Synthetic application and structural elucidation of axially chiral dicarboxylic acid: Asymmetric mannich-type reaction with diazoacetate, (diazomethyl)phosphonate, and (diazomethyl)sulfone

Article abstract of DOI:10.1021/jo2005999

The past decade has witnessed the burgeoning research fields of chiral Bronsted acid catalysis. However, carboxylic acids, arguably the most general acids in organic chemistry, have rarely been used as chiral Bronsted acid catalysts. In this context, we d

Full text of DOI:10.1021/jo2005999

ARTICLE
pubs.acs.org/joc
Synthetic Application and Structural Elucidation of Axially Chiral
Dicarboxylic Acid: Asymmetric Mannich-type Reaction with
Diazoacetate, (Diazomethyl)phosphonate, and (Diazomethyl)sulfone
Takuya Hashimoto, Hidenori Kimura, Hiroki Nakatsu, and Keiji Maruoka*
Department of Chemistry, Graduate School of Science, Kyoto University, Sakyo, Kyoto 606-8502, Japan
S Supporting Information
b
ABSTRACT: The past decade has witnessed the burgeoning
research fields of chiral Brønsted acid catalysis. However,
carboxylic acids, arguably the most general acids in organic
chemistry, have rarely been used as chiral Brønsted acid
catalysts. In this context, we developed axially chiral dicarboxylic
acid and evaluated its catalytic activity in asymmetric Mannich-
type reaction of aromatic aldehyde-derived N-Boc imines and
tert-butyl diazoacetate. To demonstrate the remarkable general-
ity of this catalytic system, tert-butyl diazoacetate was replaced
with its phosphorus and sulfur analogues, (diazomethyl)
phosphonate and (diazomethyl)sulfone, by which synthetically valuable chiral β-amino phosphonates and β-amino sulfones could
be obtained with high enantioselectivities under identical reaction conditions. X-ray crystallographic analysis of axially chiral
dicarboxylic acid complexed with a pyridine derivative revealed its unique internal hydrogen bonding, a property that serves as a
basis for its distinctive acidity and chiral scaffold.
’ INTRODUCTION
imines and diazoacetate, which could be successfully extended to
other diazo compounds. Especially, tolyl (diazomethyl)sulfone
was found to be a new viable option, giving chiral β-amino sul-
fones with high enantioselectivities. Elucidation of the X-ray
structure of axially chiral dicarboxylic acid complexed with a pyri-
dine derivative was carried out to confirm the formation of an
internal hydrogen bond to give Brønsted acid-assisted Brønsted
acid. Furthermore, this X-ray crystallographic analysis revealed
the remarkably wide dihedral angle of the binaphthyl unit of this
axially chiral dicarboxylic acid compared to the corresponding
1,10-bi-2-naphthol (BINOL) derived monophosphoric acids,
offering a distinctive chiral environment for asymmetric
transformation.
In the wake of recent groundbreaking research revealing the
utility of hydrogen bonding in asymmetric catalysis,1 chiral
Brønsted acid catalysis has now become an indispensable tool
for environmentally benign access to a myriad of chiral building
blocks.2 Despite the possibility to employ various hydrogen-bond
donors having different pKa values depending on the reaction
systems, the relatively mild and very common Brønsted acids,
carboxylic acids, have rarely been examined. The only exception
published before we initiated our work was the use of mandelic
acid derivative 1 in an asymmetric nitroso aldol reaction reported
by Momiyama and Yamamoto in 20053 (Figure 1). In this
context, we introduced axially chiral dicarboxylic acids (R)-2,
having a binaphthyl backbone and two carboxylic acid moieties,
as a new entry of chiral Brønsted acid catalysts in 2007,4 and their
high catalytic efficiency has been successfully demonstrated in
several asymmetric transformations in the last couple of years.5ꢀ7
These molecules were originally designed in anticipation of the
internal hydrogen bonding among two carboxylic acid moieties,
which would be beneficial to acquire sufficient acidity for catalysis
and, more importantly, to fix the position of the hydrogen atom
of otherwise freely rotating carboxylic acid. Thus fixed carboxylic
acid is expected to act as an active hydrogen-bond donor.
Modification of 3,30-positions of a binaphthyl unit is convention-
ally applied as a general approach to efficiently impart the chiral
information of the axial chirality to a remote substrate.
’ RESULTS AND DISCUSSION
At the initial stage of the development of axially chiral
dicarboxylic acid, we were particularly keen to find out the reac-
tion system that clearly shows the importance of the unique
acidity of the catalyst. Toward this end, we became aware of
BINOL-derived chiral monophosphoric acid catalyzed asym-
metric Mannich-type reaction of tert-butyl diazoacetate, which
was reported by Terada and co-workers in 2005.8 As rather exotic
N-(4-dimethylaminobenzoyl) imines were utilized in their re-
port, we were interested in the outcome of the reaction using
more conventional N-tert-butoxycarbonyl (N-Boc) imines.9
We report herein the detailed study of this axially chiral
dicarboxylic acid-catalyzed Mannich-type reaction between N-Boc
Received: March 20, 2011
Published: June 16, 2011
r
2011 American Chemical Society
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Figure 1. Carboyxlic acid as a new entry to chiral Brønsted acids.
