Asymmetric synthesis of nonracemic primary amines via spiroborate-catalyzed reduction of pure (E)- and (Z)-O-benzyloximes: Applications toward the synthesis of calcimimetic agents

Article abstract of DOI:10.1021/jo400371x

Highly enantiopure (1-aryl)- and (1-naphthyl)-1-ethylamines were synthesized by the borane-mediated reduction of single-isomeric (E)- and (Z)-O-benzyloxime ethers using the stable spiroborate ester derived from (S)-diphenyl valinol and ethylene glycol as the chiral catalyst. Primary (R)-arylethylamines were prepared by the reduction of pure (Z)-ethanone oxime ethers in up to 99% ee using 15% of catalyst. Two convenient and facile approaches to the synthesis of new and known calcimimetic analogues employing enantiopure (1-naphthalen-1-yl)ethylamine as chiral precursor are described.

Full text of DOI:10.1021/jo400371x

Article
pubs.acs.org/joc
Asymmetric Synthesis of Nonracemic Primary Amines via
Spiroborate-Catalyzed Reduction of Pure (E)- and
(Z)‑O‑Benzyloximes: Applications toward the Synthesis of
Calcimimetic Agents
Wenhua Ou, Sandraliz Espinosa, Hector J. Melendez, Silvia M. Farre, Jaime L. Alvarez, Valerie Torres,
́
́
́
Ileanne Martínez, Kiara M. Santiago, and Margarita Ortiz-Marciales*
Department of Chemistry, University of Puerto RicoHumacao, Call Box 860, Humacao 00792, Puerto Rico
S
* Supporting Information
ABSTRACT: Highly enantiopure (1-aryl)- and (1-naphthyl)-1-ethylamines were synthesized by the borane-mediated reduction
of single-isomeric (E)- and (Z)-O-benzyloxime ethers using the stable spiroborate ester derived from (S)-diphenyl valinol and
ethylene glycol as the chiral catalyst. Primary (R)-arylethylamines were prepared by the reduction of pure (Z)-ethanone oxime
ethers in up to 99% ee using 15% of catalyst. Two convenient and facile approaches to the synthesis of new and known
calcimimetic analogues employing enantiopure (1-naphthalen-1-yl)ethylamine as chiral precursor are described.
Free ionized Ca2+ is an important messenger in a variety of
cellular functions, playing a key role in blood coagulation,
INTRODUCTION
■
Nonracemic amines are powerful pharmacophores due to their
spatial arrangement and inherent ability to form hydrogen
bonds. Consequently, research on the asymmetric synthesis of
neurotransmitter release, myocardial functions, and mainte-
nance of skeletal integrity.4a,b The main function of the
parathyroid gland is to maintain the Ca2+ extracellular level in
small amino intermediaries has become an important field in
the body by controlling the secretion of the parathyroid
pharmaceutical chemistry.1−6 It is well established that
hormone (PTH).4c−e,f However, when a medical condition is
enantiomers of chiral drugs often differ significantly in their
present, such as chronic kidney disease (CKD) and parathyroid
pharmacological, toxicological, pharmacodynamic and pharma-
carcinoma, this hormone is produced excessively leading to
cokinetic properties. Hence, new methods for the synthesis of
secondary hyperparathyroidism (sHPT). If not promptly
both enantiomers and careful evaluation of new enantiopure
treated, sHPT can cause bone malformation, tissue calcification,
and fractures as well as other disorders. Up to now, the
treatment of sHPT has been accomplished by controlling the
drugs is of great importance.2 Chiral primary amines containing
an asymmetric α-benzylic carbon are widely used as key
precursors in the synthesis of a broad variety of enantiopure
drugs.2−6 Relevant examples of chiral amino drugs illustrating
the most bioactive enantiomer are shown in Figure 1. The (S)-
α-arylalkyl amino fragments are commonly present in a variety
of neuroactive drugs such as in rivastigmine (Exelon Novartis),
a well-known anticholinesterase agent used for the treatment of
Alzheimer disease.2a,3c,d Additionally, the active (S) amino
enantiomer is found in the antidepressant sertraline (Zoloft
Pfizer)3a and in repaniglide (Prandin Novo Nordisk), a new
drug used for the treatment of type II diabetes.3b On the other
hand, the more active (R) isomer is found in vanilloid 1
(TRPV1), AMG 628 candidate,3e a transient receptor potential
antagonist used for the treatment of chronic pain, as well as in
the novel calcimimetic drug, cinacalcet (Sensipar Amgen).4,5
The (R) enantiomer of cinacalcet is 100 times more active than
is its (S) isomer.4c
calcium levels through diet and vitamin D supplements. Surgery
is the frequent treatment for patients with parathyroid
carcinoma. The recent most effective treatment for the control
of PTH has been the use of new drugs known as calcimimetic
agents.4i,j These are novel compounds which mimic the effects
of extracellular Ca2+ at the calcium-sensing receptor (CaSR),
thereby effectively suppressing the PTH levels with a resultant
decrease in blood Ca2+ concentrations. In 2004, cinacalcet-HCl
(Figure 1) was the first calcimimetic agent approved by the
FDA for the treatment of sHPT. It is presently the only drug in
the market.4j Other candidates such as calindol,5a calhex 231,5b
NPS R-4675c,d and Amgen pyrazole5e (Figure 2) with potent
and selective activity on the parathyroid calcium receptor are
Received: March 4, 2013
© XXXX American Chemical Society
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Figure 1. Most active single isomeric drugs.
Figure 2. Calcium receptor agonists candidates.
