Hz, 1H), 6.88 (d, J =
8.0 Hz, 2H), 6.87 (m, 1H), 6.83 (br d, 1H), 6.60 (dd, J = 8.8, 2.0 Hz,
1H), 6.45 (d, J = 2.0 Hz, 1H), 5.85 (dd, J = 8.0, 2.4 Hz, 1H), 5.14 (dd, J =
2.4, 2.4 Hz, 1H), (qq, J = 6.0, 6.0 Hz, 1H), 4.12 (br m, 2H), 3.85 (s, 3H),
3.70 (m, 1H), 3.58 (m, 1H), 3.38 (br m, 2H), 1.19 (d, J = 6.0 Hz, 3H),
1.16 (d, J = 6.0 Hz, 3H); 13C NMR (100 MHz, CDCl3) ppm 167.9,
167.2, 157.3, 155.9, 149.2, 140.5, 136.3, 134.5, 133.4, 130.0, 129.2, 128.1,
125.8, 121.0 (q, 1JCF = 254 Hz), 120.5, 119.8, 113.4, 105.4, 100.3, 71.6,
tert-Butyl ((1S,2R)-2-(4-Chlorophenyl)-1-(4-fluorophenyl)-2-
(3-oxopiperazine-1-carboxamido)ethyl)carbamate (S20).
Amine S19 (210 mg, 575 μmol), dichloromethane (2.9 mL), and
carbonyl diimidazole (112 mg, 689 μmol) were combined, and the
mixture was stirred at room temperature for 1 h before adding oxo-
piperazine (115 mg, 1.15 mmol). The resulting mixture was stirred for
5 h before quenching with water and extracting with dichloromethane.
The organic layers were combined, dried (MgSO4), filtered, and
concentrated to afford a white solid (166 mg, 54%): [α]D20 = +16° (c
0.09, CH3COCH3); Mp: 216−218 °C; Rf = 0.54 (10% MeOH in
CH2Cl2); IR (film) 3379 (br), 2981, 1505, 1682, 1608 cm−1; 1H NMR
(400 MHz, CD3OD) δ 7.68 (s, 1H), 7.45−7.40 (m, 4H), 7.32 (d, J = 8.4
Hz, 2H), 7.05 (dd, J = 8.8 Hz, 8.0 Hz, 4H), 5.06 (d, J = 10.8 Hz, 1H),
4.97 (d, J = 10.8 Hz, 1H), 3.90 (d, J = 17.6 Hz, 1H), 3.72 (d, J = 17.6 Hz,
1H), 3.62−3.42 (m, 1H), 3.37−3.36 (m, 1H), 3.10 (m, 2H), 1.25 (s,
9H); 13C NMR (100 MHz, CD3OD) ppm 169.9, 163.5 (d, 1JCF = 243
Hz), 157.9, 157.3, 140.9, 138.2, 136.2, 134.2, 130.7, 130.6 (d, 3JCF = 8.0
Hz), 129.2, 116.0 (d, 2JCF = 21 Hz), 80.3, 59.5, 58.5, 48.2, 41.33, 41.26,
28.6; HRMS (ESI) exact mass cald for C24H28ClFN4NaO4 [M + Na]+
513.1681, found 513.1704.
N-((1R,2S)-2-Amino-1-(4-chlorophenyl)-2-(4-fluorophenyl)-
ethyl)-3-oxopiperazine-1-carboxamide (S21). Boc-protected urea
S20 (150 mg, 306 μmol) was dissolved in dichloromethane (3.0 mL),
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and the solution was treated with TFA (702 μL, 9.80 mmol) and stirred
at room temperature overnight. The reaction mixture was diluted with
dichloromethane and poured into saturated aqueous NaHCO3. The
aqueous layer was extracted with dichloromethane, and the organic
layers were combined, dried (MgSO4), filtered, and concentrated to an
off-white oil (100 mg, 84%): [α]D20 = −1.8° (c 0.61, MeOH); Rf = 0.36
(10% MeOH in CH2Cl2); IR (film) 3352 br, 3067, 2936, 2890, 1664,
1518 cm−1; 1H NMR (400 MHz, CDCl3) δ 7.17 (d, J = 8.4 Hz, 2H), 7.03
(m, 6H), 5.97 (d, J = 7.2 Hz, 1H), 4.99 (dd, J = 7.2, 6.0 Hz, 1H), 4.28 (d,
J = 5.6 Hz, 1H), 4.01 (d, J = 5.6 Hz, 2H), 3.60−3.56 (m, 2H), 3.29 (br m,
2H), 1.26 (m, 2H); 13C NMR (100 MHz, CDCl3) ppm 167.5, 162.1 (d,
1JCF = 243 Hz), 155.7, 137.5 (d, 4JCF = 3 Hz), 137.0, 133.3, 128.9, 128.4,
9.08 mmol) was added in two portions over 1 h. The reaction mixture
was stirred at 0 °C for an additional 15 min before the mixture was
quenched with saturated aqueous NH4Cl. The reaction mixture was
adjusted to pH 10 with concentrated aqueous NH4OH, and the aqueous
layer was extracted with EtOAc. The combined organic layers were dried
(MgSO4), filtered, and concentrated. Column chromatography (SiO2,
20−40% ethyl acetate in hexanes) afforded the product as a white oil
1
(172 mg, 43%) in 6:1 dr (by H NMR): Rf = 0.71 (50% EtOAc/
hexanes); IR (film) 3378, 2975, 2920, 1691, 1527, 1486 cm−1; 1H NMR
(400 MHz, CDCl3) δ 7.34 (dd, J = 4.0, 4.0 Hz, 1H), 7.25 (d, J = 7.6 Hz,
2H), 7.20 (d, J = 4.8 Hz, 1H), 7.03, (d, J = 7.6 Hz, 2H), 6.92 (t, J = 8.8
Hz, 1H), 5.50 (d, J = 6.4 Hz, 1H), 4.79 (br d, 1H), 4.46 (d, J = 6.4 Hz,
1H), 1.40 (br m, 2H), 1.33 (s, 9H); 13C NMR (100 MHz, CDCl3) ppm
128.3 (d, 3JCF = 9 Hz), 115.1 (d, 2JCF = 21 Hz), 59.4, 58.9, 47.5, 40.8,
39.6; HRMS (ESI) exact mass cald for C19H20ClFN4NaO2 [M + Na]+
413.1157, found 413.1145.
1
3
160.6 (d, JCF = 255 Hz), 133.6, 131.9, 131.8, 131.1 (d, JCF = 4 Hz),
128.6, 128.5, 128.2, 117.2 (d, 2JCF = 24 Hz), 116.8 (d, 3JCF = 4 Hz), 79.0,
58.6, 53.4, 28.2; HRMS (ESI) exact mass calcd for C19H22BrClFN2O2
[M + H]+ 443.0537, found 443.0547.
N-((1R,2S)-1-(4-Chlorophenyl)-2-(4-fluorophenyl)-2-(2-iso-
propoxy-4-methoxybenzamido)ethyl)-3-oxopiperazine-1-car-
boxamide (S22). Amine S21 (80.0 mg, 205 μmol) and 2-isopropoxy-
4-methoxybenzoic acid (43.1 mg, 205 μmol) were combined in
dichloromethane (1.0 mL). The solution was chilled to 0 °C, and
DMAP (2.5 mg, 21 μmol) and EDC·HCl (51.0 mg, 266 μmol) were
added. The mixture was gradually warmed to room temperature and
stirred for 24 h before it was diluted with dichloromethane and water.
The aqueous layer was extracted with dichloromethane three times. The
combined organic layers were dried (MgSO4), filtered, and concen-
trated. The resulting residue was purified via column chromatography
(0−6% methanol in dichloromethane) to afford an off-white oil
(74 mg, 62%). [α]D20 = +61° (c 0.36, CHCl3); Rf = 0.56 (10% MeOH in
CH2Cl2); IR (film) 3369, 3259, 2975, 2926, 1666, 1646, 1542, 1493
cm−1; 1H NMR (400 MHz, CDCl3) δ 8.35 (d, J = 7.6 Hz, 1H), 8.22 (d,
J = 8.8 Hz, 1H), 7.74 (d, J = 5.2 Hz, 1H), 7.27 (br m, 1H), 7.15 (d, J = 8.4
Hz, 2H), 7.00 (m, 4H), 6.91 (d, J = 8.4 Hz, 2H), 6.58 (dd, J = 9.2, 8.8 Hz,
1H), 6.44 (d, J = 2.0 Hz, 1H), 5.77 (dd, J = 8.0, 7.6 Hz, 1H), 5.08 (dd, J =
3.2, 3.2 Hz, 1H), 4.64 (qq, J = 6.0, 6.0 Hz, 1H), 4.10 (s, 2H), 3.83 (s,
3H), 3.66 (m, 1H), 3.56 (m, 1H), 3.35 (br m, 2H), 1.19 (d, J = 6.0 Hz,
3H), 1.13 (d, J = 6.0 Hz, 3H) 13C NMR (100 MHz, CDCl3) ppm 168.1,
tert-Butyl ((1R,2S)-2-(5-Bromo-2-fluorophenyl)-1-(4-chloro-
phenyl)-2-(2-isopropoxy-4-methoxybenzamido)ethyl)-
carbamate (S14). Amine S13 (172 mg, 388 μmol) and carboxylic acid
(81.6 mg, 388 μmol) were dissolved in dichloromethane (1.75 mL) at
room temperature. The solution was chilled to 0 °C, and EDC·HCl
(96.6 mg, 504 μmol) and DMAP (4.8 mg, 39 μmol) were added. The
reaction mixture was stirred and gradually warmed to room temperature
over 2 h. After 17 h, the reaction mixture was diluted with water and
extracted with dichloromethane. The combined organic layers were
washed with water, saturated aqueous NaHCO3, and once more with
water. The organic layer was dried (MgSO4), filtered, and concentrated.