Scheme 1. Comparison of Acidity Profile in Mannich-type
Reaction of Benzaldehyde-Derived N-Boc Imine with tert-
Butyl Diazoacetate
Table 1. Screening of Axially Chiral Dicarboxylic Acidsa
entry
catalyst (mol %)
conditions (temp, h) yieldb (%) eec (%)
1
(R)-2a (10)
(R)-2b (10)
(R)-2c (10)
(R)-2d (10)
(R)-2d (5)
rt, 6
33
25
35
38
39
38
81
29
17
49
69
74
95
95
2
rt, 20
rt, 20
rt, 16
0, 15
0, 38
0, 20
Scheme 2. Preparation of Axially Chiral Dicaboxylic Acids
3
4
5
6
7d
(R)-2e (5)
(R)-2e (5) + MS 4 Å
a Reactions were performed with benzaldehyde N-Boc imine (0.10
mmol) and tert-butyl diazoacetate (0.12 mmol) in the presence of
(R)-2 in CH2Cl2 (1.0 mL). b Isolated yield. c Determined by chiral
HPLC analysis. d With MS 4 Å (100 mg).
in 41% yield after 40 h. The least acidic 2-naphthoic acid 3 was
completely unproductive, giving 7a only in 3% yield within the
same time frame.
As the acidityꢀreactivity relationship and advantage of using
dicarboxylic acid as catalyst became clear in this Mannich-type
reaction of N-Boc imines and diazoacetate, we stepped forward
to the elaboration of the catalyst structure to create highly
effective axially chiral dicarboxylic acid. According to the proce-
dure developed in this laboratory for synthesis of phase-transfer
catalysts,12 3,30-positions of dicarboxylic acid (R)-413 were
functionalized with aryl groups in anticipation of imparting
the chiral environment of the binaphthyl moiety to substrates.
(Trimethylsilyl)ethyl ester (R)-9 was used as a substrate for
ortho-magnesiation-bromination, taking its late-stage deprotec-
tion to the free carboxylic acid in mind, as normal alkyl esters
arylated at 3,30-positions were found not to be hydrolyzed even
under harsh acidic or basic conditions. From the intermediate
(R)-10, a variety of aryl groups could be incorporated into cata-
lysts by SuzukiꢀMiyaura coupling to give (R)-11.14 Subsequent
deprotection of the (trimethylsilyl)ethyl group by the treatment
with tetrabutylammonium fluoride provided a variety of axially
chiral dicarboxylic acids (R)-2 (Scheme 2).
In the initial experiment, three different Brønsted acids—2-
naphthoic acid 3, (rac)-1,10-binaphthyl-2,20-dicarboxylic acid
(rac)-4, and (rac)-BINOL-derived monophosphoric acid (rac)-
5—were compared in the reaction of tert-butyl diazoacetate 6
and benzaldehyde-derived N-Boc imine in CH2Cl2 at room
temperature (Scheme 1). As a result, it became apparent that
monophosphoric acid 5 exhibited quite high reactivity compared
to the other two carboxylic acids. However, in conjunction with
the desired Mannich-type adduct 7a, a considerable amount of
8,10 which is assumed to be generated via migration of the phenyl
group from the diazonium intermediate,11 was obtained. On the
other hand, use of (rac)-4 furnished 7a as an only isolable adduct
As shown in Table 1, screening of catalysts identified a catalyst
(R)-2e bearing a 4-(tert-butyl)-2,6-dimethylphenyl group as
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Table 2. Use of tert-Butyl Diazoacetatea
Table 3. Use of Dimethyl (Diazomethyl)phosphonatea
a Reactions were performed with aromatic aldehyde N-Boc imine (0.10
mmol) and dimethyl (diazomethyl)phosphonate 12 (0.15 mmol) in the
presence of (R)-2e (0.005 mmol) and MS 4 Å (100 mg) in CH2Cl2
(1.0 mL). b Isolated yield. cDetermined by chiral HPLC analysis.
Table 4. Use of Tolyl (Diazomethyl)sulfonea
a Reactions were performed with aromatic aldehyde N-Boc imine (0.10
mmol) and tert-butyl diazoacetate 6 (0.15 mmol) in the presence of (R)-
2e (0.005 mmol) and MS 4 Å (100 mg) in CH2Cl2 (1.0 mL). b Isolated
yield. c Determined by chiral HPLC analysis. d Performed at ꢀ20 °C.
3,30-substituents,15 with which Mannich-type adduct was obtained
with 95% enantiomeric excess (ee) by carrying out the reaction in
CH2Cl2 at 0 °C (entry 6). Addition of molecular sieves was found
to be advantageous to increase the yield of the reaction, as they
would scavenge adventitious water that caused hydrolysis of
N-Boc imine (entry 7).
With these optimal reaction conditions in hand, we investigated
the substrate scope of this Mannich-type reaction using various aro-
matic aldehyde-derived N-Boc imines as summarized in Table 2.
As for the substitution pattern on the aromatic ring of N-Boc
imines, use of 2-, 3-, and 4-tolualdehyde-derived N-Boc imines all
provided the Mannich-type adducts 7bꢀd with high enantios-
electivities, although 2-substitution led to the requirement of a
longer reaction time (entries 2ꢀ4). 2-Naphthaldehyde-derived
N-Boc imine could be utilized as well (entry 5). Among the
functionalities of a different electronic property (entries 6ꢀ10),
attachment of a strongly electron-withdrawing substituent like a
nitro group resulted in a considerable decrease of the yield (entry
8), presumably due to inefficient interaction of the less basic
nitrogen lone pair of the imine to axially chiral dicarboxylic acid.