Scheme 1. Synthesis of Calcimimetic Analogues Using Enantiopure Amines
under pharmacokinetic studies. Although clinical studies
demonstrated that NPS R-568 effectively lowered the blood
level of PTH, its clinical development was discontinued because
of its low bioavailability and poor metabolism.4c,d,i The
synthesis and biological studies of new and more effective
calcimimetic agents is presently an area of great relevance.5e−i
In addition, enantiomerically pure primary arylalkyl amines
are also widely used as chiral auxiliaries and ligands in catalytic
and stoichiometric asymmetric synthesis, as well as chirality
transfer reagents and resolving agent.1,6 Hence, the develop-
ment of new and convenient methods for the synthesis of these
enantioenriched amino compounds continues to be an area of
great importance in organic chemistry.1,2 Although there are a
variety of chemical and enzymatic processes for the preparation
of nonracemic primary amines,1,2,5,6 the asymmetric reduction
of oxime ethers has been a preferred approach due to the
availability of suitable methods to prepare pure (E)-oximes.7a−c
Since the first study by Itsuno and co-workers in 1987, the
reduction of acetophenone O-substituted oximes by borane in
the presence of chiral borane reagents, particularly oxazabor-
olidines, has been broadly studied to obtain nonracemic
primary phenylalkylamines.7 However, greater than stoichio-
metric amounts of these expensive chiral boron reagents were
required to achieve high enantioselectivity.7h The first effective
catalytic method for the borane-mediated reduction of (E)-
benzyloxime ethers was successfully developed in our
laboratory using the stable spiroaminoborate ester (1) derived
from (S)-diphenylvalinol and ethylene glycol (EG-DPV), as a
catalytic agent. Enantiopure primary amines were obtained in
high yield using low catalytic loading, usually less than 10% of
the catalyst.8a,b This method was effectively applied to the
asymmetric synthesis of a range of heteroaryl and heterocyclic
amines8c and to nicotinic analogues8d,e with excellent
enantioselectivity. The biological importance of nonracemic
(S)- and (R)-arylethylamines, particularly those containing
halogen- and alkoxy-substituted aromatic rings, prompted us to
study the synthesis and reduction of isomerically pure (E)- and
(Z)-benzyloxime ethers. The product amines were investigated
in their conversion to both known and new calcimimetic
analogues, as is illustrated in Scheme 1. Moreover, we felt that
the development of an effective catalytic asymmetric synthesis
of enantiopure primary α-alkylbenzylic amines and naphthalen-
B
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Table 1. Synthesis and Reduction of (E)-1-Aryl and 1-Naphthylethanone (O)-Benzyloximes
a
b
c
Isolated yield of pure E isomer. Isolated yield of pure (E)-benzyloxime isolated by column chromatography on silica gel. Enantiopurity
d
determined by GC of acetyl derivatives on chiral column (CP-Chirasil-Dex-CB). Crude product.
1-yl-alkylamines through a facile and environmentally friendly
method would offer enormous promise for developing efficient
new routes to a wide diversity of pharmaceutical products.
such as rivastigmine, the synthesis of representative enantiopure
amines was of interest.8 (E)-Aryl benzyl oximes were prepared
from the corresponding ketone using hydroxylamine and
sodium carbonate at 65 °C at a weakly acidic pH. As indicated
in Table 1, the (E)-oximes were obtained in moderate to high
yields after recrystallization. Subsequently, the oximes were
converted to their benzyloxime ethers using NaH and benzyl
bromide in DMF at −30 °C. The pure (E)-O-benzyloximes
were obtained in modest to good yields after careful
purification by column chromatography or preparative TLC.
RESULTS AND DISCUSSION
■
Asymmetric Synthesis of Nonracemic (S)-Primary
Amines. Initially, because of the biological importance of
(S)-arylethylamines containing F, Cl, Br, CF3, methoxy and
thiomethyl substituents as precursors for the synthesis to a wide
variety of chiral drugs, in particular neuroactive compounds,
C
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Scheme 2. Synthesis of (Z)-(O)-Benzyloxime Ethers
Table 2. Asymmetric Reduction of Representative (Z)-Benzyloximes
a
b
c
Isolated yield. Reduction conditions: 0.15 equiv of spiroborate catalyst 1, BH3−THF, THF, 0 °C. Isolated yield of acetamide derivatives.
d
Determined by GC of acetyl derivatives on chiral column (CP-Chirasil-Dex CB).
1
These were characterized by H and 13C NMR analysis and
confirmed by GC−MS. Similarly, the (E)-1-(naphthlen-1-
yl)ethanone oxime and its corresponding O-benzyloxime were
prepared in high isomeric purity and in good yields (Table 1).
The asymmetric reduction of the previously prepared (E)-O-
benzyl oximes in dioxane was conducted with 10% spiroborate
ester 1 (EG-DPV) and 4 equiv of BH3−THF at 0 °C for 3
days.8 The desired pure (S) amines were isolated as their N-
acetyl derivatives by the reaction of the crude product with
acetic anhydride, triethylamine and DMAP in methylene
chloride. The ee’s of the acetylated derivatives were determined
by GC analysis using CP-Chirasil-Dex-CB as the stationary
phase. As is illustrated in Table 1, the primary amines, isolated
as their acetyl derivatives, were obtained in good to excellent
yields and excellent enantiopurity (up to 98% ee) after column
chromatography or preparative TLC. Interestingly, no sig-
nificant substituent effects for either electron-donating or
electron-withdrawing groups on the aromatic rings were
observed in the enantioselective reduction of the (E)-
benzyloxime ethers. The enantiomeric purities of the amine
depended more on the isomeric purity of the benzyloxime ether
precursor.
Asymmetric Synthesis of (R) Primary Amines. Contrary
to the reduction of (E)-benzyloxime ethers with boranes in the
D
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Scheme 3. Synthesis of Class I Calcimimetic Analogues
presence of chiral catalysts, the enantioselective reduction of
(Z)-oxime ethers has rarely been examined, possibly because of
the difficulty in efficiently obtaining the (Z)-oxime ethers in
pure form.6b,9 Consequently, limited information is available on
the effect of (E)/(Z) isomerism on the asymmetric reduction of
the imine. The stereoselectivity for both the E and Z isomers in
the reduction, using the spiroborate−borane system, was
therefore of interest. Although the (R)-amines can be prepared
by the reduction of (E)-benzyloxime, using the spiroborate
derived from (S)-diphenylvalinol as a chiral source, the high
cost of this amino alcohol derived from an unnatural amino
acid makes this route less attractive. Accordingly, we decided to
investigate the reduction of (Z)-benzyloximes using the
spiroborate 1 catalyst to obtain the desired (R)-amines.
benzyloximes. Unexpectedly, the enantioselectivity was higher
in THF than in dioxane at 0 °C.
Under the previous established method (0.15 equiv of
spiroborate catalyst 1, BH3−THF, THF, 0 °C), the (Z)-
arylethyl- and (Z)-1-naphthylethyl-(O)-benzyl oximes shown in
Table 2 were efficiently reduced obtaining the desired primary
amines. Representative (R)-(1-aryl)- and 1-(naphthalen-1-
yl)ethylamines were converted to their acetamide derivatives
in good yield and high enantiomeric purity (up to 99% ee), for
all but the 4-nitro substituted phenyl ethylamine (80% ee).
Synthesis of Calcimimetic Analogues. As mentioned
above, calcimimetic agents are small organic molecules that
mimic the effects of extracellular Ca2+ at the calcium sensing
receptor (CaSR). These drugs are called type II calcimimetics
since they decrease the plasma levels of Ca2+ and PTH acting as
allosteric agonists by binding at sites distinct from the
extracellular Ca2+. Cinacalcet, shown in Figure 1, has become
the only approved treatment,4 with only limited numbers of
calcimimetic analogues presently under study.5 Because of the
urgency in the growth of new drugs for the treatment of HPT,
we were interested in developing efficient methods for the
synthesis of both known and new calcimimetic agents. In
general, the structure of calcimimetic compounds contains,
mainly, two sections: the (R)-aryl- or (R)-naphthylalkyl amino
group plus an aryl group connected through an aliphatic chain
(Figure 2). Since the binding of calcimimetic agents to the CaR
depends on electrostatic interactions of acidic amino acids4
with ionic amino compounds, changes in the structural
properties of the aromatic groups are of interest to design
new analogues. In addition, changes in the polarity and length
of the linkers can lead to a new class of calcimimetic drugs.