Column chromatography (SiO2, 20−30% ethyl acetate in hexanes)
afforded the amide as a clear foam (213 mg, 87%): Rf = 0.77 (50%
EtOAc/hexanes); IR (film) 3373, 3318, 2980, 2925, 2247, 1714, 1645,
1604, 1536 cm−1; 1H NMR (400 MHz, CDCl3) δ 8.48 (d, J = 9.2 Hz,
1H), 8.13 (d, J = 9.2 Hz, 1H), 7.37 (m, 1H), 7.23 (d, J = 8.4 Hz, 2H),
7.17 (d, J = 7.7 Hz, 1H), 7.06 (d, J = 7.6 Hz, 1H), 6.97 (t, J = 8.8 Hz, 1H),
6.54 (dd, J = 9.2, 1.6 Hz, 1H), 6.44 (s, 1H), 5.97 (dd, J = 9.2, 9.2 Hz, 1H),
5.74 (m, 1H), 5.08 (m, 1H), 4.69 (qq, J = 6.0, 6.0 Hz, 1H), 3.82 (s, 3H),
1.32 (br s, 16H); 13C NMR (100 MHz, CDCl3) ppm 165.3, 163.7, 157.2
(d, 1JCF = 244 Hz), 134.4, 133.6, 132.3 (2C), 132.2, 128.7, 128.6, 128.5
(d, 3JCF = 4 Hz), 117.6 (d, 2JCF = 22 Hz), 116.5 (d, 3JCF = 4 Hz), 114.0,
105.5, 100.1, 77.2, 71.5, 55.5, 28.1, 21.8, 21.7; HRMS (ESI) exact mass
calcd for C30H33BrClFN2NaO5 [M + Na]+ 657.1143, found 657.1113.
N-((1S,2R)-2-Amino-1-(5-bromo-2-fluorophenyl)-2-(4-
chlorophenyl)ethyl)-2-isopropoxy-4-methoxybenzamide
(S15). Amide S14 (210 mg, 330 μmol) was dissolved in dichloro-
methane (3.0 mL) and treated with TFA (758 μL, 9.91 mmol). The
mixture was stirred at room temperature for 3 h and then diluted with
dichloromethane, poured into saturated aqueous NaHCO3, and
extracted with dichloromethane. The combined organic layers were
dried (MgSO4), filtered, and concentrated to a yellow oil. Column
chromatography (SiO2, 30−50% ethyl acetate in hexanes) afforded the
product as a foam (153 mg, 87%) and >20:1 dr by 1H NMR: Rf = 0.15
(50% EtOAc/hexanes); IR (film) 3382, 2980, 2945, 1648, 1606,
1495 cm−1; 1H NMR (400 MHz, CDCl3) δ 8.69 (d, J = 8.8 Hz, 1H), 8.09
(d, J = 8.8 Hz, 1H), 7.41, (dd, J = 6.4, 2.0 Hz, 1H), 7.34 (m, 1H), 7.23 (d,
J = 8.4 Hz, 2H), 7.10 (d, J = 8.4 Hz, 2H), 6.88 (t, J = 8.8 Hz, 1H), 6.53
(dd, J = 8.8, 2.0 Hz, 1H), 6.45 (d, J = 2.0 Hz, 1H), 5.71 (dd, J = 9.2, 1.6
Hz, 1H), 4.73 (qq, J = 6.0, 6.0 Hz, 1H), 4.43 (d, J = 6.4 Hz, 1H), 3.82 (s,
3H), 1.42 (d, J = 6.0 Hz, 3H), 1.41 (d, J = 6.0 Hz, 3H), 1.36 (d, J = 5.6
Hz, 2H); 13C NMR (100 MHz, CDCl3) ppm 164.8, 163.4, 160.8 (d,
1JCF = 245 Hz), 157.2, 139.9, 134.2, 133.4, 132.5 (d, 3JCF = 4 Hz), 132.0
1
167.0, 163.9, 162.3 (d, JCF = 244 Hz), 157.2, 155.9, 136.7, 134.2 (d,
2JCF = 27 Hz), 134.0, 133.2, 129.4, 128.8, 128.0, 115.3 (d, 2JCF = 21 Hz),
113.5, 105.4, 100.3, 71.4, 61.7, 57.5, 55.0, 47.4, 40.9, 40.0, 21.9, 21.5;
HRMS (ESI) exact mass calcd for C30H33ClFN4O5[M + H]+ 583.2124,
found 583.2134.
cis-Imidazoline 22. Triphenylphosphine oxide (136 mg, 488 μmol)
and dichloromethane (200 μL) were placed in a flame-dried flask. The
solution was chilled to 0 °C, treated with triflic anhydride (41 μL,
244 μmol), and stirred for 10 min. cis-Amide urea S22 (71 mg,
122 μmol) as a solution in dichloromethane (800 μL) was placed in the
reaction flask and stirred for 1 h at 0 °C. The mixture was warmed to
room temperature and stirred for 3 h more. The solution was diluted
with dichloromethane and quenched with saturated aqueous NaHCO3.
The mixture was extracted with dichloromethane, and the combined
organic layers were dried (MgSO4), filtered, and concentrated. Purifica-
tion via column chromatography (0−5% methanol in dichloromethane)
20
yielded an off-white foam (60 mg, 88%): [α]D = +137° (c 0.28,
CHCl3); Rf = 0.33 (5% MeOH in CH2Cl2); IR (film) 3217, 1982, 1926,
1680, 1611, 1514, 1424 cm−1; 1H NMR (400 MHz, CDCl3) δ 7.60 (d,
J = 8.4 Hz, 1H), 7.00 (d, J = 8.4 Hz, 2H), 6.95−6.92 (m, 2H), 6.88−6.84
(m, 3H), 6.78 (dd, J = 8.8, 8.4 Hz, 2H), 6.53 (dd, J = 8.4, 8.4 Hz, 1H),
6.46 (dd, J = 2.0 Hz, 1H), 5.53 (d, J = 10.0 Hz, 1H), 5.48 (d, J = 10.0 Hz,
1H), 4.59 (qq, J = 6.0, 6.0 Hz, 1H), 3.82 (s, 3H), 3.73 (d, J = 18.4 Hz,
1H), 3.62 (d, J = 18.4 Hz, 1H), 3.35 (m, 1H), 3.18 (m, 1H), 2.95 (br m,
2H), 1.37 (d, J = 6.0 Hz, 3H), 1.32 (d, J = 6.0 Hz, 3H); 13C NMR (100
MHz, CDCl3) 167.0, 163.9, 161.9 (d, 1JCF = 244 Hz ppm), 160.0, 156.9,
154.8, 135.1, 133.1 (d, 4JCF = 3 Hz), 133.0, 132.2, 129.3 (d, 3JCF = 8 Hz),
(2C), 128.9, 128.8, 128.5, 128.4, 117.5 (d, 2JCF = 24 Hz), 116.6 (d, 3JCF
=
4 Hz), 114.6, 105.8, 104.1, 100.2, 77.2, 71.4, 63.8, 58.4, 55.5, 54.0, 21.9
(2C); HRMS (ESI) exact mass calcd for C25H26BrClFN2O3 [M + H]+
535.0799, found 535.0790.
N-((1R,2S)-2-(5-Bromo-2-fluorophenyl)-1-(4-chlorophenyl)-
2-(2-isopropoxy-4-methoxybenzamido)ethyl)-3-oxopipera-
zine-1-carboxamide (S16). Amine S15 (150 mg, 277 μmol) was
added to carbonyl diimidazole (53.0 mg, 332 μmol) in dichloromethane
(6.5 mL). The mixture was stirred at room temperature for 3 h, or until
no starting material remained by TLC, at which point oxopiperazine
2
128.3, 128.0, 114.6 (d, JCF = 21 Hz), 113.5, 104.5, 100.1, 71.7, 70.9,
69.2, 55.5, 49.4, 41.8, 40.3, 22.0 (2C); HRMS (ESI) exact mass calcd for
C30H31ClFN4O4 [M + H]+ 565.2018, found 565.1992.
tert-Butyl ((1R,2S)-2-Amino-2-(5-bromo-2-fluorophenyl)-1-
(4-chlorophenyl)ethyl)carbamate (S13). β-Nitro Boc-amine 4da
(430 mg, 0.908 μmol) and CoCl2 (118 mg, 0.908 μmol) were added to
methanol (3.7 mL) in a flask and chilled to 0 °C before NaBH4 (343 mg,
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(55.0 mg, 554 μmol) was added. The mixture was stirred for 16 h. The
reaction mixture was concentrated and purified by column chromatog-
raphy (SiO2, 40−100% ethyl acetate in hexanes) to afford the product as
a white solid (68 mg, 40%): [α]D20 = +90° (c 0.20, CHCl3); mp 150−
152 °C (dec.); Rf = 0.61 (10% MeOH/CH2Cl2); IR (film) 3371, 3260,
3074, 2977, 2928, 1650, 1602, 1533 cm−1; 1H NMR (400 MHz, CDCl3)
δ 8.49 (d, J = 8.8 Hz, 1H), 8.15 (d, J = 8.8 Hz, 1H), 7.39 (m, 1H), 7.31 (d,
J = 9.6 Hz, 1H), 7.19 (d, J = 8.0 Hz, 2H), 7.03 (d, J = 8.0 Hz, 2H), 6.97
(m 3H), 6.55 (dd, J = 9.2, 1.6 Hz, 1H), 6.44 (d, J = 1.6 Hz, 1H), 6.07 (dd,
J = 9.2, 9.2 Hz, 1H), 5.13 (m, 1H), 4.67 (qq, J = 6.0, 6.0 Hz, 1H), 4.10 (d,
J = 1.6 Hz, 2H), 3.83 (s, 3H), 3.68 (m, 1H), 3.56 (m, 1H), 3.38 (br m,
2H), 1.26 (dd, J = 6.0, 6.0 Hz, 6H); 13C NMR (100 MHz, CDCl3) ppm
167.9, 166.6, 163.9, 159.1 (d, 1JCF = 246 Hz), 157.3, 155.8, 137.0, 134.4,
133.5, 132.4 (2C), 131.1 (d, 3JCF = 4 Hz), 129.2, 128.3, 128.1, 117.7 (d,
2JCF = 24 Hz), 116.4 (d, 3JCF = 4 Hz), 113.4, 105.2, 100.2, 71.6, 60.1, 55.5,
52.2, 47.4, 41.1, 39.9, 21.9, 21.6; HRMS (ESI) exact mass calcd for
C30H31BrClFN4NaO5 [M + Na]+ 683.1048, found 683.1021.