In the case of reaction with 2-furaldehyde-derived imine, the
enantioselectivity decreased slightly, although the reactivity was
remarkably high (entry 11). Accordingly, the reaction tempera-
ture could be lowered to improve the selectivity to give 7k in 78%
yield with 87% ee (entry 12). These reaction conditions could be
a Reactions were performed with aromatic aldehyde N-Boc imine (0.10
mmol) and tolyl (diazomethyl)sulfone 14 (0.15 mmol) in the presence of
(R)-2e (0.005 mmol) and MS 4 Å (100 mg) in CH2Cl2 (1.0mL). b Isolated
yield. c Determined by chiral HPLC analysis. d Performed at ꢀ20 °C.
applied to 3-furaldehyde-derived imine, with which the product
was obtained in 77% yield with 94% ee (entry 13).
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The noteworthy advantage of this procedure is its extension to
other diazo compounds stabilized with an electron-withdrawing
group. Namely, by simply applying the reaction conditions
established as above, dimethyl (diazomethyl)phosphonate 12
could be utilized in place of tert-butyl diazoacetate to give chiral
β-amino phosphonates 13 with excellent levels of enantioselec-
tivity as summarized in Table 3.16,17 In general, the reaction was
slower compared to the reaction with diazoacetate, whereas the
enantioselectivities were consistently high irrespective of the
N-Boc imines employed (entries 1ꢀ6). Both 2- and 3-furalde-
hyde-derived N-Boc imines could be converted to R-diazo-β-
amino phosphonates 13g and 13h with greater than 90% ee
(entries 7 and 8).
To further extend the potential of this axially chiral dicar-
boxylic acid-catalyzed reaction, we then turned our attention to
the use of tolyl (diazomethyl)sulfone 14 to give chiral β-amino
sulfones,18,19 in consideration of the attractive biological activities
of the sulfonylated compounds20 as well as the synthetic im-
portance of sulfonyl groups acting as a key reactive functionality.21
As anticipated, the reaction of tolyl (diazomethyl)sulfone 14 with
benzaldehyde-derived N-Boc imine proceeded without difficulty,
giving the corresponding β-amino sulfone 15a in 70% yield with
92% ee (Table 4, entry 1). Due to the lower reactivity of
(diazomethyl)sulfone compared to diazoacetate, the reaction of
2-tolualdehyde-derived N-Boc imine was too sluggish to provide
the adduct (less than 10% yield). In other cases, this novel
transformation had a broad generality, giving chiral β-amino
sulfones with enantioselectivities ranging from 90% to 94% ee
(entries 2ꢀ8).
As a unique synthetic application of chiral R-diazo-β-amino
sulfone, we implemented oxidative cleavage of the diazo moiety
of 15c to the oxo group by ozonolysis (Scheme 3). Thus-formed
acylsulfone 16 acted as a chiral R-aminoacyl donor and could be
trapped with methanol in situ to give R-amino acid ester 17 in
good yield without deteriorating the enantioselectivity. By com-
parison of the optical rotation of 17 with the literature, the
absolute configuration of 15c was confirmed to be (R).22
X-ray Crystallographic Analysis. Our attention was then
moved to elucidation of the catalyst structure by X-ray crystal-
lographic analysis to prove the existence of the postulated
internal hydrogen bonding between two carboxylic acids and
get insight about the chiral environment into which N-Boc
imines fit while one prochiral face is exposed.23 To this end,
we succeeded in obtaining the crystal of the 1:1 complex of (R)-
2e and 4-pyrrolidinopyridine grown in dichloromethane and
hexane (Figure 2).24
The distance of two inward oxygen atoms belonging to each
carboxylic acid [O(3) O(2)] was determined to be remark-
3 3 3
ably short, 2.480(4) Å, and that of one outward oxygen and Lewis
basic nitrogen atom of 4-pyrrolidinopyridine [O(1) N(1)]
3 3 3
was 2.676(5) Å. In addition, one hydrogen atom derived from the
carboxylic acid was actually found between two carboxylic acids,
as located in difference Fourier maps and refined isotropically.
These facts clearly indicated the existence of an intra- and
intermolecular hydrogen bonds as anticipated in our catalyst
design.25 The bond order of the carboxylic acid acting as a
hydrogen-bond donor for internal hydrogen bonding was normal,
as the single-bond character localized on the inward C(25)ꢀ
O(3) bond. On the other hand, another carboxylic acid sharing
its hydrogen with 4-pyrrolidinopyridine was highly delocalized,
and the partial double-bond character resides on the outward
C(5)ꢀO(1) bond. As a whole, the hydrogen-bonding network of
this complex is described as the donation of hydrogen from one
carboxylic acid to another carboxylate anion, which is conjugated
Scheme 3. Application of r-Diazo-β-aminosulfone as Chiral
r-Aminoacyl Donor
with protonated pyridinium salt [CO2ꢀH (OꢀCdO)ꢀ
3 3 3
HꢀN+]. Importantly, this internal hydrogen bonding makes
3 3 3
Figure 2. ORTEP diagrams of the 1:1 complex of (R)-2e and 4-pyrrolidinopyridine: (a) front view, (b) top view, and (c) side view. Hydrogen atoms,
solvent, and disordered atoms are omitted for clarity. Selected bond lengths (in angstroms): C(5)ꢀO(1) = 1.251(5), C(5)ꢀO(2) = 1.273(5),
C(25)ꢀO(3) = 1.307(5), C(25)ꢀO(4) = 1.221(5), O(3) O(2) = 2.480(4), and O(1) N(1) = 2.676(5).