Our initial efforts were directed toward the development of
cinacalcet related compounds, which we call class I analogues,
employing enantiopure (R)-1-(naphthalen-1-yl)ethylamine
connected to the aryl group by a propyl linker. The cinacalcet
analogues 11a and 11b were prepared by a two-step route, as is
shown in Scheme 3. First, the racemic and chiral amines were
allowed to react with 3-arylpropionic acids at room temperature
using dicyclocarboxidiimide (DCC) and 4-(N,N-
dimethylamino)pyridine (DMAP), as catalysts.5e The corre-
sponding amides were obtained in excellent yield and high
enantiopurities (>99% ee). Subsequent reduction of the amide
with BH3−THF in THF under reflux conditions afforded the
desired secondary amine in modest to good yield. Calcimimetic
analogues and other related secondary amines can be
conveniently prepared by this facile and simple approach.
As indicated in Table 3, a new family of calcimimetic
analogues (class II) containing the 1-(naphthalen-1-yl)-
ethylamine connected by a propyl linker either to phenoxy or
thiophenoxy groups was prepared. This class of analogues may
provide more polar structural features that can interact with the
calcium-sensing receptors. To our knowledge, there are only
limited examples of this type of calcimimetic analogues.5 In the
Pure (Z)-oximes cannot be obtained directly from their
corresponding ketones because of their thermal instability.
Therefore, different approaches to the (Z)-isomers were
studied.10 Following Sharghi and co-workers’ procedure,10a
acetophenone was treated with hydroxylamine hydrochloride
using K2CO3 under solvent-free conditions. However, the (E)-
acetophenone oxime was the major product. Likewise, the (E)-
isomer was the only product obtained by the method of
Coustard and co-workers using naphthalene and nitroethane in
the presence of H2SO4 to obtain the 1-(naphthalen-1-
yl)ethanone oxime.10b However, the desired (Z)-isomers were
conveniently prepared according to the method first developed
by Smith et al.10c,d Representative (E)-α-bromo acetophenone
oximes and 1-(naphthalen-1-yl)ethanone oxime were synthe-
sized from their corresponding α-bromo ketones by treatment
with 3 equiv of hydroxylamine in methanol/water solvent
(Scheme 2). The corresponding (Z)-acetophenone oximes
were then successfully prepared in excellent yield by the
nucleophilic reaction of α-bromo acetophenone oximes with 1
equiv of NaBH4. It is interesting to note that, in the first step,
no base was required for the oxime formation, and in the
second step, the reaction proceeded very fast at room
temperature. The (Z)-benzyloximes were isolated by column
chromatography and obtained in moderate to high yield
without isomerization from the corresponding 2-bromoketone.
As indicated in Table 2, the pure (Z)-oximes (6) and (Z)-
benzyloximes (7) were obtained in good yields and in high
1
isomeric purities as determined by H and 13C NMR analysis
and GC−MS.
The borane-mediated reductions of (Z)-benzyloximes of
acetophenone of 4-methyl and 4-methoxy acetophenones and
1-(naphthalen-1-yl)ethanone were initially explored to optimize
the reaction conditions catalyzed by spiroborate ester 1 (see
Supporting Information, Table S1). Similarly to the (E)-
benzyloximes, the spiroborate ester 1−BH3−THF system
provided better enantioselectivity than the BH3−Me2S
complex. Interestingly, the optimal catalytic load for the
enantioselective reduction of (Z)-oximes was 15 mol % of
spiroborate 1, slightly higher than it was required for the (E)-
E
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the corresponding amides, which were subsequently reduced
with borane to obtain the desired analogues. In addition, a new
class of calcimimetic analogues (class II), containing a
heteroatom in the linker, was also prepared in good yield and
excellent enantiopurity (>99% ee). This work opens new
avenues for the design of new calcimimetic drugs for the
treatment of hyperparathyroidism.
Table 3. Synthesis of Class II Calcimimetic Analogues
EXPERIMENTAL SECTION
■
Typical Procedure for the Synthesis of E-Oximes. (E)-1-(2-
Methoxyphenyl)ethanone oxime (2a).11a To a mixture of 2-
methoxyacetophenone (10 g, 66 mmol, 1.0 equiv), hydroxylamine-
hydrochloride (4.25 g, 1.0 equiv, 66 mmol) in ethanol (150 mL) was
added dropwise sodium carbonate (0.5 equiv, 33 mmol, 3.45 g) in
water (40 mL). The mixture was then heated at reflux while
maintaining the pH around 5 and monitoring the reaction progress by
TLC. The solvent was then removed under reduced pressure, and the
residue extracted with ethyl acetate (4 × 40 mL). The organic phase
was dried over Na2SO4, filtered and concentrated under reduced
pressure obtaining the crude product (11.1 g) that was recrystallized in
hexane/ethyl acetate (15:1). A white solid was obtained (8.45 g, 78%),
which was analyzed by GC−MS: [10.86 min (3% Z isomer), 11.58
min (97% E isomer)], m/z 165.2, 133.2, 105.2. A sample of this oxime
(3.0 g) was purified by silica gel column chromatography obtaining a
white crystalline solid: mp 205 °C−206 °C; GC−MS [1.82 min (2.0%
a
b
Isolated yield as hydrochloride salt derivatives. The ee value was
1
Z) 12.57 (98% E)] m/z 162.1, 133.1, 105.1, 77.1; H NMR (400
determined by HPLC of the acetamide using a CHIRALCEL OD-H
MHz, CDCl3) δ 2.28 (s, 3H), 3.89 (s, 3H), 7.01 (m, 2H), 7.39 (m,
2H), 9.50 (s, 1H); 13C NMR (100 MHz, CDCl3) δ 15.2, 55.4, 111.1,
120.6, 126.8, 129.4, 130.1, 156.7, 157.4.
column.
(E)-1-(3-Methoxyphenyl)ethanone oxime (2b).11b Clear oil
(3.92 g, 100%): 1H NMR (400 MHz, CDCl3) δ 2.33 (s, 3H), 3.89 (s,
3H), 6.98 (m, 2H), 7.50 (m, 1H), 7.33 (t, J = 8.4 Hz, 1H); 13C NMR
(100 Hz, CDCl3) δ 23.6, 55.4, 112.3, 119.3, 121.1, 129.5, 139.5, 159.9.
(E)-1-(4-Methylthiophenyl)ethanone oxime (2c).11c White
solid (2.06 g, 98%): mp 106−109 °C, Lit.11c 118−120 °C; 1H
NMR (400 MHz, CDCl3,) δ 2.32 (s, 3H), 2.55 (s, 3H), 7.30 (dd, J =
1.6, 7.4 Hz, 2H), 7.60 (dd, J = 1.6, 7.4 Hz, 2H); 13C NMR (100 MHz,
CDCl3) δ 11.9, 15.5, 126.1, 126.3, 133.1, 140.1, 155.6; FT-IR (ν,
cm−1) 2920, 1639, 1466, 1583, 1364; GC−MS m/z 141.0, 124.0, 83.9.