(2.1 mL) was added CDI (103 mg, 635 μmol) at room temperature
under nitrogen, the reaction mixture was stirred for 1 h, piperazin-2-one
(85 mg, 846 μmol) was then added, and this mixture was stirred for 15 h
at room temperature. The solvent was removed, and the crude product
was purified by column chromatography (SiO2, 0−10% methanol
in dichloromethane) to give a white solid (160 mg, 58%): 1H NMR (400
MHz, CDCl3) δ 8.38 (d, J = 7.9 Hz, 1H), 8.18 (dd, J = 8.5, 1.1 Hz, 1H),
7.54 (d, J = 5.2 Hz, 1H), 7.33−7.28 (m, 2H), 7.25−7.22 (m, 1H), 7.21−
7.17 (m, 2H), 7.11 (dt, J = 1.9, 0.9 Hz, 1H), 7.06−7.00 (m, 1H), 6.92 (d,
J = 2.0 Hz, 1H), 6.90−6.84 (m, 2H), 6.13 (s, 1H), 5.82−5.72 (m, 1H),
5.17 (dd, J = 5.4, 2.4 Hz, 1H), 4.79−4.62 (m, J = 6.2, 5.8 Hz, 1H), 4.14 (t,
J = 1.4 Hz, 2H), 3.74 (dt, J = 13.6, 4.8 Hz, 1H), 3.60 (ddd, J = 13.5, 6.1,
4.7 Hz, 1H), 3.48−3.35 (m, 2H), 1.25−1.16 (m, 6H); HRMS (ESI) exact
mass calcd for C29H30BrCl2N4O4 [M + H]+ 647.0829, found 647.0826.
cis-Imidazoline 24. To triphenylphosphine oxide (251 mg,
0.901 mmol) in dichloromethane (2.5 mL) was added trifluorometha-
nesulfonic anhydride (0.076 mL, 0.450 mmol)) at 0 °C, the reaction
mixture was stirred for 10 min, amide-urea S31 (146 mg, 0.225 mmol) in
dichloromethane (2 mL) was then added, and the reaction mixture was
stirred at 0 °C for 1 h and warmed to room temperature before the
addition of saturated aqueous NaHCO3. The dichloromethane layer was
separated, and the aqueous layer was extracted with dichloromethane.
The combined organic layers were washed with brine, dried (Na2SO4),
filtered, and concentrated. The crude product was purified by column
chromatography (SiO2, 0−7% methanol in dichloromethane) to give a
white solid (98 mg, 69%): [α]23D = −81.9° (c 0.5, CH3OH); IR (film)
3263, 2979, 1680, 1589, 1488,1406 cm−1; 1H NMR (400 MHz, CDCl3)
δ 7.56 (d, J = 8.1 Hz, 1H), 7.19 (dd, J = 8.1, 1.6 Hz, 1H), 7.11 (d, J = 1.5
Hz, 1H), 7.09−7.01 (m, 4H), 6.98 (s, 1H), 6.87 (dd, J = 7.7, 6.1 Hz, 3H),
6.03 (s, 1H), 5.68−5.50 (m, 2H), 4.74−4.56 (m, 1H), 3.92−3.65 (m,
3H), 3.35 (s, 1H), 3.25 (ddd, J = 13.5, 7.2, 4.2 Hz, 1H), 3.14−2.95 (m,
2H), 1.41 (d, J = 6.1 Hz, 3H), 1.37 (d, J = 6.0 Hz, 3H); 13C NMR (101
MHz, CDCl3) δ 166.7, 160.1, 156.2, 154.7, 139.4, 134.7, 133.9, 133.5,
132.0, 129.1, 128.4, 128.2, 127.9, 127.4, 126.0, 125.9, 123.7, 120.1, 116.3,
72.4, 71.6, 69.0, 49.5, 41.7, 40.3, 36.7, 24.7, 22.0 (2C); HRMS (ESI)
exact mass calcd for C29H28BrCl2N4O3 [M + H]+ 629.0722, found
629.0716.
cis-Imidazoline 23. Tf2O (35.8 μL, 212 μmol) was added to a
stirred solution of Ph3PO (118 mg, 424 μmol) in dichloromethane
(300 μL) at 0 °C. The mixture was stirred for 10 min before cis-amide
urea S16 (70 mg, 106 μmol) was added as a solution in dichloromethane
(800 μL), and the mixture was stirred at 0 °C and warmed to room tem-
perature over 3 h. The reaction mixture was quenched with NaHCO3
at room temperature, and the aqueous layer was extracted with
dichloromethane. The combined organic layers were dried (MgSO4),
filtered, and concentrated. Column chromatography (SiO2, 0−4%
methanol in dichloromethane) of the residue provided the product as a
white solid (52.0 mg, 78%): [α]D20 = −57° (c 0.71, CHCl3); mp 123−
124 °C; Rf = 0.57 (10% MeOH/CH2Cl2); IR (film) 3229, 2981, 2933,
2361, 1680, 1604 cm−1; 1H NMR (400 MHz, CDCl3) δ 7.66 (d, J = 8.0
Hz, 2H), 7.52 (d, J = 6.8 Hz, 1H), 7.16 (m, 1H), 7.02 (s, 4H), 6.64 (s,
1H), 6.56 (d, J = 8.4 Hz, 1H), 6.47 (s, 1H), 5.76 (d, J = 10.0 Hz, 1H),
5.55 (d, J = 10.0 Hz, 1H), 4.59 (qq, J = 6.0, 6.0 Hz, 1H), 3.84 (s, 3H),
3.80 (d, J = 18.0 Hz, 1H), 3.58 (d, J = 18.0 Hz, 1H), 3.42 (m, 1H), 3.12
(m 1H), 3.02 (br m, 2H), 1.36 (d, J = 6.0 Hz, 3H), 1.27 (d, J = 6.0 Hz,
3H); 13C NMR (100 MHz, CDCl3) ppm 166.9, 163.1, 160.6, 158.7 (d,
1JCF = 244 Hz), 156.9, 154.9, 153.3, 133.4, 132.4, 132.1 (2C), 131.9,
3
N-((1S,2R)-2-Amino-1-(3-chlorophenyl)-2-(4-chlorophenyl)-
ethyl)-4-cyano-2-isopropoxybenzamide (S32). To amine S27
(186 mg, 905 μmol) in dichloromethane (4.0 mL) were added EDC·
HCl (225 mg, 1.18 mmol) and DMAP (11.05 mg, 90 μmol) at 0 °C, and
the reaction mixture was gradually warmed to room temperature over
16 h. The reaction mixture was diluted with water and extracted with
dichloromethane. The organic layers were combined, washed with
brine, dried (Na2SO4), filtered, and concentrated to give a white solid.
The crude product was triturated with dichloromethane and hexanes,
filtered, and dried under vacuum to give a white solid (428 mg, 83%),
which was used for the next step directly. To tert-butyl ((1R,2S)-2-(3-
chlorophenyl)-1-(4-chlorophenyl)-2-(4-cyano-2-isopropoxybenzamido)-
ethyl)carbamate (390 mg, 686 μmol) in dichloromethane (6.5 mL) was
added TFA (2.12 mL, 27.5 mmol), and the reaction mixture was stirred
at room temperature for 16 h. The reaction mixture was then poured
into saturated aqueous NaHCO3 and extracted with dichloromethane.
The combined organic layers were washed with brine, dried (Na2SO4),
filtered, and concentrated. The residue was purified by column
chromatography (SiO2, 0−7% methanol in dichloromethane) to give
131.7 (2C), 128.5, 128.4, 128.3, 128.1, 127.9, 116.5 (d, JCF = 4 Hz),
116.1 (d, 2JCF = 24 Hz), 113.4, 104.6, 100.0, 70.8, 68.1, 66.6, 55.5, 49.7,
42.1, 40.3, 22.1, 22.0; HRMS (ESI) exact mass calcd for
C30H30BrClFN4O4 [M + H]+ 643.1123, found 643.1127.
N-((1S,2R)-2-Amino-1-(3-chlorophenyl)-2-(4-chlorophenyl)-
ethyl)-4-bromo-2-isopropoxybenzamide (S30). To amine S27
(298 mg, 782 μmol) and 4-bromo-2-isopropoxybenzoic acid (202 mg,
782 μmol) in dichloromethane (4.0 mL) were added EDC·HCl
(195 mg, 1.02 mmol) and DMAP (9.55 mg, 78 μmol) at 0 °C, and the
reaction mixture was gradually warmed to room temperature over
16 h. The reaction mixture was diluted with water and extracted with
dichloromethane. The combined organic layers were washed with brine,
dried (Na2SO4), filtered, and concentrated to give a white solid. The
crude product was triturated with dichloromethane and hexanes,
filtered, and dried under vacuum to give a white solid (438 mg, 90%)
which was used for the next step directly. To tert-butyl ((1R,2S)-2-(4-
bromo-2-isopropoxybenzamido)-2-(3-chlorophenyl)-1-(4-chlorophenyl)-
ethyl)carbamate (240 mg, 386 μmol) in dichloromethane (3.8 mL) was
added TFA (1.191 mL, 15.46 mmol), and the reaction mixture was
stirred at room temperature for 16 h. The reaction mixture was then
poured into saturated aqueous NaHCO3 and extracted with dichloro-
methane. The organic layers were combined, washed with brine, dried
(Na2SO4), filtered, and concentrated. The residue was purified by
column chromatography (SiO2, 0−7% methanol in dichloromethane)
23.3
a white solid (290 mg, 90%): [α]D = −21.0° (c 0.275, CH3OH);
mp =165−166 °C; IR (film) 3378, 2980, 2935, 2231, 1655, 1603, 1573,
1557, 1515, 1489, 1411 cm−1; 1H NMR (400 MHz, CDCl3) δ 8.97 (d,
J = 8.0 Hz, 1H), 8.24 (dd, J = 8.1, 1.4 Hz, 1H), 7.32 (dd, J = 8.1, 1.4 Hz,
1H), 7.28−7.19 (m, 4H), 7.18−7.11 (m, 2H), 7.04−6.97 (m, 2H), 6.81
(d, J = 7.6 Hz, 1H), 5.39 (dd, J = 8.0, 4.9 Hz, 1H), 4.83 (p, J = 6.1 Hz,
1H), 4.39 (d, J = 4.7 Hz, 1H), 1.55−1.50 (m, 6H), 1.45 (d, J = 11.3 Hz,
2H); 13C NMR (101 MHz, CDCl3) δ 163.0, 155.8, 140.3, 139.6, 134.2,
133.6, 133.4, 129.3, 128.5, 128.2, 127.9, 127.5, 126.4, 126.2, 124.5, 118.1,
116.7, 115.8, 72.6, 58.9, 58.9, 22.03, 21.96; HRMS (ESI) exact mass
calcd for C25H24Cl2N3O2 [M + H]+ 468.1247, found 468.1239.