3 3 3
3 3 3
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(diazomethyl)phosphonate and tolyl (diazomethyl)sulfone, thus
materializing a rare catalytic system giving β-amino esters, β-amino
phosphonates, and β-amino sulfones under identical reaction
conditions. X-ray crystallographic analysis of the catalyst com-
plexed with a pyridine derivative confirmed the existence of
internal hydrogen bonding between two carboxylic acid moieties
and the wide dihedral angle of the binaphthyl unit, which are
considered to be crucial for acquisition of sufficient reactivity and
efficient chiral scaffold.
Figure 3. Comparison of dihedral angles between axially chiral
dicarboxylic acid and BINOL-derived monophosphoric acid.
’ EXPERIMENTAL SECTION
General Information. Infrared (IR) spectra were recorded on a
Fourier transform infrared (FT-IR) spectrometer. 1H NMR spectra
were measured at 400 MHz. Data were reported as follows: chemical
shifts in parts per million (ppm) from tetramethylsilane as an internal
standard, integration, multiplicity (s = singlet, d = doublet, t = triplet, q =
quartet, dd = doubleꢀdoublet, m = multiplet, br = broad), coupling
constants (in hertz), and assignment. 13C NMR spectra were measured
at 100 MHz with complete proton decoupling. Chemical shifts were
reported in ppm from the residual solvent as an internal standard. High-
resolution mass spectra (HRMS) were performed on an electrospray
ionization time-of-flight (ESI-TOF) mass spectrometer. Optical rota-
tions were measured on a digital polarimeter. The products were purified
by flash column chromatography on silica gel 60 (230ꢀ400 mesh).
Dichloromethane was purchased from Kanto Chemical Co. Inc. as
“dehydrated” and further purified by passing through neutral alumina
under a nitrogen atmosphere. Spectral data for compounds (R)-2aꢀ2e,
7aꢀ7i,7k,13aꢀ13e,and13g were reported in our preliminary report.4 Diazo
compounds are potentially explosive and should be handled with care.28
General Procedure for Axially Chiral Dicarboxylic Acid-
Catalyzed Mannich-type Reaction of N-Boc Imines and
Diazo Compounds. The reaction flask containing powdered 4 Å
molecular sieves (100 mg) was flame-dried under vacuum. To the flask
were added (R)-2e (0.005 mmol, 3.3 mg), N-Boc imine (0.10 mmol),
and dichloromethane (1.0 mL), and the solution was cooled to the tem-
perature indicated in tables. Protection from light by aluminum foil was
necessary in the reaction with tolyl (diazomethyl)sulfone. To the mix-
ture was then added the corresponding diazo compound (0.15 mmol).
After completion of the reaction, the solution was directly submitted to
column chromatography on silica gel to give the corresponding product.
tert-Butyl (R)-3-(tert-Butoxycarbonylamino)-2-diazo-3-[3,4-(meth-
ylenedioxy)phenyl]propanoate (7j). Prepared according to the general
procedure with (3,4-methylenedioxy)benzaldehyde N-Boc imine (0.10
mmol, 24.9 mg) and tert-butyl diazoacetate (0.15 mmol, 21.3 mg). The
crude material was purified by column chromatography on silica gel
(eluted with hexane/diethyl ether = 5:1) to give the title compound as a
yellow amorphous solid [87% yield (34.1 mg), 92% ee]. Enantiomeric
purity was determined by HPLC analysis [Daicel Chiralcel OD-H,
hexane/2-propanol = 50:1, flow rate = 0.5 mL/min, retention time
16.1 min (minor) and 18.3 min (major)]. 1H NMR (400 MHz, CDCl3)
δ 6.83ꢀ6.76 (3H, m), 5.95 (2H, s), 5.52 (1H, d, J = 7.3 Hz), 5.30 (1H,
br s), 1.451 (9H, s), 1.449 (9H, s); 13C NMR (100 MHz, CDCl3) δ
165.2, 154.8, 148.1, 147.2, 133.3, 108.3, 106.8, 101.2, 82.0, 80.2, 61.1,
51.1, 28.34, 28.29; IR (neat) 3358, 2978, 2091, 1690, 1489, 1368, 1246,
1163, 1040 cmꢀ1; HRMS (ESI) exact mass calcd for C19H25N3O6 m/z
Figure 4. Plausible transition-state model of axially chiral dicarboxylic
acid-catalyzed Mannich-type reaction of diazo compounds.
a large nine-membered ring in the catalyst, leading to significant
broadening of the dihedral angle of the binaphthyl moiety to
93.4° [torsionangleofC(11)ꢀC(16)ꢀC(4)ꢀC(18)] (Figure 3).
This is in sharp contrast with BINOL-derived chiral monopho-
sphoric acids having a rigid seven-membered ring with reported
dihedral angles of around 55°,26 thus underlining the distinctive
chiral environment established by our axially chiral dicarboxylic
acid.
From these observations, we delineated a plausible transition-
state model of this Mannich-type reaction (Figure 4). N-Boc
imines would coordinate to axially chiral dicarboxylic acid as
4-pyrrolidinopyridine did in crystal to give a reactive complex,
while the steric bulk of 3,30-aryl groups and the binaphthyl unit
would harness the position of N-Boc imine by sterically prevent-
ing the formation of conformational isomers arising from the
rotation of O HꢀN hydrogen bond. Given the well-estab-
3 3 3
lished fact in chiral phosphoric acid catalysis that phosphoric acid
acts as a Brønsted acid/Lewis base bifunctional catalyst to acti-
vate electrophile and nucleophile simultaneously,27 it is envi-
saged that nucleophilic diazo compound approaches from the
side of the inward oxygen acting as a Lewis base while forming a
hydrogen bond with the R-hydrogen of diazoacetate.