(E)-1-(2-Fluorophenyl)ethanone oxime (2d).11d White crystal-
line solid (1.59 g, 52%): mp 72−73 °C; 1H NMR (400 MHz, CDCl3)
δ 2.35 (s, 3H), 7.15 (m, 2H), 7.39 (m, 1H), 7.50 (m, 1H), 9.75 (s,
1H); 13C NMR (100 MHz, CDCl3) δ 14.7, 116.2, 124.3, 125.07,
129.4, 130.8, 154.0, 159.3, 161.7; GC−MS [9.23 min (97% E isomer)]
m/z 153.1, 136.2, 111.2, 75.2.
first step, representative (3-bromopropoxy)- and (3-bromopro-
pylsulfanyl)-benzene 12 were prepared by the reaction of
phenol or thiophenol with 1,3-dibromopropane in modest to
good yield using sodium hydride as a base. Disubstituted
products and a small amount of disulfide were also observed in
the reaction with thiophenol. Representative calcimimetic
analogues (R)-13 were obtained in good yield without
racemization through the nucleophilic substitution of (3-
bromopropoxy)- and (3-sulfanylpropyl)benzene by the non-
racemic 1-(naphthalen-1yl)ethylamine using triethylamine and
DMAP at 60 °C. Racemic compounds were also prepared in
comparable yields and used for the HPLC analysis of the
enantiopure isomers.
CONCLUSIONS
(E)-1-(4-Fluorophenyl)ethanone oxime (2e).11c White solid
■
(13.9 g, 84%): mp 78−79 °C, Lit.11c 107−108 °C; H NMR (400
1
Enantiomerically pure (S) and (R) primary amines were
conveniently prepared by the borane-mediated reduction of
their corresponding (Z)- and (E)-benzyloxime ethers,
respectively, employing the stable chiral spiroborate ester 1 as
catalyst. In general, the stereoselectivity of the spiroborate ester
1 catalyst for the reduction of the (Z)-isomer was slightly lower
than for the (E)-benzyloxime ethers, and as a consequence,
these processes required somewhat higher amount of catalyst
(i.e., 15%) to achieve similar enantioselectivities to those from
the E isomer, which employed only a 10% catalyst loading.
Overall, no substituent effects on the aromatic ring were
observed in the enantioselective reduction of both E and Z
isomers. The efficiency of the method depends more on the
stereochemical purity of the benzyloxime ether substrates. In
summary, a variety of enantioenriched R and S primary
arylethyl amines were conveniently prepared in high yield using
a mild and environmentally friendly method that can be applied
to the synthesis of important drug intermediates. As examples,
two classes of optically pure calcimimetic analogues were
prepared. For the class I analogues, enantiopure 1-(naphthen-1-
yl)ethylamine was reacted with 3-arylpropionic acids to obtain
MHz, CDCl3) δ 2.33 (s, 3H), 7.12 (m, 2H, 7.66 (m, 2H, 8.92 (s, 1H);
13C NMR (CDCl3, 100 MHz) δ 12.2, 115.4, 127.9 (d, J = 8.0 Hz),
132.7 (d, J = 3.0 Hz), 155.2; 162.2, 164.7 (d, J = 250 Hz); FT-IR (ν,
cm−1) 3217, 2929, 1602, 1511; GC−MS (9.52 min) m/z 153.2, 112.1,
95.1, 75.1.
(E)-1-(2-Bromophenyl)ethanone oxime (2f).11e The product
was recrystallized in hexane/ethyl acetate (9:1) obtaining a white
crystalline solid (5.5 g, 89%) containing 10% of the Z isomer by GC−
MS. A sample of 2 g of product was recrystallized in ethanol−water
(3:1): mp 129 °C−131 °C, Lit.11e 112−114 °C; 1H NMR (400 MHz,
CDCl3) δ 2.31 (s, 3H), 7.29 (m, 1H), 7.37 (m, 2H) 7.65 (m, 1H),
78.33 (s, 1H); 13C NMR (100 MHz, CDCl3) δ 15.9, 121.7, 127.4,
130.1, 130.1, 138.8, 158.1; GC−MS [9.23 min (97% E)] m/z 153.1,
136.2, 111.2, 75.2.
(E)-1-(4-Bromophenyl)ethanone oxime (2g).11f White crystal-
line solid (8.9 g, 84%): mp 119−121 °C, Lit.11f 127−129 °C; 1H NMR
(400 MHz, CDCl3) δ 2.62 (s, 3H), 7.65 (m, 2H), 7.85 (m, 2H); 13C
NMR (100 MHz, CDCl3) δ 11.9, 123.5, 127.6, 131.6, 135.4, 155.2;
GC−MS [12.65 min (E)] m/z 214, 212, 155, 106.1, 102.1.
(E)-1-(3,4-Difluorophenyl)ethanone oxime (2h).11g White
1
crystalline solid (3.0, 76%): mp 76−77 °C; H NMR (400 MHz,
CDCl3, 100 MHz) δ 2.30 (s, 3H), 7.22 (m, 1H), 7.31 (s, 1H), 7.53 (m,
F
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1H), 7.51 (m, 1H); 13C NMR (CDCl3, 100 MHz) δ 12.0, 115.2 (m,
Hz), 117.3 (d, J = 17 Hz), 122.3 (m, J = 3.5 Hz, CH), 133.5 (m, J =
3.5 Hz), 149.5 (d, J = 11.5 Hz), 151.9 (d, J = 12 Hz), 154.3; FT-IR (ν,
cm−1) 31745, 3083, 2856, 1541, 1422, 1314, 1366, 891 and 813.
(E)-1-(3,5-bis(Trifluoromethyl)phenyl)ethanone oxime
(2i).11h White crystalline solid (3.9, 82%): mp 108−111 °C; 1H
NMR (400 MHz, CDCl3,) δ 2.39 (s, 3H), 7.93 (s, 1H), 8.13 (s, 2H),
8.50 (s, 1H); 13C NMR (100 MHz, CDCl3,) δ 11.8, 126.1−119.1 (q, J
= 271 Hz), 122.7 (m, J = 4 Hz), 126.1 (d, J = 4 Hz), 131.8 (q, J = 33
Hz), 138.5; GC−MS [8.84 min (E)] m/z 571.0, 254.0, 213.0, 202.2.