1
to give a white foam (151 mg, 75%): H NMR (400 MHz, CDCl3) δ
8.88 (d, J = 8.1 Hz, 1H), 8.02 (d, J = 8.4 Hz, 1H), 7.26−7.21 (m, 3H),
7.21−7.15 (m, 2H), 7.14 (d, J = 2.0 Hz, 3H), 7.01 (d, J = 8.4 Hz, 2H),
6.84 (d, J = 7.6 Hz, 1H), 5.42 (dd, J = 8.2, 4.9 Hz, 1H), 4.87−4.73 (m,
1H), 4.40 (d, J = 4.9 Hz, 1H), 1.52−1.41 (m, 7H); HRMS (ESI) exact
mass calcd for C24H24BrCl2N2O2 [M + H]+ 521.0400, found 521.0392.
N-((1R,2S)-2-(4-Bromo-2-isopropoxybenzamido)-2-(3-chlor-
ophenyl)-1-(4-chlorophenyl)ethyl)-3- oxopiperazine-1-carbox-
amide (S31). To amine S30 (221 mg, 423 μmol) in dichloromethane
N-((1R,2S)-2-(3-Chlorophenyl)-1-(4-chlorophenyl)-2-(4-
cyano-2-isopropoxybenzamido)ethyl)-3-oxopiperazine-1-car-
boxamide (S33). To amine S32 (252 mg, 538 μmol) in dichloromethane
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(3.0 mL) was added CDI (131 mg, 807 μmol) at room temperature
under N2. The reaction mixture was stirred for 1 h, piperazin-2-one (108
mg, 1.08 mmol) was then added, and this mixture was stirred for 15 h at
room temperature. The solvent was removed, and the crude product was
purified by column chromatography (SiO2, 0−10% methanol in dichlo-
romethane) to give a white solid (292 mg, 91%). [α]D23.5 = 16.4° (c 0.30,
CH3OH); mp 196−197 °C; IR (film) 3314, 2981, 2231, 1637, 1538,
under high vacuum to yield the title compound as a light yellow solid
(217 mg, 54%): mp 181−184 °C; Rf = 0.36 (10% MeOH/CH2Cl2); IR
(film) 3366, 2980, 2930, 1678, 1632, 1526, 1250, 1168; 1H NMR (400
MHz, DMSO-d6) δ 7.88 (br d, 1 H), 7.49 (d, J = 8.0 Hz, 2 H), 7.44−7.27
(m, 6 H), 7.03 (br m, 1 H), 6.87 (d, J = 8.0 Hz, 1 H), 4.93 (m, 2 H), 3.76
(d, J = 16.8 Hz, 1 H), 3.53 (d, J = 18 Hz, 1 H), 3.27 (m, 2 H), 2.92 (br m,
2 H), 1.15 (s, 9 H); 13C NMR (100 MHz, DMSO-d6) ppm 166.9, 155.8,
154.9, 145.5, 141.4, 131.9, 129.9, 129.8, 128.2, 124.7, 118.4, 115.0, 114.8,
113.7, 78.2, 58.0, 56.6, 55.3, 47.6, 28.4; HRMS (ESI) exact mass calcd for
C24H28ClFN4NaO4 [M + Na]+ 513.1681, found 513.1704.
tert-Butyl ((1S,2R)-2-Amino-1-(4-chlorophenyl)-2-(3-
fluorophenyl)ethyl)carbamate (S25). The urea S24 (178 mg,
0.36 mmol) was dissolved in methanol (16 mL) at room temperature
and the solution then cooled to 0 °C. Acetyl chloride (206 μL, 2.90
mmol) was added via syringe to the cold solution, and the reaction
mixture was stirred under an Ar atmosphere for 15 h, at which point the
solvent was removed by rotary evaporation and high vacuum. The solid
was redissolved in dichloromethane and NaHCO3 and extracted once.
The aqueous layer was back-extracted 10 times with dichloromethane to
afford the deprotected amine as a light yellow solid (84 mg, 60%): mp
139−142 °C; Rf = 0.21 (10% MeOH/CH2Cl2); IR (film) 3329, 3054,
2926, 1669, 1636, 1542, 1343, 1245 cm−1; 1H NMR (400 MHz, DMSO-
d6) δ 7.93 (br s, 1 H), 7.42 (d, J = 8.4 Hz, 2 H), 7.34 (m, 3 H), 7.25 (d, J =
10.8 Hz, 1 H), 7.17 (d, J = 7.6 Hz, 1 H), 7.05 (m, 3 H), 6.75 (d, J = 8.8
Hz, 1 H), 4.73 (dd, J = 9.2, 9.2 Hz, 1 H), 4.10 (d, J = 9.6 Hz, 1 H), 3.85
(m, 1 H), 3.61 (m, 1 H), 2.99 (br m, 2 H), 1.93 (br m, 2 H); 13C NMR
(100 MHz, DMSO-d6) ppm 166.7, 161.2, 156.0, 145.6, 144.1, 131.4,
129.9, 129.6, 128.0, 124.7, 115.0, 114.8, 114.0, 113.8, 60.8, 58.9, 47.7;
HRMS (ESI) exact mass calcd for C19H21ClFN4O2 [M + H]+ 391.1337,
found 391.1342.
N-((1R,2S)-2-(4-Chlorophenyl)-1-(3-fluorophenyl)-2-(2-iso-
propoxy-4-methoxybenzamido)ethyl)-3-oxopiperazine-1-car-
boxamide (S26). In a glass vial equipped with a magnetic stir bar and
argon balloon were placed amine S25 (49 mg, 0125 mmol), carboxylic
acid (26.3 mg, 0.125 mmol), and dichloromethane (1.0 mL). The
mixture was cooled to 0 °C with stirring before addition of EDC·HCl
(31 mg, 0.163 mmol) and DMAP (1.6 mg, 13 μmol). The reaction
mixture was stirred for 18 h before dilution with dichloromethane and
aqueous extraction. The combined organic layers were dried with
MgSO4 and concentrated to a light yellow solid (62 mg, 85%). The solid
was redissolved in CH2Cl2 and purified by column chromatography
(2−10% MeOH/CH2Cl2, 55%): mp 123−136 °C; Rf = 0.27 (10%
MeOH/CH2Cl2), IR (film) 3369, 2933, 1639, 1605, 1533, 1493,
1257 cm−1; 1H NMR (400 MHz, CDCl3) δ 8.43 (d, J = 8.4 Hz, 1 H),
8.27 (d, J = 9.2 Hz, 1 H), 7.71 (d, J = 4.8 Hz), 7.28 (s, 1 H), 7.15 (m, 1
H), 6.55 (d, J = 8.4 Hz, 2 H), 6.77 (d, J = 10.0 Hz, 1 H), 6.66 (d, J = 7.2
Hz, 1 H), 6.62 (dd, J = 9.2, 2.4 Hz, 1 H), 6.46 (d, J = 2.0 Hz, 1 H), 6.43 (s,
1 H), 5.80 (dd, J = 8.0, 2.4 Hz, 1 H), 5.13 (dd, J = 4.8, 2.8 Hz, 1 H), 4.67
(qq, J = 6.0, 6.0 Hz, 1 H), 4.14 (s, 2 H), 3.85 (s, 3 H), 3.70 (m, 1 H), 3.60
(m, 1 H), 3.41 (br m, 2 H), 1.22 (d, J = 6.0 Hz, 3 H), 1.15 (d, J = 6.0 Hz, 3
H); 13C NMR (100 MHz, CDCl3) ppm 168.0, 167.1, 163.9, 162.1 (d,
1JCF = 243 Hz), 157.2, 156.0, 140.8, 140.7, 136.6, 134.4, 133.8, 129.3,
129.2, 128.6, 128.4, 124.1, 114.9, 114.6, 114.5, 114.3, 113.5, 105.3, 100.3,
71.4, 61.8, 57.5, 55.5, 47.4, 41.0, 40.0, 22.0, 21.3; HRMS (ESI) exact
mass calcd for C30H33ClFN4O5 [M + H]+ 583.2124, found 583.2126.
cis-Imidazoline 26. Triphenylphosphine oxide (92 mg, 0.330
mmol) was dissolved in dichloromethane (0.65 mL) at room tem-
perature. Triflic anhydride (27.8 μL, 0.165 mmol) was delivered via
syringe, and the solution was stirred for 30 min. The cis-amide urea
(48 mg, 0.082 mmol) was delivered as a solution in dichloromethane
(0.65 mL, 1.30 mL total), and the reaction mixture was stirred for 18 h.