’ CONCLUSIONS
414.1636 ([M + Na]+), found m/z 414.1635 ([M + Na]+); [R]2D7
+22.1 (c = 1.0, CHCl3, 92% ee).
=
In summary, we have developed axially chiral dicarboxylic acid
as a new entry to chiral Brønsted acid catalysts and succeeded in
evaluating its high catalytic performance and elucidating its
unique structure. Highly enantioselective Mannich-type reaction
between N-Boc imines and diazoacetate could be realized by
use of axially chiral dicarboxylic acid having 4-(tert-butyl)-2,6-
dimethylphenyl groups as 3,30-substituents. As a notable fea-
ture of this catalysis, we extended this procedure to dimethyl
tert-Butyl (R)-3-(tert-Butoxycarbonylamino)-2-diazo-3-(3-furyl)-
propanoate (7l). Prepared according to the general procedure with
3-furaldehyde N-Boc imine (0.10 mmol, 19.5 mg) and tert-butyl
diazoacetate (0.15 mmol, 21.3 mg). The crude material was purified
by column chromatography on silica gel (eluted with hexane/diethyl
ether = 5:1) to give the title compound as a yellow oil [77% yield
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ARTICLE
(26.0 mg), 94% ee]. Enantiomeric purity was determined by HPLC
analysis [Daicel Chiralpak AD-H, hexane/2-propanol = 50:1, flow rate =
0.5 mL/min, retention time 33.4 min (major) and 38.0 min (minor)].
1H NMR (400 MHz, CDCl3) δ 7.39 (2H, m), 6.37 (1H, m), 5.51 (1H, d,
J = 8.0 Hz), 5.29 (1H, br s), 1.47 (9H, s), 1.46 (9H, s); 13C NMR (100
MHz, CDCl3) δ 165.1, 154.8, 143.7, 139.6, 124.7, 109.1, 81.9, 80.3, 60.7,
44.7, 28.34, 28.29; IR (neat) 3350, 2978, 2093, 1690, 1506, 1368, 1252,
1163 cmꢀ1; HRMS (ESI) exact mass calcd for C16H23N3O5 m/z
N-Boc imine (0.10 mmol, 21.9 mg) and tolyl (diazomethyl)sulfone (0.15
mmol, 29.4 mg). The crude material was purified by column chromatog-
raphy on silica gel (eluted with toluene/EtOAc = 60:1) to give the title
compound [60% (25.1 mg), 90% ee]. Enantiomeric purity was deter-
mined by HPLC analysis [Daicel Chiralpak AD-H, hexane/2-propanol =
10:1, flow rate = 0.5 mL/min, retention time 35.0 min (minor), 40.0 min
(major)]. 1H NMR (400 MHz, CDCl3) δ 7.55 (2H, d, J = 8.4 Hz), 7.23
(2H, d, J = 8.4 Hz), 7.16 (1H, dd, J = 8.0, 7.6 Hz), 7.04 (1H, d, J = 7.6 Hz),
6.98 (1H, d, J= 8.0Hz), 6.90(1H, s), 5.70 (1H, d, J =8.0Hz), 5.30 (1H, br
s), 2.42 (3H, s), 2.23 (3H, s), 1.41 (9H, s); 13C NMR (100 MHz, CDCl3)
δ 154.5, 144.1, 140.0, 138.6, 136.8, 129.7, 128.9, 128.8, 126.9, 126.8, 123.2,
80.5, 70.9, 52.0, 28.2, 21.6, 21.3; IR (neat) 2085, 1710, 1495, 1367, 1327,
1244, 1147, 1088 cmꢀ1; HRMS (ESI) exact mass calcd for C21H25N3O4S
360.1530 ([M + Na]+), found m/z 360.1533 ([M + Na]+); [R]2D8
+23.7 (c = 1.0, CHCl3, 94% ee).
=
Dimethyl (R)-2-(tert-Butoxycarbonylamino)-1-diazo-2-[3,4-(meth-
ylenedioxy)phenyl]ethylphosphonate (13f). Prepared according to the
general procedure with (3,4-methylenedioxy)benzaldehyde N-Boc
imine (0.10 mmol, 24.9 mg) and dimethyl (diazomethyl)phosphonate
(0.15 mmol, 22.5 mg). The crude material was purified by column
chromatography on silica gel (eluted with hexane/ethyl acetate = 1:1) to
give the title compound as a yellow oil [64% yield (25.7 mg), 91% ee].
Enantiomeric purity was determined by HPLC analysis [Daicel Chiralcel
OD-H, hexane/2-propanol = 10:1, flow rate = 0.5 mL/min, retention
m/z 438.1458 ([M + Na]+), found m/z 438.1461 ([M + Na]+); [R]2D9
+19.0 (c = 1.0, CHCl3, 90% ee).