(E)-1-(2-Fluoro-4-methoxyphenyl)ethanone oxime (2j).11i
After the above-described workup and purification, the product was
isolated as a white crystalline solid (4.1 g, 93%): mp 106−107 °C; 1H
NMR (400 MHz, CDCl3) δ 2.32 (s, 3H), 3.86 (s, 3H), 3.73 (m, 2H),
6.71 (m, 2H), 7.44 (t, 1H, J = 8.6 Hz), 9.33 (s, 1H); 13C NMR (100
MHz, CDCl3) δ 14.6, 55.6, 102.2 (d, J = 21 Hz), 110.1 (d, J = 12 Hz),
117.5 (d, J = 12 Hz), 129.9 (d, J = 5 Hz), 153.7 (d, J = 3 Hz), 161.5,
162.5 (d, J = 249 Hz), 161; GC−MS [12.24 min, E isomer] m/z 183.2,
166.2, 151.2, 126.2, 122.2.
1378, 1432, 1457, 1511, 1651, 2862, 3043, 3177; GC−MS m/z 149.2
(M+).
(Z)-1-(4-Methoxyphenyl)ethanone oxime (6c)..7k,10f White
1
solid (1.23 g, 58%): mp 66−68 °C; H NMR (400 MHz, CDCl3) δ
2.19 (s, 3H), 3.83 (s, 3H), 6.94 (d, J = 8.8 Hz, 2H), 7.60 (d, J = 8.8
Hz, 2H), 8.12 (br s, 1H); 13C NMR (400 MHz, CDCl3) δ 21.5, 55.3,
113.5, 125.9, 129.9, 154.0, 160.0; FT-IR (ν, cm−1) 677, 838, 945, 1021,
1121, 1184, 1249, 1311, 1406, 1509, 1572, 1603, 1631, 1978, 2837,
2997, 3176; GC−MS m/z 165.3 (M+).
(Z)-1-(3-Methoxyphenyl)ethanone oxime (6d). Light yellow
1
liquid (0.72 g, 74%): H NMR (400 MHz, CDCl3) δ 2.20 (s, 3H),
3.81 (s, 3H), 6.91−6.94 (m, 1H), 7.08−7.10 (m, 2H), 7.32−7.36 (m,
1H), 8.93 (br, 1H); 13C NMR (CDCl3) δ 21.5, 55.1, 113.4, 114.4,
119.8, 129.1, 135.0, 154.4, 159.1; FT-IR (ν, cm−1) 781, 855, 940, 1034,
1181, 1227, 1288, 1427, 1487, 1578, 1599, 1659, 1704, 2917, 3232;
GC−MS m/z 165.3 (M+).
(Z)-1-(4-Chlorophenyl)ethanone oxime (6e)..7k,10f White solid
(1.7 g, 82%): mp 111−113 °C, Lit.10f 94 °C mixture of 95% Z and E);
1H NMR (400 MHz, CDCl3) δ 2.16 (s, 3H), 7.34 (d, J = 8.4 Hz, 2H),
7.48 (d, J = 8.4 Hz, 2H), 8.62 (s, 1H); 13C NMR (400 MHz, CDCl3) δ
21.4, 128.5, 129.5, 132.0, 135.0, 153.5; GC−MS m/z 169.1 (M+).
(Z)-1-(4-Bromophenyl)ethanone oxime (6f).10f White solid
(1.04 g, 79% overall from α-bromo-4-bromo acetophenone): mp 112−
115 °C; 1H NMR (400 MHz, CDCl3) δ 2.17 (s, 3H), 7. 43 (d, J = 8.8
Hz, 2H), 7.48 (d, J = 9.2 Hz, 2H), 8.14 (s, 1H); 13C NMR (400 MHz,
CDCl3) δ 21.4, 123.3, 129.7, 131.4, 132.5, 153.7; GC−MS m/z 213.1
(M+).
(E)-1-(Naphthalen-1-yl)ethanone oxime (2k).11j White crystal-
line solid (11.4 g, 72%): mp 134−141 °C, Lit.11j 136−138 °C; H
1
NMR (400 MHz, DMSO-d6) δ 2.3 (s, 3H), 2.4 (s, 3H), 3.9 (s, 3H),
8.2−7.4 (m, 7H), 9.2 (s, 1H); 13C NMR (100 MHz, DMSO-d6) δ
16.8, 125.2, 125.3, 126.0, 126.1, 126.6, 128.5, 129.2, 130.9, 133.9,
135.5, 157.5, GC−MS [14.46 min (9% Z isomer), 15.18 min (91% E
isomer)] m/z 185.1, 168.2, 127.2.
Typical Procedure for the Preparation of (Z) Oximes from
the Ketone.10c,d (Z)-1-(Naphthalen-1-yl)ethanone oxime (6i). 1-
Acetylnaphthalene (3.4 g, 0.02 mol) was placed in a 125 mL round-
bottomed flask and dissolved in 20 mL of CH2Cl2. A solution of
bromine (3.2 g, 1.03 mL, 0.02 moL) in 20 mL of CH2Cl2 was added
dropwise via a syringe pump to the 1-acetylnaphthalene solution under
stirring at 0 °C. After the addition, the mixture was stirred for 1 h and
distilled under reduced pressure on a water bath to obtain a red
viscous liquid (5.38 g, 21.3 mmol). Immediately, the 2-bromo-
substituted ketone was reacted with NH2OH−HCl (4.5 g, 65 mmol)
in water (6 mL) and MeOH (40 mL) until a clear solution was
obtained. The reaction mixture was left stirring overnight at 25 °C or
until completion was indicated by TLC. Then, the solvent was
removed under a vacuum to yield a dark brown viscous oil. The crude
(Z)-2-bromo-1-(naphthalen-1-yl)ethanone oxime (10.0 g, 37.9 mmol)
was dissolved in acetonitrile (60 mL) and added portion-wise to a
stirred mixture of NaBH4 (1.43 g, 37.9 mmol) in water/acetonitrile
(200 mL/60 mL). Rapid evolution of gas formation was noted, and
after 10 min the reaction was complete by TLC analysis. Water (60
mL) was added, and the mixture was extracted with EtOAc (3 × 90
mL). The combined organic phase was washed with saturated NaCl
solution (2 × 60 mL) and dried over anhydrous Na2SO4. The solvents
were removed by rotary evaporation to yield the crude product (9.7 g).
The crude product was purified by silica gel column chromatography,
obtaining the pure product as a brown viscous liquid (4.6 g, 72%
(Z)-1-(3-Bromophenyl) ethanone oxime (6g).12 Light yellow
1
liquid (0.7 g, 55%): H NMR (400 MHz, CDCl3) δ 2.18 (s, 3H),
7.25−7.30 (m, 1H), 7.44−7.51 (m, 2H), 7.69 (s, 1H), 8.68 (s, 1H);
13C NMR (CDCl3) δ 21.2, 122.1, 126.3, 129.6, 130.70, 131.87, 135.5,
153.1; FT-IR (ν, cm−1) 779, 942, 1020, 1282, 1374, 1414, 1473, 1560,
1650, 1704, 2860, 3216; GC−MS m/z 213.1 (M+).