The reaction mixture was diluted with dichloromethane, quenched with
saturated aqueous NaHCO3, and extracted once. The aqueous layer was
back-extracted with dichloromethane, and the organic layers were
combined, dried (MgSO4), filtered, and concentrated to a yellow-orange
foam. This material was redissolved in dichloromethane and purified by
column chromatography (SiO2, 0−4% methanol in dichloromethane)
to afford the desired product as a light yellow solid (30 mg, 65%) in 9:1
dr: mp 112−114 °C; Rf = 0.40 (10% MeOH/CH2Cl2); IR (film) 3223,
2979, 2929, 1676, 1607, 1424, 1340, 1280; 1H NMR (400 MHz, CDCl3)
1
1492, 1413 cm−1; H NMR (400 MHz, CDCl3) δ 8.41 (dd, J = 12.2,
8.0 Hz, 2H), 7.38 (dd, J = 8.1, 1.1 Hz, 1H), 7.30 (dt, J = 9.1, 5.3 Hz, 3H),
7.21 (d, J = 8.1 Hz, 3H), 7.05 (d, J = 6.3 Hz, 1H), 6.95 (s, 1H), 6.89 (d,
J = 8.4 Hz, 2H), 6.28 (s,1H), 5.76 (dd, J = 8.0, 2.5 Hz, 1H), 5.21 (dd, J =
5.3, 2.6 Hz, 1H), 4.74 (p, J = 6.0 Hz, 1H), 4.12 (s, 2H), 3.73(dt, J = 13.0,
4.9 Hz, 1H), 3.68−3.51 (m, 1H), 3.41 (s, 2H), 1.35−1.13 (m, 6H); 13C
NMR (126 MHz, CDCl3) δ 167.3, 165.5, 155.8, 139.5, 136.0, 134.7,
133.9, 133.7, 130.1, 129.2, 128.5, 128.3, 126.9, 125.4, 124.6, 124.5, 117.8,
116.7, 116.7, 72.8, 61.5, 58.4, 47.6, 41.2, 39.9, 21.8, 21.4; HRMS (ESI)
exact mass calcd for C30H30Cl2N5O4 [M + H]+ 594.1677, found
594.1674.
cis-Imidazoline 25. To triphenylphosphine oxide (324 mg,
1.164 mmol) in dichloromethane (2.5 mL) was added trifluorometha-
nesulfonic anhydride (0.099 mL, 0.586 mmol) at 0 °C, the reaction
mixture was stirred for 10 min, amide-urea S33 (170 mg, 0.286 mmol) in
dichloromethane (1.5 mL) was then added, and the reaction mixture
was stirred at 0 °C for 1 h and then warmed to room temperature before
the addition of saturated aqueous NaHCO3. The dichloromethane layer
was separated, and the aqueous layer was extracted with dichloro-
methane. The combined organic layers were washed with brine, dried
(Na2SO4), filtered, and concentrated. The crude product was purified by
column chromatography (SiO2, 0−7% MeOH in dichloromethane) to
give a white solid (135 mg, 82%): [α]D23 = −85.1° (c 0.5, CH3OH); IR
(film) 3231, 2981, 2230, 1676, 1599, 1573, 1541, 1493, 1414 cm−1; 1H
NMR (400 MHz, CDCl3) δ 7.81 (dd, J = 7.8, 1.2 Hz, 1H), 7.35 (dt, J =
7.9, 1.4 Hz, 1H), 7.20 (s, 1H), 7.11−6.96 (m, 5H), 6.94−6.81 (m, 3H),
6.75 (d, J = 3.4 Hz, 1H), 5.75−5.53 (m, 2H), 4.69 (hept, J = 6.2 Hz, 1H),
3.81 (q, J = 17.7 Hz, 2H), 3.29 (q, J = 5.8 Hz, 2H), 3.10 (dq, J = 12.3, 4.7,
4.0 Hz, 1H), 3.06−2.95 (m, 1H), 1.45−1.35 (m, 6H); 13C NMR (101
MHz, CDCl3) δ 166.4, 159.9, 155.6, 154.7, 139.2, 134.4, 134.0, 133.8,
131.7, 129.2, 128.4, 128.3, 127.9, 127.5, 126.3, 125.9, 124.2, 118.2, 115.8,
115.1, 73.0, 71.9, 69.0, 49.6, 41.4, 40.4, 21.9 (2C); HRMS (ESI) exact
mass calcd for C30H28Cl2N5O3 [M + H]+ 576.1569, found 576.1572.
tert-Butyl ((1S,2R)-2-Amino-1-(4-chlorophenyl)-2-(3-
fluorophenyl)ethyl)carbamate (S23). β-Nitro Boc-amine ent-4ea
(500 mg, 1.27 mmol) and CoCl2 (165 mg, 1.27 mmol) were dissolved in
methanol (16.7 mL) at room temperature and then cooled to 0 °C with
stirring. NaBH4 (716 mg, 19.0 mmol) was added in three portions over
1 h. The reaction mixture was then stirred for 1 h and acidified to pH 2
with 1 M HCl. The solution was readjusted to pH 10 with 1 M aqueous
NH4OH and filtered through a glass frit, washing with deionized water.
The solid on the filter was washed heavily with dichloromethane, and the
filtrate was collected, dried (MgSO4), filtered, and concentrated to yield
the product as a white solid (355 mg, 77%): mp 141−143 °C; Rf = 0.51
(10% MeOH/CH2Cl2); IR (film) 3380, 2981, 2935, 1682, 1523, 1490,
1249, 1167 cm−1; 1H NMR (400 MHz, CDCl3) δ 7.27 (d, J = 6.5 Hz, 1
H), 7.23 (d, J = 8.3 Hz, 3 H), 6.95 (m, 3 H), 6.99 (d, J = 7.7 Hz, 1 H),
6.83 (d, J = 9.5 Hz), 5.55 (br d, J = 6.5 Hz, 1 H), 4.84 (br dd, 1 H), 4.27
(br d, 1 H), 1.39 (br s, 9 H); 13C NMR (100 MHz, CDCl3) ppm 162.6
(d, 1JCF = 244 Hz), 155.0, 144.7, 144.6, 133.3, 129.8, 129.7, 128.6, 128.2,
127.7, 122.5, 114.5, 114.3, 113.9, 113.7, 79.7, 59.3, 28.2; HRMS (ESI)
exact mass calcd for C19H23ClFN2O2 [M + H]+ 365.1432, found
365.1448.
tert-Butyl ((1S,2R)-1-(4-Chlorophenyl)-2-(3-fluorophenyl)-2-
(3-oxopiperazine-1-carboxamido)ethyl)carbamate (S24).
Amine S23 (300 mg, 0.82 mmol) was dissolved in dichloromethane
(9.7 mL) at room temperature. To the solution was added CDI (174 mg,
1.07 mmol) with stirring under argon. Oxopiperazine (164 mg,
1.64 mmol) was delivered after 1 h, and the reaction mixture was
stirred for 18 h. The reaction mixture was then concentrated by rotary
evaporation, triturated with dichloromethane, and filtered through
qualitative filter paper, washing with a small amount of dichloro-
methane. The product was removed from the filter paper and dried
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δ 7.62 (d, J = 8.4 Hz, 1 H), 7.06 (d, J = 8.4 Hz, 2 H), 6.99 (m, 1 H), 6.94
(d, J = 8.0 Hz), 6.76 (m, 2 H), 6.62 (d, J = 8.0 Hz), 6.58 (s, 1 H), 6.55
(dd, J = 8.4, 2.0 Hz, 1 H), 6.48 (d, J = 2.0 Hz, 1 H), 5.55 (d, J = 9.6 Hz, 1
H), 5.49 (d, J = 9.6 Hz, 1 H), 4.61 (qq, J = 6.0, 6.0 Hz, 1 H), 3.84 (s, 3 H),
3.80 (d, J = 18.4 Hz, 1 H), 3.60 (d, J = 18.0 Hz, 1 H), 3.44 (m, 1 H), 3.15
(m, 1 H), 2.99 (m, 2 H), 1.39 (d, J = 6.0 Hz, 3 H), 1.33 (d, J = 6.0 Hz, 3
7.75 (d, J = 5.0 Hz, 1H), 7.45 (dt, J = 8.2, 1.4 Hz, 1H), 7.23 (d,
J = 8.3 Hz, 1H), 7.21−7.16 (m, 2H), 7.08 (dd, J = 6.9, 1.3 Hz, 2H),
6.90−6.85 (m, 2H), 6.62 (dd, J = 8.9, 2.3 Hz, 1H), 6.50−6.40 (m, 2H),
5.79 (dd, J = 8.1, 2.5 Hz, 1H), 5.13 (dd, J = 5.0, 2.5 Hz, 1H), 4.66 (hept,
J = 6.0 Hz, 1H), 4.15 (d, J = 1.7 Hz, 2H), 3.86 (s, 3H), 3.73 (ddd, J =
13.3, 5.9, 4.1 Hz, 1H), 3.60 (ddd, J = 13.3, 6.4, 4.6 Hz, 1H), 3.44−3.38
(m, 2H), 1.22−1.18 (m, 6H); HRMS (ESI) exact mass calcd for
C30H33BrClN4O5 [M + H]+ 643.1325, found 643.1309.
cis-Imidazoline 27. To triphenylphosphine oxide (185 mg, 0.665
mmol) in dichloromethane (1.3 mL) was added trifluoromethanesul-
fonic anhydride (0.056 mL, 0.332 mmol) at 0 °C, the reaction mixture
was stirred at 0 °C for 10 min, amide-urea S39 (107 mg, 0.166 mmol) in
dichloromethane (1 mL) was then added, and the reaction mixture was
stirred at 0 °C for 1 h and then allowed to warmed to room temperature
before the addition of aqueous NaHCO3. The dichloromethane layer
was separated, and the aqueous layer was extracted with dichloro-
methane. The combined dichloromethane layers were washed with
brine, dried (Na2SO4), filtered, and concentrated. The crude product
H); 13C NMR (100 MHz, CDCl3) ppm 166.9, 163.0, 162.5 (d, 1JCF
=
244 Hz), 160.2, 157.0, 154.8, 139.2, 139.1, 135.9, 132.8, 132.3, 129.5,
129.4, 129.1, 128.4, 127.8, 122.7, 114.4, 114.2, 114.1, 113.8, 113.3, 104.5,
100.0, 71.9, 70.9, 69.3, 55.5, 53.4, 49.5, 42.0, 40.4, 29.6, 22.0, 21.7;
HRMS (ESI) exact mass calcd for C30H31ClFN4O4 [M + H]+ 565.2018,
found 565.2023.
tert-Butyl ((1R,2S)-2-Amino-2-(3-bromophenyl)-1-(4-
chlorophenyl)ethyl)carbamate (S37). In a 100 mL flask was placed
β-nitro Boc-amine 4ga (700 mg, 1.54 mmol) in MeOH (15 mL), the
reaction mixture was stirred at room temperature, and then cobalt(II)
chloride (199 mg, 1.54 mmol) was added. The purple solution was
cooled to 0 °C, and then sodium borohydride (872 mg, 23.0 mmol) was
added in three portions over 45 min. The reaction mixture was stirred
at 0 °C for 75 min and then quenched with saturated aqueous NH4Cl.