=
Tolyl (R)-2-(tert-Butoxycarbonylamino)-1-diazo-2-(4-tolyl)ethylsulfone
(15c). Prepared according to the general procedure with 4-tolualdehyde
N-Boc imine (0.10 mmol, 21.9 mg) and tolyl (diazomethyl)sulfone
(0.15 mmol, 29.4 mg). The crude material was purified by column
chromatography on silica gel (eluted with toluene/EtOAc = 60:1) to
give the title compound [61% (25.4 mg), 94% ee]. Enantiomeric purity
was determined by HPLC analysis [Daicel Chiralpak AD-H, hexane/
2-propanol = 10:1, flow rate = 0.5 mL/min, retention time 34.1 min
(minor), 40.9 min (major)]. 1H NMR (400 MHz, CDCl3) δ 7.59 (2H,
d, J = 8.0 Hz), 7.24 (2H, d, J = 8.0 Hz), 7.07ꢀ7.03 (4H, m), 5.69 (1H, d,
1
time 16.8 min (minor) and 20.0 min (major)]. H NMR (400 MHz,
CDCl3) δ 6.86ꢀ6.78 (3H, m), 5.97 (2H, s), 5.37 (2H, br s), 3.76 [3H, d,
2J(1H, 31P) = 11.8 Hz], 3.68 [3H, d, 2J(1H, 31P) = 11.8 Hz], 1.45 (9H, s);
13C NMR (100 MHz, CDCl3) δ 154.6, 148.1, 147.4, 133.0 [d, 3J(13C,
31P) = 3.3 Hz], 119.6, 108.4, 106.9, 101.3, 80.3, 53.1 [d, 2J(13C, 31P) =
5.7 Hz], 51.8, 46.0 [d, 1J(13C, 31P) = 229.4 Hz], 28.2; IR (neat) 3287,
2980, 2091, 1709, 1489, 1244, 1167, 1024 cmꢀ1; HRMS (ESI) exact
mass calcd for C16H22N3O7P m/z 422.1088 ([M + Na]+), found m/z
422.1092 ([M + Na]+); [R]D26 = +55.7 (c = 1.0, CHCl3, 91% ee).
Dimethyl (R)-2-(tert-Butoxycarbonylamino)-1-diazo-2-(3-furyl)-
ethylphosphonate (13h). Prepared according to the general procedure
with 3-furaldehyde N-Boc imine (0.10 mmol, 19.5 mg) and dimethyl
(diazomethyl)phosphonate (0.15 mmol, 22.5 mg). The crude material
was purified by column chromatography on silica gel (eluted with
hexane/ethyl acetate = 1:1) to give the title compound as a yellow oil
[78% yield (27.1 mg), 91% ee]. Enantiomeric purity was determined by
HPLC analysis [Daicel Chiralcel OJ-H, hexane/2-propanol = 20:1, flow
rate = 0.5 mL/min, retention time 24.8 min (minor) and 30.7 min
(major)]. 1H NMR (400 MHz, CDCl3) δ 7.45ꢀ7.41 (2H, m), 6.41 (1H,
s), 5.40 (1H, m), 5.31 (1H, br s), 3.77 [3H, d, 2J(1H, 31P) = 11.8 Hz],
3.73 [3H, d, 2J(1H, 31P) = 11.6 Hz], 1.46 (9H, s); 13C NMR (100 MHz,
CDCl3) δ 154.7, 143.9, 139.8, 124.4 [d, 3J(13C, 31P) = 3.3 Hz], 109.0,
80.3, 53.1 [d, 2J(13C, 31P) = 5.7 Hz], 53.0 [d, 2J(13C, 31P) = 4.9 Hz], 45.5,
J = 8.0 Hz), 5.29 (1H, br s), 2.42 (3H, s), 2.30 (3H, s), 1.40 (9H, s); 13
C
NMR (100 MHz, CDCl3) δ 154.5, 144.1, 139.9, 138.0, 134.0, 129.7,
129.5, 126.8, 126.0, 80.4, 70.9, 51.8, 28.2, 21.6, 21.0; IR (neat) 2085,
1711, 1510, 1327, 1165, 1149, 1087 cmꢀ1; HRMS (ESI) exact mass
calcd for C21H25N3O4S m/z 438.1458 ([M + Na]+), found m/z
438.1462 ([M + Na]+); [R]D28 = +28.9 (c = 1.0, CHCl3, 94% ee).
Tolyl (R)-2-(tert-Butoxycarbonylamino)-1-diazo-2-(2-naphthyl)ethyl-
sulfone (15d). Prepared according to the general procedure with
2-naphthaldehyde N-Boc imine (0.10 mmol, 25.5 mg) and tolyl
(diazomethyl)sulfone (0.15 mmol, 29.4 mg). The crude material was
purified by column chromatography on silica gel (eluted with toluene/
EtOAc = 50:1) to give the title compound [77% (34.6 mg), 93% ee].
Enantiomeric purity was determined by HPLC analysis [Daicel Chir-
alpak AD-H, hexane/2-propanol = 10:1, flow rate = 1.0 mL/min,
1
retention time 20.0 min (minor), 24.7 min (major)]. H NMR (400
MHz, CDCl3) δ 7.76 (1H, m), 7.72ꢀ7.68 (2H, m), 7.61 (1H, s), 7.52ꢀ
7.44 (4H, m), 7.18 (1H, dd, J = 8.8, 1.6 Hz), 7.06 (2H, d, J = 8.0 Hz), 5.91
(1H, d, J = 6.8 Hz), 5.54 (1H, br s), 2.32 (3H, s), 1.43 (9H, s); 13C NMR
(100 MHz, CDCl3) δ 154.6, 144.1, 139.8, 134.1, 133.0, 132.9, 129.6,
128.8, 128.0, 127.5, 126.7, 126.44, 126.42, 125.2, 123.9, 80.6, 70.8, 52.2,
28.2, 21.4; IR (neat) 2360, 2340, 2083, 1710, 1495, 1368, 1323, 1306,
1244, 1146 cmꢀ1; HRMS (ESI) exact mass calcd for C24H25N3O4S m/z
1
45.4 [d, J(13C, 31P) = 230.2 Hz], 28.2; IR (neat) 3273, 2978, 2091,
1709, 1524, 1524, 1248, 1165, 1024 cmꢀ1; HRMS (ESI) exact mass
calcd for C13H20N3O6P m/z 368.0982 ([M + Na]+), found m/z
368.0983 ([M + Na]+); [R]D23 = +67.1 (c = 1.0, CHCl3, 91% ee).