(Z)-1-(4-Nitrophenyl)ethanone oxime (6h).13 Light yellow
solid (0.816 g, 74%): mp 174−175 °C; 1H NMR (400 MHz,
CDCl3) δ 2.24 (s, 3H), 7.51 (br s, 1H), 7.65−7.68 (m, 2H), 8.26−8.28
(m, 2H); 13C NMR (CDCl3) δ 21.5, 123.6, 123.9, 127.0, 129.1, 140.4,
153.4; FT-IR (ν, cm−1) 693, 754, 854, 945, 1026, 1084, 1109, 1340,
1395, 1514, 1602, 3189.
General Procedure for the Synthesis of (E) or (Z)-O-
Benzyloxime Ethers 7..8,14−19 To a suspension of NaH (1.1
equiv) in DMF, a solution of oxime (1 equiv) was added dropwise by a
syringe pump at 0 °C, and the reaction mixture was stirred for 1 h at 0
°C. A solution of PhCH2Br (1.05 equiv) in DMF was added dropwise
via a syringe pump. The resulting mixture was stirred overnight at
room temperature, quenched with saturated aqueous NH4Cl solution
and extracted with ether or ethyl acetate. The organic phases were
combined and dried over anhydrous Na2SO4. The solvent was
evaporated under a vacuum, and the residue was purified by column
chromatography on silica gel or preparative TLC plates to afford the
desired pure benzyloximes.
1
(E)-1-(2-Methoxyphenyl)ethanone O-benzyloxime (3a). The
crude product was purified by silica gel column chromatography (35.8
g, length 12.3 cm, diameter 1.6 cm) with petroleum ether/ethyl acetate
(18:1). The fractions 1−9 were transferred to a round bottomed flask
overall from 1-acetonaphthone): H NMR (400 MHz, CDCl3) δ 2.22
(s, 3H), 7.26−7.28 (m, 1H), 7.46 (m, 3H), 7.73 (m, 1H), 7.82 (m,
2H), 9.41(s, 1H); 13C NMR (400 MHz, CDCl3) δ 22.4, 123.6, 125.1,
125.2, 125.9, 126.3, 128.3, 128.5, 128.8, 133.2, 133.9, 155.7; FT-IR (ν,
cm−1) 775, 800, 939, 1021, 1098, 1251, 1386, 1434, 1658, 3231; GC−
MS m/z 185.1 (M+).
1
and concentrated to obtain a clear oil (2.38 g, 80%): H NMR (400
MHz, CDCl3) δ 2.29 (s, 3H), 3.88 (s, 3H), 5.29 (s, 2H), 6.98 (m, 1H)
7.01 (d, J = 1.2 Hz, 1H), 7.33 (m, 3H), 7.40 (m, 2H), 7.5 (m, 2H);
13C NMR (100 MHz, CHCl3) δ 16.37, 55.5, 75.9, 111.1, 120.6, 127.1,
128.12, 128.3, 129.7, 130.2, 138.2, 157.1, 57.5; FT-IR (ν, cm−1) 1578,
1238, 919, 751, 641; HRMS (ESI-TOF) m/z [M + H]+ Calcd for
C16H18NO2 256.1332, found 256.1333.
(Z)-Acetophenone oxime (6a).10d After following the typical
procedure, the crude product was purified by silica gel column
chromatography affording the Z isomer (0.87 g, 71%) and the E-
isomer (0.25 g). The Z product was a white solid: mp 81−83 °C,
Lit.10d 81−83 °C; 1H NMR (400 MHz, CDCl3) δ 2.20 (s, 3H), 7.35−
7.39 (m, 3H), 7.42−7.43 (m, 2H), 7.44 (br s, 1H); GC−MS m/z
135.1 (M+).
(E)-1-(3-(Methoxyphenyl)ethanone O-benzyloxime (3b).
1
Clear oil (2.15 g, 93%): H NMR (400 MHz, CDCl3) δ 2.39 (s,
(Z)-1-(p-Tolyl)ethanone oxime (6b).10f White solid (1.21 g,
87%): 1H NMR (400 MHz, CDCl3) δ 2.19 (s, 3H), 2.38 (s, 3H), 7.34
(d, J = 8.0 Hz, 2H), 7.48 (d, J = 8.2 Hz, 2H), 8.61 (s, 1H); 13C NMR
(400 MHz, CDCl3) δ 21.4, 21.6, 127.9, 128.9, 130.9, 139.2, 154.6,
154.7; FT-IR (ν, cm−1) 673, 721, 815, 959, 1033, 1088, 1188, 1295,
3H), 3.92 (s, 3H), 3.39 (s, 3H), 7.02 (m, 1H), 7.45 (m, 8H); 13C
NMR (100 MHz, CDCl3) δ 13.0, 55.3, 76.3, 111.6, 114.9, 118.8, 127.8,
128.2, 128.4, 129.4, 138.2, 154.8, 159.7; FT-IR (ν, cm−1) 2834, 1598,
1229, 981, 731; HRMS (ESI-TOF) m/z [M + H]+ Calcd for
C16H18NO2 256.1332, found 256.1343.
G
dx.doi.org/10.1021/jo400371x | J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Article
(E)-1-(4-Methylthiopheneyl)ethanone O-benzyloxime (3c).
The solid was purified by silica gel column chromatography with
hexane/ethyl acetate (9:1 v/v) as eluant obtaining white crystals (1.37
g, 50%): mp 74−75 °C; 1H NMR (400 MHz, CDCl3) δ 2.30 (s, 3H),
2.54 (s, 3H), 5.29 (s, 2H), 7.29 (d, J = 8.2 Hz), 7.42 (m, 5H), 7.63 (d,
J = 8.4 Hz); 13C NMR (CDCl3, 100 MHz) δ 12.7, 15.5, 76.2, 126.0,
126.4, 127.7, 128.1, 128.3, 133.3, 138.1, 139.8, 154.4; FT-IR (ν, cm−1)
1598, 1491, 1023, 819, 699; HRMS (ESI-TOF) m/z [M + H]+ Calcd
for C16H18NOS 272.1104, found 272.1105.
17.6, 76.1, 76.8, 77.1, 77.4, 76.1, 125.2, 125.6 126.0, 126.5, 127.9,
129.3, 128.4, 128.5, 129.1, 130.9, 133.9, 135.5, 138.3, 157.0.
(Z)-Acetophenone O-benzyloxime (7a).23 The product was
1
purified by preparative TLC as a yellow oil (0.785 g, 58%): H NMR
(C6D6) δ 2.07 (s, 3H), 5.23 (s, 2H), 7.14−7.23 (m, 6H), 7.27(m, 2H),
7.39 (m, 2H); 13C NMR (C6D6) δ 21.3, 75.9, 128.0, 128.1, 128.2,
128.3, 128.5, 128.7, 134.8, 138.8, 153.2; FT-IR (ν, cm−1) 692, 736,
764, 881.9, 1039, 1114, 1208, 1364, 1434, 1495, 1607, 2918, 3031;
GC−MS m/z 225.2 (M+), 118.1, 91.1.