The solution pH was adjusted to 10 with concentrated NH4OH. The
aqueous layer was extracted with ethyl acetate, and the combined
organic layers were washed with brine, dried (Na2SO4), filtered, and
concentrated to give a white solid (615 mg, 94%): [α]D22.8 = −5.4° (c
0.36, CH3OH); mp 158−159 °C; IR (film) 3373, 2981, 1683, 1594,
1570, 1524, 1493 cm−1; 1H NMR (400 MHz, CDCl3) δ 7.38 (dt, J = 8.1,
1.3 Hz, 1H), 7.27 (s, 1H), 7.25−7.20 (m, 2H), 7.14 (t, J = 7.8 Hz, 1H),
6.99 (dt, J = 7.8, 1.3 Hz, 1H), 6.94 (d, J = 8.1 Hz, 2H), 5.47 (s, 1H), 4.80
(s, 1H), 4.21 (d, J = 5.6 Hz, 1H), 1.37 (s, 11H); 13C NMR (126 MHz,
CDCl3) δ 155.0, 144.4, 136.7, 133.4, 130.7, 130.1, 129.9, 128.8, 128.3,
125.5, 122.5, 79.9, 59.4, 28.3; HRMS (ESI) exact mass calcd for
C19H23BrClN2O2 [M + H]+ 425.0633, found 425.0634.
N-((1S,2R)-2-Amino-1-(3-bromophenyl)-2-(4-chlorophenyl)-
ethyl)-2-isopropoxy-4-methoxybenzamide (S38). To amine S37
(350 mg, 0.822 mmol) and 2-isopropoxy-4-methoxybenzoic acid
(173 mg, 822 μmol) in dichloromethane (4.1 mL) were added EDC·
HCl (205 mg, 1.07 mmol) and DMAP (10.0 mg, 820 μmol) at 0 °C, and
the reaction mixture was gradually warmed to room temperature over
16 h. The reaction mixture was diluted with water and extracted with
dichloromethane. The organic layers were combined, washed with
brine, dried (Na2SO4), filtered, and concentrated to give a white solid.
The crude product was triturated with dichloromethane and hexanes,
filtered, and dried under vacuum to give a white solid (500 mg, 98%),
which was used for the next step directly. To tert-butyl ((1R,2S)-2-
(3-bromophenyl)-1-(4-chlorophenyl)-2-(2-isopropoxy-4-
methoxybenzamido)ethyl)carbamate (330 mg, 534 μmol) in dichloro-
methane (5.0 mL) was added TFA (1.65 mL, 21.4 mmol) at room
temperature, and the reaction mixture was stirred under N2 for 16 h. The
reaction mixture was poured into saturated aqueous NaHCO3 and
extracted with dichloromethane. The organic layer was washed with
brine, dried (Na2SO4), filtered, and concentrated to afford a yellow oil.
This oil was purified by column chromatography (SiO2, 0−10%
methanol in dichloromethane) to give a white solid (202 mg, 73%): 1H
NMR (400 MHz, CDCl3) δ 8.83 (d, J = 8.2 Hz, 1H), 8.13 (d, J = 8.8 Hz,
1H), 7.36 (ddd, J = 7.9, 2.0, 1.0 Hz, 1H), 7.31 (t, J = 1.8 Hz, 1H), 7.26−
7.22 (m, 2H), 7.08 (t, J = 7.8 Hz, 1H), 7.06−7.00 (m, 2H), 6.96−6.89
(m, 1H), 6.56 (dd, J = 8.8, 2.3 Hz, 1H), 6.49 (d, J = 2.3 Hz, 1H), 5.45
(dd, J = 8.3, 5.0 Hz, 1H), 4.76 (p, J = 6.1 Hz, 1H), 4.40 (d, J = 5.0 Hz,
1H), 3.84 (s, 3H), 1.57−1.38 (m, 8H); HRMS (ESI) exact mass calcd
for C25H27BrClN2O3 [M + H]+ 517.0895, found 517.0882.
was purified by column chromatography (SiO2, 0−7% methanol in
23.3
dichloromethane) to give a white solid (95 mg, 91%): [α]D
=
−110.2° (c 0.575, CH3OH); IR (film) 3224, 2979, 2936,1675, 1608,
1493,1424 cm−1; 1H NMR (400 MHz, CDCl3) δ 7.64 (d, J = 8.5 Hz,
1H), 7.21 (dt, J = 7.7, 1.7 Hz, 1H), 7.11 (t, J = 1.8 Hz, 1H), 7.07−7.00
(m, 2H), 7.01−6.86 (m, 4H), 6.56 (dd, J = 8.5, 2.3 Hz, 1H), 6.48 (d, J =
2.3 Hz, 1H), 6.43 (d, J = 2.7 Hz, 1H), 5.61−5.43 (m, 2H), 4.61 (hept, J =
6.1 Hz, 1H), 3.85 (s, 3H), 3.78 (d, J = 18.0 Hz, 1H), 3.63 (d, J = 18.1 Hz,
1H), 3.40 (dt, J = 13.6, 4.8 Hz, 1H), 3.27−3.13 (m, 1H), 3.08−2.94 (m,
2H), 1.39 (d, J = 6.0 Hz, 3H), 1.33 (d, J = 6.0 Hz, 3H).13C NMR (101
MHz, CDCl3) δ 166.9, 163.1, 160.4, 157.0, 154.9, 139.9, 135.1, 133.3,
132.4, 131.0, 130.2, 129.3, 128.4, 128.0, 126.5, 122.0, 113.5, 104.6, 100.2,
72.0, 71.0, 69.3, 55.6, 50.0, 42.0, 40.5, 22.1 (2C). HRMS (ESI) exact
mass calcd for C30H31BrClN4O4 [M + H]+ 625.1217, found 625.1218.
tert-Butyl ((1R,2S)-2-Amino-2-(3-chlorophenyl)-1-(4-
chlorophenyl)ethyl)carbamate (S27). In a 100 mL flask was placed
β-Nitro Boc-amine 4ca (1.10 g, 2.67 mmol) in MeOH (25 mL), the
reaction mixture was stirred at room temperature, and then cobalt(II)
chloride (347 mg, 2.67 mmol) was added. The purple solution was
cooled to 0 °C, and sodium borohydride (1.51 g, 40.1 mmol) was added
in three portions over 45 min. Stirring was continued at 0 °C for 2 h, and
the reaction mixture was quenched with saturated aqueous NH4Cl and
adjusted to pH 10 with concentrated NH4OH. The aqueous layer was
extracted with ethyl acetate. The ethyl acetate layer was washed with
brine, dried (Na2SO4), filtered, and concentrated to give a white solid.
The crude product was purified on a silica gel column using a hexane/
22.1
ethyl acetate (0−45%) gradient (670 mg, 66%): [α]D = −11.9° (c
0.29, CH3OH); mp 162−163 °C; IR (film) 3361, 2983, 1682, 1525,
1492 cm−1; 1H NMR (400 MHz, CDCl3) δ 7.25−7.19 (m, 4H), 7.11 (s,
1H), 6.99−6.91 (m, 3H), 5.47 (s, 1H), 4.80 (s, 1H), 4.23 (s, 1H), 1.36
(s, 11H); 13C NMR (126 MHz, CDCl3) δ 155.0, 144.1, 136.8, 134.3,
133.4, 129.5, 128.7, 128.3, 127.7, 127.2, 125.1, 79.8, 59.4, 28.3; HRMS
(ESI) exact mass calcd for C19H23Cl2N2O2 [M + H]+ 381.1138, found
381.1131.
N-((1S,2R)-2-Amino-1-(3-chlorophenyl)-2-(4-chlorophenyl)-
ethyl)-4-chloro-2-isopropoxybenzamide (S28). To amine S27
(300 mg, 787 μmol) and 4-chloro-2-isopropoxybenzoic acid (169 mg,
787 μmol) in dichloromethane (4.0 mL) were added EDC·HCl
(196 mg, 1.02 mmol) and DMAP (9.61 mg, 79 μmol) at 0 °C, and the
reaction mixture was gradually warmed to room temperature. After
16 h the reaction mixture was diluted with water and extracted with
dichloromethane. The organic layers were combined, washed with
brine, dried (Na2SO4), filtered, and concentrated to give a white solid.
The crude product was triturated with dichloromethane and then
hexanes and dried under vacuum to give a white solid (420 mg, 92%),
which was used in the next step directly. To tert-butyl ((1R,2S)-2-(4-
chloro-2-isopropoxybenzamido)-2-(3-chlorophenyl)-1-(4-
chlorophenyl)ethyl)carbamate (370 mg, 640 μmol) in dichloromethane
(6 mL) was added TFA (1.98 mL, 25.7 mmol), and the reaction mixture
was stirred at room temperature for 16 h. The reaction mixture was
poured into aqueous NaHCO3 and extracted with dichloromethane.
The combined organic layers were washed with brine, dried (Na2SO4),
N-((1R,2S)-2-(3-Bromophenyl)-1-(4-chlorophenyl)-2-(2-iso-
propoxy-4-methoxybenzamido)ethyl)-3-oxopiperazine-1-car-
boxamide (S39). To amine S38 (190 mg, 367 μmol) in dichloro-
methane (2 mL) was added CDI (95 mg, 59 μmol) at room temperature
under N2. The reaction mixture was stirred for 1 h, piperazin-2-one
(77 mg, 0.771 mmol) was then added, and this mixture was warmed to
room temperature over 4 h. The solvent was removed, and the crude
product was purified by column chromatography (SiO2, 0−10% metha-
nol in dichloromethane) to give a white solid (137 mg, 58%): 1H NMR
(400 MHz, CDCl3) δ 8.39 (d, J = 8.0 Hz, 1H), 8.27 (d, J = 8.9 Hz, 1H),
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filtered, and concentrated. The residue was purified by column
chromatography (SiO2, methanol in dichloromethane 0−7%) to give
a white foam (290 mg, 95%): 1H NMR (400 MHz, CDCl3) δ 8.89 (d,
J = 8.2 Hz, 1H), 8.10 (d, J = 8.4 Hz, 1H), 7.28−7.18 (m, 4H), 7.17−7.11
(m, 2H), 7.05−6.96 (m, 4H), 6.84 (d, J = 7.7 Hz, 1H), 5.42 (dd, J = 8.2,
4.9 Hz, 1H), 4.79 (p, J = 6.0 Hz, 1H), 4.40 (d, J = 4.8 Hz, 1H), 1.53−1.40
(m, 8H); HRMS (ESI) exact mass calcd for C24H24Cl3N2O2 [M + H]+
477.0905, found 477.0897.