Tolyl (R)-2-(tert-Butoxycarbonylamino)-1-diazo-2-phenylethylsulfone
(15a). Prepared according to the general procedure with benzaldehyde
N-Boc imine (0.10 mmol, 20.5 mg) and tolyl (diazomethyl)sulfone
(0.15 mmol, 29.4 mg). The crude material was purified by column
chromatography on silica gel (eluted with toluene/EtOAc = 60:1) to
give the title compound [70% (28.1 mg), 92% ee]. Enantiomeric purity
was determined by HPLC analysis [Daicel Chiralpak AD-H, hexane/
2-propanol = 10:1, flow rate = 0.5 mL/min, retention time 43.1 min
(minor), 48.6 min (major)]. 1H NMR (400 MHz, CDCl3) δ 7.57 (2H,
d, J = 8.4 Hz), 7.29ꢀ7.21 (5H, m), 7.18 (2H, m), 5.73 (1H, d, J = 6.8
Hz), 5.35 (1H, br s), 2.41 (3H, s), 1.40 (9H, s); 13C NMR (100 MHz,
CDCl3) δ 154.5, 144.2, 139.9, 136.9, 129.8, 128.8, 128.2, 126.8, 126.1,
80.5, 70.9, 51.9, 28.2, 21.5; IR (neat) 2085, 1711, 1597, 1495, 1452,
1367, 1325, 1238, 1145, 1088 cmꢀ1; HRMS (ESI) exact mass calcd for
C20H23N3O4S m/z 424.1301 ([M + Na]+), found m/z 424.1301 ([M +
Na]+); [R]D30 = +9.7 (c = 1.0, CHCl3, 92% ee).
474.1458 ([M + Na]+), found m/z 474.1463 ([M + Na]+); [R]3D1
+26.2 (c = 1.0, CHCl3, 93% ee).
=
Tolyl (R)-2-(tert-Butoxycarbonylamino)-1-diazo-2-(4-chlorophe-
nyl)ethylsulfone (15e). Prepared according to the general procedure
with 4-chlorobenzaldehyde N-Boc imine (0.10 mmol, 24.0 mg) and tolyl
(diazomethyl)sulfone (0.15 mmol, 29.4 mg). The crude material was
purified by column chromatography on silica gel (eluted with toluene/
EtOAc = 60:1) to give the title compound [60% (25.3 mg), 90% ee].
Enantiomeric purity was determined by HPLC analysis [Daicel Chir-
alpak AD-H, hexane/2-propanol = 10:1, flow rate = 0.5 mL/min, reten-
tion time 29.7 min (minor), 35.8 min (major)]. 1H NMR (400 MHz,
CDCl3) δ 7.53 (2H, d, J = 8.4 Hz), 7.27ꢀ7.15 (4H, m), 7.09 (2H, d, J =
8.4 Hz), 5.70 (1H, d, J = 8.0 Hz), 5.40 (1H, br s), 2.43 (3H, s), 1.41 (9H,
s); 13C NMR (100 MHz, CDCl3) δ 154.5, 144.4, 139.8, 135.5, 134.1,
129.8, 128.9, 127.6, 126.7, 80.7, 70.6, 51.7, 28.2, 21.6; IR (neat) 2360,
2340, 2085, 1710, 1595, 1490, 1454, 1393, 1367, 1325, 1242,
1147 cmꢀ1; HRMS (ESI) exact mass calcd for C20H22ClN3O4S m/z
Tolyl (R)-2-(tert-Butoxycarbonylamino)-1-diazo-2-(3-tolyl)ethylsulfone
(15b). Prepared according to the general procedure with 3-tolualdehyde
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dx.doi.org/10.1021/jo2005999 |J. Org. Chem. 2011, 76, 6030–6037

The Journal of Organic Chemistry
ARTICLE
458.0912 ([M + Na]+), found m/z 458.0919 ([M + Na]+); [R]3D0
+11.9 (c = 1.0, CHCl3, 90% ee).
=
hexane/ethanol = 200:1, flow rate = 0.5 mL/min, retention time 25.7
min (minor), 30.9 min (major)]. [R]2D9 = ꢀ122.2 (c = 1.0, CHCl3,
94% ee). Absolute configuration of the title compound was determined
by the comparison of its optical rotation with the same compound
reported in the literature.22
Tolyl (R)-2-(tert-Butoxycarbonylamino)-1-diazo-2-(4-methoxyphe-
nyl)ethylsulfone (15f). Prepared according to the general procedure
with 4-methoxybenzaldehyde N-Boc imine (0.10 mmol, 23.5 mg) and
tolyl (diazomethyl)sulfone (0.15 mmol, 29.4 mg). The crude material
was purified by column chromatography on silica gel (eluted with
toluene/EtOAc = 60:1) to give the title compound [71% (30.8 mg),
95% ee]. Enantiomeric purity was determined by HPLC analysis [Daicel
Chiralpak AD-H, hexane/2-propanol = 10:1, flow rate = 0.5 mL/min,
’ ASSOCIATED CONTENT
Supporting Information. 1H and 13C NMR for all
S
b
new compounds (PDF) and crystallographic information for
the complex of (R)-2e and 4-pyrrolidinopyridine (CIF). This
material is available free of charge via the Internet at http://
pubs.acs.org.