1-(2-Fluorophenyl)ethanone O-benzyloxime (3d).6b The
product was purified over silica gel (36 g) using hexane and ethyl
acetate (12:1 v/v) as mobile phase obtaining an oil (1.49 g, 67%): 1H
NMR (CDCl3, 400 MHz) δ 2.37 (s, 3H) 5.33 (s, 2H) 7.20 (m, 2H),
7.38 (m, 7H); 13C NMR (CDCl3, 100 MHz) δ 15.8, 76.3, 116.2, 116.0
(d, J = 4 Hz) 125.2, 125.3 (d, J = 13 Hz), 127.8, 128.1, 128.4, 129.7,
129.7 (d, J = 3 Hz) 130.6, 130.5 (d, J = 9 Hz), 137.9, 153.7, 153.7 (d, J
= 1 Hz), 161.9, 159.4 (d, J = 2.49 Hz); GC−MS (tR 15.28 min) m/z
146.2, 138.2, 137.2, 91.2, 65.2.
(Z)-1-(p-Tolyl)ethanone O-benzyloxime (7b). The product was
purified by silica gel column chromatography as a yellow oil (1.34 g,
1
68%): H NMR (C6D6) δ 2.12 (s, 3H), 2.14 (s, 3H), 5.27 (s, 2H),
7.03−7.05 (m, 2H), 7.14−7.18 (m, 1H), 7.22−7.27 (m, 2H), 7.44 (d, J
= 7.2 Hz, 2H), 7.58 (d, J = 7.2 Hz, 2H); 13C NMR (C6D6) δ 21.0,
21.2, 76.0, 76.2, 127.2, 127.5, 127.6, 127.8, 128.5, 128.7, 128.8, 128.9,
131.9, 138.5, 138.9, 153.0, 160.1; GC−MS m/z 239.3 (M+), 132.3 (M+
− OBn), 91.2.
(Z)-1-(4-Methoxyphenyl)ethanone O-benzyloxime (7c). The
product was purified by silica gel column chromatography as a yellow
oil (1.1 g, 58%): 1H NMR (C6D6) δ 2.14 (s, 3H), 3.34 (s, 3H), 5.30 (s,
2H), 6.79−6.82 (m, 2H), 7.17−7.19 (m, 1H), 7.23−7.27 (m, 3H),
7.44−7.46 (m, 2H), 7.68−7.71 (m, 2H); 13C NMR (C6D6) δ 21.1,
54.5, 76.1, 113.3, 113.7, 126.7, 127.1, 127.6, 127.7, 127.8, 128.3, 128.5,
130.4, 138.9, 152.1, 160.1; FT-IR (ν, cm−1) 696, 732, 830, 882, 927,
1006,1029, 1104, 1181, 1258, 1304, 1372, 1437, 1454, 1509, 1605,
2919, 3030.7; GC−MS m/z 255.2 (M+), 225.2, 91.1.
(Z)-1-(3-Methoxyphenyl)ethanone O-benzyloxime (7d). Yel-
low oil (0.67 g, 75%): 1H NMR (CDCl3) δ 2.16 (s, 3H), 3.73 (s, 3H),
5.09 (s, 2H), 6.84−6.87 (m, 1H), 7.02−7.06 (m, 2H), 7.25−7.30 (m,
6H); 13C NMR (CDCl3) δ 21.9, 55.3, 76.0, 113.8, 114.7, 120.3, 127.7,
128.0, 128.4, 129.3, 135.9, 138.4, 154.2, 159.3; FT-IR (ν, cm−1) 694,
734, 782, 875, 909, 931, 1036, 1083, 1112, 1182, 1228, 1287, 1365,
1429, 1453, 1468, 1578, 1598, 1682, 2919, 3030; GC−MS m/z 254.3
(M+), 91.1; HRMS (ESI-TOF) m/z [M + Na]+ Calcd. for
C15H14BrNONa 396.1546, found 396.1546.
(E)-(1-(4-Fluorophenyl)ethanone O-benzyloxime (3e).7k The
product was purified by silica gel column chromatography (50 g) using
hexane/ethyl acetate (20:1 v/v) to give a white solid (4.05 g, 84%):
mp 43−45 °C, Lit.7k 58−60 °C; H NMR (400 MHz, CDCl3, 400
1
MHz) δ 2.31 (s, 3H), 5.29 (s, 2H), 7.10 (m, 2H), 7.43 (m, 5H), 7.67
(s, 2H); 13C NMR (CDCl3, 100 MHz) δ 76.3, 115.3 (d), 127.9 (d)
154.1, 162.2, 164.7 (d, J = 250 Hz); FT-IR (ν, cm−1) 2919, 1611,
1508, 1403; GC−MS m/z 244.2, 213.3, 136.2, 91.3.
(E)-1-(2-Bromophenyl)ethanone O-benzyloxime (3f).6b The
product was purified by silica gel column chromatography (20 g, long
11.7 cm, diam 0.75 cm) with hexane/ethyl acetate (20:1). The
fractions 2−5 were collected and concentrated to obtain a light yellow
1
oil (1.05 g, 87%): H NMR (400 MHz, CDCl3) δ 2.33 (s, 3H), 5.31
(s, 2H), 7.25 (m, 1H), 7.33 (m, 3H), 7.46 (m, 4H), 7.64 (dd, J = 1.2
Hz, J = 8.0 Hz, 1H); 13C NMR (100 MHz, CHCl3) δ 16.92, 76.1,
121.9, 127.4, 127.8, 128.0, 130.0, 133.1, 138.0, 138.9, 157.1; FT-IR (ν,
cm−1) 3031, 2922, 1364, 1012, 752, 695.
(Z)-1-(4-Chlorophenyl)ethanone O-benzyloxime (7e). The
product was purified by preparative TLC as a yellow oil (0.98 g,
63%): 1H NMR (CDCl3) δ 2.16 (s, 3H), 5.09 (s, 2H), 7.26−7.34 (m,
7H), 7.43−7.44 (m, 2H); 13C NMR (CDCl3) δ 21.6, 76.1, 127.7,
127.9, 128.3, 128.4, 129.6, 132.7, 134.8, 138.1, 152.8; FT-IR (ν, cm−1)
733, 766, 826, 884, 931, 1012, 1038, 1091, 1104, 1208, 1289, 1307,
13645, 1398, 1433, 1454, 1489, 1593, 2918, 3032; GC−MS m/z 258.2
(M+), 91.1.
(E)-1-(4-Bromophenyl)ethanone O-benzyloxime (3g).20
White crystals purified by recrystallization (3.53 g, 58%): mp 58−59
1
°C; H NMR (400 MHz, CDCl3) δ 2.29 (s, 3H), 5.29 (s, 2H), 7.42
(m, 5H), 7.53 (m, 4H); 13C NMR (100 MHz, CDCl3) δ 12.6,
123.3,127.6, 127.8, 128.2, 128.4, 131.5, 135.5, 137.9, 153.9.