N-((1R,2S)-2-(4-Chloro-2-isopropoxybenzamido)-2-(3-chlor-
ophenyl)-1-(4-chlorophenyl)ethyl)-3-oxopiperazine-1-carbox-
amide (S29). To amine S28 (260 mg, 544 μmol) in dichloromethane
(3.0 mL) was added CDI (105 mg, 652 μmol) at 23 °C under a nitrogen
atmosphere; the reaction mixture was stirred for 1 h before piperazin-
2-one (109 mg, 1.088 mmol) was added, and the resulting mixture was
stirred for 15 h at room temperature. The solvent was removed, and the
crude product was purified by column chromatography (SiO2, 0−10%
methanol in dichloromethane) to give a white solid (250 mg, 76%): 1H
NMR (400 MHz, CDCl3) δ 8.39 (d, J = 7.9 Hz, 1H), 8.24 (d, J = 8.5 Hz,
1H), 7.57 (d, J = 5.3 Hz, 1H), 7.33−7.28 (m, 2H), 7.22−7.17 (m, 2H),
7.12−7.09 (m, 2H), 6.97−6.92 (m, 2H), 6.88 (d, J = 8.4 Hz, 2H), 6.45
(s, 1H), 5.77 (dd, J = 7.9, 2.5 Hz, 1H), 5.17 (dd, J = 5.2, 2.6 Hz, 1H),
4.75−4.64 (m, 1H), 4.14 (d, J = 1.2 Hz, 2H), 3.77−3.68 (m, 1H), 3.60
(dt, J = 13.3, 5.3 Hz, 1H), 3.42−3.37 (m, 2H), 1.26−1.17 (m, 6H);
HRMS (ESI) exact mass calcd for C29H30Cl3N4O4 [M + H]+ 603.1334,
found 603.1329.
cis-Imidazoline 28. To triphenylphosphine oxide (276 mg, 0.994
mmol) in dichloromethane (2 mL) was added trifluoromethanesulfonic
anhydride (0.084 mL, 0.497 mmol) at 0 °C, the reaction mixture
was stirred for 10 min, amide-urea S29 (150 mg, 0.248 mmol) in
dichloromethane (1.6 mL) was then added, and the reaction mixture
was stirred at 0 °C for 1 h and then warmed to room temperature before
the addition of saturated aqueous NaHCO3. The dichloromethane layer
was separated, and the aqueous layer was extracted with dichloro-
methane. The combined organic layers were washed with brine, dried
(Na2SO4), filtered, and concentrated. The crude product was purified by
column chromatography (SiO2, 0−7% methanol in dichloromethane)
to give a white solid (125 mg, 86%): [α]D22 = −95.2° (c 0.5, CH3OH);
IR (film) 3226, 2980, 1678, 1595, 1490, 1409 cm−1; 1H NMR (400
MHz, CDCl3) δ 7.62 (d, J = 8.2 Hz, 1H), 7.03 (ddt, J = 8.3, 5.6, 3.4 Hz,
5H), 7.00−6.93 (m, 2H), 6.87 (t, J = 7.9 Hz, 3H), 6.82 (s, 1H), 5.65−
5.49 (m, 2H), 4.64 (p, J = 6.1 Hz, 1H), 3.81 (d, J = 17.9 Hz, 1H), 3.68 (d,
J = 17.9 Hz, 1H), 3.35 (dt, J = 12.9, 4.6 Hz, 1H), 3.28−3.14 (m, 1H),
3.10−2.93 (m, 2H), 1.40 (d, J = 6.0 Hz, 3H), 1.36 (d, J = 6.0 Hz, 3H);
13C NMR (101 MHz, CDCl3) δ 166.7, 160.0, 156.2, 154.7, 139.4, 137.8,
159.2, 157.0, 154.9, 138.9, 135.4, 132.9, 132.4, 128.8, 128.5, 127.8, 120.3,
113.8, 113.6, 112.9, 104.6, 100.1, 72.4, 71.0, 69.4, 55.5, 55.1, 49.4, 42.0,
40.34, 22.1, 22.0; HRMS (ESI) exact mass calcd for C31H34ClN4O5
[M + H]+ 577.2218, found 577.2221.
N-((1S,2R)-2-Amino-1-(3-bromophenyl)-2-(4-chlorophenyl)-
ethyl)-4-cyano-2-isopropoxybenzamide (S40). To amine S37
(221 mg, 519 μmol) and 4-cyano-2-isopropoxybenzoic acid (107 mg,
519 μmol) in dichloromethane (2.6 mL) were added EDC·HCl
(129 mg, 675 μmol) and DMAP (6.3 mg, 52 μmol) at 0 °C, and the
reaction mixture was gradually warmed to room temperature over 16 h. The
reaction mixture was diluted with water and extracted with dichloro-
methane. The combined organic layers were washed with brine, dried
(Na2SO4), filtered, and concentrated to give a white solid. The crude
product was triturated with dichloromethane and hexanes, filtered, and
dried under vacuum to give a white solid (500 mg, 98%), which was used
for the next step directly. To tert-butyl ((1R,2S)-2-(3-bromophenyl)-1-
(4- chlorophenyl)-2-(4-cyano-2-isopropoxybenzamido)ethyl)-
carbamate (225 mg, 367 μmol) in dichloromethane (4 mL) was
added TFA (1.13 mL, 14.7 mmol) at room temperature, and the
reaction mixture was stirred under N2 for 16 h. The reaction mixture was
poured into saturated aqueous NaHCO3 and extracted with dichloro-
methane. The organic layer was washed with brine, dried (Na2SO4),
filtered, and concentrated to afford an oil. This crude oil was purified by
column chromatography (SiO2, 0−10% methanol in dichloromethane)
to give a white solid (183 mg, 97%): 1H NMR (400 MHz, CDCl3) δ 8.96
(d, J = 8.0 Hz, 1H), 8.31−8.20 (m, 1H), 7.41−7.35 (m, 1H), 7.32 (dd,
J = 8.1, 1.5 Hz, 1H), 7.29−7.20 (m, 4H), 7.08 (td, J = 7.8, 1.2 Hz, 1H),
7.03−6.97 (m, 2H), 6.86 (d, J = 7.1 Hz, 1H), 5.56−5.28 (m, 1H), 4.84
(hept, J = 6.1 Hz, 1H), 4.39 (d, J = 4.9 Hz, 1H), 1.63−1.44 (m, 8H);
HRMS (ESI) exact mass calcd for C25H24BrClN3O2 [M + H]+ 512.0742,
found 512.0735.
N-((1R,2S)-2-(3-Bromophenyl)-1-(4-chlorophenyl)-2-(4-
cyano-2-isopropoxybenzamido)ethyl)-3-oxopiperazine-1-car-
boxamide (S41). To amine S40 (105 mg, 205 μmol) in dichloro-
methane (1.2 mL) was added CDI (49.8 mg, 307 μmol) at room
temperature, and the reaction mixture was stirred for 1 h. Piperazin-2-
one (41.0 mg, 409 μmol) was added, and stirring was continued for 4 h
at room temperature. The reaction mixture was concentrated and
purified by column chromatography (SiO2, 0−10% methanol in
1
dichloromethane) to give a white solid (97 mg, 74%): H NMR (400
MHz, CDCl3) δ 8.53−8.34 (m, 2H), 7.53−7.42 (m, 1H), 7.37 (dd, J =
8.1, 1.4 Hz, 1H), 7.30−7.15 (m, 5H), 7.15−7.06 (m, 2H), 6.94−6.87
(m, 2H), 6.44 (d, J = 3.2 Hz, 1H), 5.75 (dd, J = 8.1, 3.1 Hz, 1H), 5.20
(dd, J = 5.7, 3.0 Hz, 1H), 4.74 (hept, J = 6.0 Hz, 1H), 4.17−4.08 (m,
2H), 3.78−3.67 (m, 1H), 3.66−3.55 (m, 1H), 3.40 (td, J = 5.5, 4.8, 2.0
Hz, 2H), 1.29−1.23 (m, 6H); HRMS (ESI) exact mass calcd for
C30H30BrClN5O4 [M + H]+ 638.1171, found 638.1158.
134.7, 133.9, 133.5, 131.8, 129.1, 128.4, 128.2, 127.9, 127.4, 126.0, 120.7,
119.6, 113.4, 72.4, 71.6, 69.1, 49.5, 41.7, 40.3, 22.0 (2C); HRMS (ESI)
exact mass calcd for C29H28Cl3N4O3 [M + H]+ 585.1227, found
585.1226.
cis-Imidazoline 30. To triphenylphosphine oxide (139 mg,
0.501 mmol) in dichloromethane (1 mL) was added trifluorometha-
nesulfonic anhydride (0.042 mL, 0.250 mmol) at 0 °C, the reaction
mixture was stirred at 0 °C for 10 min, amide-urea S41 (80 mg,
0.125 mmol) in dichloromethane (1 mL) was then added, and the
reaction mixture was stirred at 0 °C for 1 h and then warmed to room
temperature before the addition of aqueous NaHCO3. The dichloro-
methane layer was separated, and the aqueous layer was extracted with
dichloromethane. The combined dichloromethane layers were washed
with brine, dried (Na2SO4), filtered, and concentrated. The crude
product was purified by column chromatography (SiO2, 0−7%
methanol in dichloromethane) to give a white solid (64 mg, 82%):
[α]D23.7 = −75.0° (c 0.22, CH3OH); IR (film) 3214, 2980, 2923, 2230,
1678, 1598, 1566, 1493, 1413 cm−1; 1H NMR (400 MHz, CDCl3) δ 7.82
(d, J = 7.8 Hz, 1H), 7.35 (dd, J = 7.9, 1.4 Hz, 1H), 7.25−7.17 (m, 2H),
7.12 (d, J = 1.9 Hz, 1H), 7.10−7.04 (m, 2H), 6.98 (t, J = 7.7 Hz, 1H),
6.95−6.84 (m, 3H), 6.46 (d, J = 3.0 Hz, 1H), 5.69−5.55 (m, 2H), 4.69
(hept, J = 6.1 Hz, 1H), 3.93−3.73 (m, 2H), 3.30 (t, J = 5.4 Hz, 2H),
3.20−3.08 (m, 1H), 3.02 (dtd, J = 12.0, 7.9, 6.7, 4.0 Hz, 1H), 1.42 (d, J =
6.0 Hz, 3H), 1.39 (d, J = 6.0 Hz, 3H); 13C NMR (101 MHz, CDCl3) δ
166.2, 160.0, 155.5, 154.7, 139.4, 134.3, 133.9, 131.7, 130.8, 130.4, 129.4,
128.4, 128.3, 126.3, 124.2, 122.2, 118.2, 115.8, 115.2, 73.0, 71.9, 69.0,
cis-Imidazoline 29. To triphenylphosphine oxide (673 mg,
2.420 mmol) in dichloromethane (5 mL) was added trifluorometha-
nesulfonic anhydride (0.204 mL, 1.210 mmol) at 0 °C, the reaction
mixture was stirred at 0 °C for 10 min, N-((1R,2S)-1-(4-chlorophenyl)-
2-(2-isopropoxy-4-methoxybenzamido)-2-(3-methoxyphenyl)ethyl)-3-
oxopiperazine-1-carboxamide (360 mg, 0.605 mmol) in dichloro-
methane (3 mL) was then added, and the reaction mixture was stirred
at 0 °C for 1 h and then warmed to room temperature before the addi-
tion of saturated aqueous NaHCO3. The dichloromethane layer was
separated, and the aqueous layer was extracted with dichloromethane.