1
retention time 54.1 min (minor), 65.1 min (major)]. H NMR (400
MHz, CDCl3) δ 7.58 (2H, d, J = 8.4 Hz), 7.24 (2H, d, J = 8.4 Hz), 7.08
(2H, d, J = 8.8 Hz), 6.78 (2H, m), 5.67 (1H, d, J = 7.6 Hz), 5.28 (1H, br
s), 3.77 (3H, s), 2.42 (3H, s), 1.40 (9H, s); 13C NMR (100 MHz,
CDCl3) δ 159.4, 154.5, 144.1, 140.0, 129.8, 129.0, 127.4, 126.8, 114.2,
80.4, 71.0, 55.2, 51.5, 28.2, 21.6; IR (neat) 2083, 1710, 1610, 1510, 1325,
1247, 1145, 1085, 812 cmꢀ1; HRMS (ESI) exact mass calcd for
C21H25N3O5S m/z 454.1407 ([M + Na]+), found m/z 454.1411 ([M
+ Na]+); [R]D30 = +17.2 (c = 1.0, CHCl3, 95% ee).
’ AUTHOR INFORMATION
Corresponding Author
*E-mail maruoka@kuchem.kyoto-u.ac.jp.
Tolyl (R)-2-(tert-Butoxycarbonylamino)-1-diazo-2-[3,4-(methylenedi-
oxy)phenyl]ethylsulfone (15g). Prepared according to the general pro-
cedure with 3,4-(methylenedioxy)benzaldehyde N-Boc imine (0.10
mmol, 24.9 mg) and tolyl (diazomethyl)sulfone (0.15 mmol, 29.4 mg).
The crude material was purified by column chromatography on silica gel
(eluted with toluene/EtOAc = 50:1) to give the title compound [54%
(23.9 mg), 94% ee]. Enantiomeric purity was determined by HPLC
analysis [Daicel Chiralpak AD-H, hexane/2-propanol = 10:1, flow rate =
0.5 mL/min, retention time 62.7 min (minor), 92.2 min (major)]. 1H
NMR (400 MHz, CDCl3) δ 7.60 (2H, d, J = 8.4 Hz), 7.26 (2H, d, J = 8.4
Hz), 6.70ꢀ6.64 (2H, m), 6.59 (1H, d, J = 1.6 Hz), 5.92 (2H, m), 5.62
(1H, d, J = 8.0 Hz), 5.28 (1H, br s), 2.43 (3H, s), 1.41 (9H, s); 13C NMR
(100 MHz, CDCl3) δ 154.4, 148.1, 147.5, 144.2, 139.8, 130.9, 129.8,
126.8, 119.6, 108.3, 106.7, 101.3, 80.6, 70.9, 51.8, 28.2, 21.5; IR (neat)
2083, 1711, 1503, 1487, 1323, 1238, 1148 cmꢀ1; HRMS (ESI) exact
mass calcd for C21H23N3O6S m/z 468.1200 ([M + Na]+), found m/z
468.1182 ([M + Na]+); [R]D29 = +27.4 (c = 1.0, CHCl3, 94% ee).
Tolyl (R)-2-(tert-Butoxycarbonylamino)-1-diazo-2-(2-furyl)ethyl-
sulfone (15h). Prepared according to the general procedure with 2-fur-
aldehyde N-Boc imine (0.10 mmol, 19.5 mg) and tolyl (diazomethyl)-
sulfone (0.15 mmol, 29.4 mg). The crude material was purified by column
chromatography on silica gel (eluted with toluene/EtOAc = 60:1) to give
the title compound [80% (31.2 mg), 90% ee]. Enantiomeric purity was
determined by HPLC analysis [Daicel Chiralpak AD-H, hexane/2-propa-
nol = 10:1, flow rate = 0.5 mL/min, retention time 42.3 min (major),
51.1 min (minor)]. 1H NMR (400 MHz, CDCl3) δ 7.59 (2H, d, J = 8.4
Hz), 7.25 (2H, d, J = 8.4 Hz), 7.17 (1H, m), 6.28ꢀ6.24 (2H, m), 5.77 (1H,
d, J = 6.8 Hz), 5.44 (1H, br s), 2.41 (3H, s), 1.41 (9H, s); 13C NMR (100
MHz, CDCl3) δ 154.3, 149.5, 144.1, 142.6, 139.9, 129.7, 126.7, 110.4,
107.8, 80.7, 69.5, 47.1, 28.1, 21.5; IR (neat) 2085, 1714, 1597 1497, 1454,
1368, 1327, 1306, 1233, 1148 cmꢀ1; HRMS (ESI) exact mass calcd for
C18H21N3O5S m/z 414.1094 ([M + Na]+), found m/z 414.1096 ([M +
Na]+); [R]D30 = ꢀ20.2 (c = 1.0, CHCl3, 90% ee).
’ ACKNOWLEDGMENT
This work was partially supported by a Grant-in-Aid for
Scientific Research from the MEXT, Japan. T.H. acknowledges
a Grant-in-Aid for Young Scientists (B). We are grateful to
Tomohiro Sato for X-ray analysis.
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