The combined dichloromethane layers were washed with brine, dried
(Na2SO4), filtered, and concentrated. The crude product was purified by
column chromatography (SiO2, 0−7% methanol in dichloromethane)
to give a white solid (264 mg, 76%): [α]D22 = −134.1° (c 0.4, CH3OH);
IR (film) 3215, 2979, 2937, 2837, 1674,1607,1492,1431 cm−1; 1H NMR
(400 MHz, CDCl3) δ 7.67 (d, J = 8.5 Hz, 1H), 7.02 (dd, J = 15.7, 8.1 Hz,
3H), 6.89 (d, J = 8.5 Hz, 3H), 6.63 (dd, J = 8.1, 2.1 Hz, 2H), 6.55 (dd, J =
8.5, 2.2 Hz, 1H), 6.47 (d, J = 2.1 Hz, 1H), 6.45−6.40 (m, 1H), 5.54 (d,
J = 9.7 Hz, 1H), 5.46 (d, J = 9.6 Hz, 1H), 4.59 (p, J = 6.0 Hz, 1H), 3.83 (s,
3H), 3.79−3.57 (m, 5H), 3.35 (dd, J = 8.5, 5.0 Hz, 1H), 3.18 (dt, J =
12.8, 5.3 Hz, 1H), 2.96 (t, J = 7.0 Hz, 2H), 1.37 (d, J = 6.0 Hz, 3H), 1.32
(d, J = 6.0 Hz, 3H); 13C NMR (101 MHz, CDCl3) δ 167.2, 163.0, 160.1,
6936
dx.doi.org/10.1021/jo501003r | J. Org. Chem. 2014, 79, 6913−6938

The Journal of Organic Chemistry
Article
49.7, 41.4, 40.4, 29.7, 21.9; HRMS (ESI) exact mass calcd for
C30H28BrClN5O3 [M + H]+ 620.1064, found 620.1071.
3H); HRMS (ESI) exact mass calcd for C31H36ClN4O6 [M + H]+
595.2325, found 595.2313.
tert-Butyl ((1R,2S)-2-Amino-1-(4-chlorophenyl)-2-(3-
methoxyphenyl)ethyl)carbamate (S34). In a 100 mL flask was
placed β-nitro Boc-amine 4ia (1.00 g, 2.46 mmol) in MeOH (24 mL),
the reaction mixture was stirred at room temperature, and then
cobalt(II) chloride (319 mg, 2.46 mmol) was added. The purple
solution was cooled to 0 °C, and then sodium borohydride (1.40 g,
36.9 mmol) was added in three portions over 45 min. Stirring was
continued at 0 °C for 75 min, and then the reaction mixture was treated
with saturated aqueous NH4Cl and its pH adjusted to 10 with
concentrated NH4OH. The aqueous layer was extracted with ethyl
acetate, and the combined organic layers were washed with brine, dried
(Na2SO4), filtered, and concentrated. The crude product was purified by
column chromatography (SiO2, 0−45% ethyl acetate in hexanes) to
ASSOCIATED CONTENT
* Supporting Information
Figures giving analytical data for all new compounds. This
material is available free of charge via the Internet at http://pubs.
acs.org.
■
S
AUTHOR INFORMATION
Corresponding Authors
*E-mail for R.K.G.: kip.guy@stjude.org.
*E-mail for J.N.J.: jeffrey.n.johnston@vanderbilt.edu.
Notes
■
22.5
afford an oil (440 mg, 48%): [α]D = −6.7° (c 0.45, CH3OH); IR
(film) 3383, 2977, 2836, 1699, 1600, 1491, 1436, 1412 cm−1; 1H NMR
(400 MHz, CDCl3) δ 7.23−7.15 (m, 3H), 6.94 (d, J = 8.0 Hz, 2H), 6.79
(ddd, J = 8.2, 2.7, 1.0 Hz, 1H), 6.65 (d, J = 7.6 Hz, 1H), 6.59 (t, J = 2.0
Hz, 1H), 5.54 (s, 1H), 4.82 (s, 1H), 4.28−4.12 (m, 1H), 3.73 (s, 3H),
1.53−1.23 (m, 11H); 13C NMR (101 MHz, CDCl3) δ 159.6, 155.1,
143.5, 137.4, 133.1, 129.3, 128.8, 128.1, 119.2, 113.2, 112.3, 79.7, 59.7,
55.2, 28.3; HRMS (ESI) exact mass calcd for C20H26ClN2O3 [M + H]+
377.1634, found 377.1635.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We are grateful to Jeremy Mason for his contributions to the
early stage of this project. The work was supported by the
National Institutes of Health (NIH) Grant No. GM084333
(J.N.J.) and the National Science Foundation (CHE 1156922:
REU support for J.C.T. & J.M.). SJ work was supported by the
American Lebanese Syrian Associated Charities (ALSAC) and
St. Jude Children’s Research Hospital (SJCRH).
N - ( ( 1 S , 2 R ) - 2 - A m i n o - 2 - ( 4 - c h l o r o p h e n y l ) - 1 - ( 3 -
methoxyphenyl)ethyl)-2-isopropoxy-4-methoxybenzamide
(S35). To amine S34 (403 mg, 1.07 mmol) and 2-isopropoxy-4-
methoxybenzoic acid (225 mg, 1.07 mmol) in dichloromethane
(5.4 mL) were added EDC·HCl (266 mg, 1.39 mmol) and DMAP
(13.1 mg, 107 μmol) at 0 °C, and the reaction mixture was gradually
warmed to room temperature over 16 h. The reaction mixture was
diluted with water and extracted with dichloromethane. The organic
layers were combined, washed with brine, dried (Na2SO4), filtered, and
concentrated to give a white solid. The crude product was triturated with
dichloromethane and hexanes, filtered, and dried under vacuum to give a
white solid (580 mg, 95%), which was used for the next step directly. To
tert-butyl ((1R,2S)-1-(4-chlorophenyl)-2-(2-isopropoxy-4-methoxy-
benzamido)-2-(3-methoxyphenyl)ethyl)carbamate (560 mg, 0.984
mmol) in dichloromethane (9 mL) was added TFA (3.04 mL,
39.5 mmol), and the reaction mixture was stirred at room temperature
for 16 h. The reaction mixture was then poured into saturated aqueous
NaHCO3 and extracted with dichloromethane. The organic layers were
combined and washed with brine, dried (Na2SO4), filtered, and
concentrated. The residue was purified by column chromatography
(SiO2, 0−7% methanol in dichloromethane) to give a white foam (459
mg, 99%): 1H NMR (400 MHz, CDCl3) δ 8.84 (d, J = 8.3 Hz, 1H), 8.14
(d, J = 8.8 Hz, 1H), 7.23 (d, J = 8.3 Hz, 2H), 7.16 (t, J = 7.9 Hz, 1H), 7.07
(d, J = 8.4 Hz, 2H), 6.76 (dd, J = 8.2, 2.5 Hz, 1H), 6.70 (d, J = 7.7 Hz,
1H), 6.60 (s, 1H), 6.55 (dd, J = 8.8, 2.2 Hz, 1H), 6.48 (d, J = 2.2 Hz, 1H),
5.45 (dd, J = 8.3, 5.2 Hz, 1H), 4.74 (p, J = 6.1 Hz, 1H), 4.40 (d, J = 5.2
Hz, 1H), 3.82 (s, 3H), 3.68 (s, 3H), 1.64−1.36 (m, 8H); HRMS (ESI)
exact mass calcd for C26H30ClN2O4 [M + H]+ 469.1896, found
469.1902.
N-((1R,2S)-1-(4-Chlorophenyl)-2-(2-isopropoxy-4-methoxy-
benzamido)-2-(3-methoxyphenyl)ethyl)-3-oxopiperazine-1-
carboxamide (S36). To amine S35 (290 mg, 618 μmol) in
dichloromethane (3.0 mL) was added CDI (150 mg, 928 μmol) at
room temperature under N2. The reaction mixture was stirred for 1 h,
piperazin-2-one (124 mg, 1.24 mmol) was then added, and the reaction
mixture was stirred for 15 h at room temperature. The solvent was
removed, and the crude product was purified by column chromatog-
raphy (SiO2, 0−10% methanol in dichloromethane) to give a white solid
(360 mg, 98%): 1H NMR (400 MHz, CDCl3) δ 8.41 (d, J = 7.7 Hz, 1H),
8.28 (d, J = 8.8 Hz, 1H), 7.94 (d, J = 5.0 Hz, 1H), 7.18−7.13 (m, 2H),
7.10 (d, J = 1.1 Hz, 1H), 6.95−6.86 (m, 2H), 6.87−6.80 (m, 1H), 6.66−
6.58 (m, 2H), 6.55 (dd, J = 8.0, 1.5 Hz, 1H), 6.46 (d, J = 2.2 Hz, 1H),
6.27 (d, J = 3.2 Hz, 1H), 5.74 (dd, J = 7.7, 2.2 Hz, 1H), 5.14 (dd, J = 5.0,
2.3 Hz, 1H), 4.65 (hept, J = 6.1 Hz, 1H), 4.16 (d, J = 1.3 Hz, 2H), 3.86 (s,
3H), 3.81−3.70 (m, 4H), 3.60 (ddd, J = 13.4, 6.5, 4.4 Hz, 1H), 3.41 (tdd,
J = 9.3, 5.9, 3.6 Hz, 2H), 1.19 (d, J = 6.0 Hz, 3H), 1.15 (d, J = 6.1 Hz,
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