(E)-1-(3,4-Difluorophenyl)ethanone O-benzyloxime (3h). Pu-
rified by silica gel column chromatography as a clear oil (2.52 g, 94%):
1H NMR (400 MHz, DMSO-d6) δ 2.29 (s, 3H), 5.31 (s, 2H), 7.20 (m,
(Z)-1-(4-Bromophenyl)ethanone O-benzyl oxime (7f).20
1H), 7.43 (m, 6H); 13C NMR (100 MHz, DMSO-d6) δ 12.5, 76.5,
115, 152; GC−MS m/z 261.3, 231.2, 91.2 [13.70 min (2% Z), 15.62
min (98% E)]; HRMS (ESI-TOF) m/z [M + H]+ Calcd for
C15H13F2NO 262.1038, found 262.1041.
1
Yellow oil (0.79 g, 70%): H NMR (C6D6) δ 1.95 (s, 3H), 5.20 (s,
2H), 7.16−7.30 (m, 7H), 7.36−7.38 (m, 2H); 13C NMR (C6D6) δ
20.9, 76.2, 122.9, 127.6, 128.0, 128.1, 128.3, 128.4, 129.9, 131.2, 133.2,
138.4, 152.0; FT-IR (ν, cm−1) 732, 821, 884, 908, 1008, 1038, 1070,
1101, 1208, 1288, 1307, 1364, 1395, 1434, 1454, 1486, 1588, 2918,
3031; GC−MS m/z 303.2 (M+), 91.1.
(E)-1-[3,5-bis(Trifluoromethyl)phenyl]ethanone O-benzylox-
ime (3i).21 The crude product was purified by flash silica gel column
chromatography to give a clear oil (3.2 g, 86%): 1H NMR (400 MHz,
CDCl3) δ 2.36 (s, 3H), 5.55 (s, 2H), 7.46 (m, 5H), 7.91 (s, 1H), 8.16
(s, 2H); 13C NMR (100 MHz, CDCl3) δ 12.5, 119−127.3 (q, J = 121
Hz), 122.4 (m, J = 4 Hz), 126.0 (d, J = 3 Hz), 128.1, 128.3, 128.5,
131.8 (q, J = 33 Hz), 137.4, 138.6, 152.1; GC−MS (tR 14 min) mz
362.2, 213.1, 151.1, 91.1, 77.2.
(Z)-1-(3-Bromophenyl)ethanone O-benzyloxime (7g). Yellow
1
oil (0.59 g, 71%): H NMR (CDCl3) δ 2.21 (s, 3H), 5.22 (s, 2H),
7.17−7.36 (m, 8H), 7.46 (s, 1H); 13C NMR (CDCl3) δ 12.9, 76.3,
122.8, 124.9, 128.1, 128.4, 128.6, 129.3, 130.1, 132.1, 138.0, 138.9,
153.8; IR (ν, cm−1) 692, 733, 886, 908, 933, 996, 1038, 1070, 1116,
1209, 1281, 1364, 1433, 1454, 1472, 1559, 1591, 1723, 2922, 3031;
GC−MS m/z 304.1(M+), 91.1; HRMS (ESI-TOF) m/z [M + H ]+
Calcd for C15H15BrNO 304.03370, found 304.03370.
(E)-1-(2-Fluoro-4-methoxyphenyl)ethanone O-benzyloxime
1
(3j). Purified by column chromatography as an oil (3.8 g, 79%): H
(Z)-1-(4-Nitrophenyl)ethanone O-benzyloxime (7h).7j Yellow
NMR (400 MHz, CDCl3) δ 2.33 (s, 3H), 3.85 (s, 3H), 5.30 (s, 2H),
6.70 (m, 2H), 7.4 (m, 6H); 13C NMR (100 MHz, CDCl3) δ 15.6, 55.3,
76.1, 102.1 (d, J = 25 Hz), 110.1 (d, J = 3.0 Hz), 117.7 (d, J = 13 Hz),
127.8, 128.1, 128.4, 128.5, 130.2 (d, J = 5 Hz), 130.1, 153.5 (d, J = 1
Hz), 160.2, 161.5 (d, J = 11 Hz), 162.7; GC−MS m/z [17.87 min]
273.1, 91.1, 65.1; HRMS (ESI-TOF) m/z [M + H]+ Calcd for
C16H16NO2F 274.1238, found 274.1250.
1
oil (0.87 g, 71%): H NMR (CDCl3) δ 2.22 (s, 3H), 5.11 (s, 2H),
7.25−7.34 (m, 5H), 7.61−7.63 (m, 2H), 8.22−8.24 (m, 2H); 13C
NMR (CDCl3) δ 21.6, 76.5, 123.6, 128.0, 128.1, 128.6, 129.1, 137.8,
141.0, 147.8, 152.4; FT-IR (ν, cm−1) 694, 734, 750, 854, 887, 910, 933,
1012, 1038, 1113, 1179, 1209, 1302, 1344, 1433, 1454, 1493, 1517,
1596, 2924, 3033; GC−MS m/z 268.2 (M+), 91.1.
(E)-1-Naphthalen-1-yl-ethanone O-benzyloxime (3k).22 The
product was purified by silica gel (60 g) flash column chromatography
using hexane/ethyl acetate (17:1 V/V) as a white solid (5.12 g, 74%):
(Z)-1-(Naphthalen-1-yl)ethanone O-benzyloxime (7i). The
crude product was first purified by column chromatography on silica
gel and then recrystallized in hexane to obtain a white solid (4.1 g,
1
1
mp 36−37 °C; H NMR (400 MHz, CDCl3) δ 2.47 (s, 3H), 5.37 (s,
60%): mp 56−57 °C; H NMR (400 MHz, CDCl3) δ 2.13 (s, 3H),
2H), 7.4−7.5 (m, 9H), 7.89 (m, 3H); 13C NMR (CDCl3, 100 MHz) δ
5.10 (s, 2H), 7.14−7.20 (m, 3H), 7.25 (m, 4H), 7.3 (m, 2H), 7.35 (m,
H
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20
1H), 7.36 (m, 1H), 7.37 (m, 1H); 13C NMR (400 MHz, CDCl3) δ
22.3, 75.7, 123.7, 125.2, 125.9, 126.0, 126.2, 127.4, 127.6, 127.7, 127.8,
128.1, 128.3, 128.4, 129.5, 133.7, 135.5, 138.9, 154.7; FT-IR (ν, cm−1)
777, 803, 876, 971, 1025, 1038, 1208, 1369, 1438, 1504, 1590, 1626,
3362; GC−MS m/z 274.2 (M+), 91.2; HRMS (ESI-TOF) m/z [M +
H]+ Calcd for C19H18NO 276.1383, found 276.1388.
mL/min, tR 51.24 min (97.2%) and 61.28 min (2.7%)] 95% ee; [α]D
−121 (c 1.4, CHCl3), Lit.29 [α]D = −104.8 (c 0.28, CHCl3); H
NMR (400 MHz, CDCl3) δ 1.53 (s, 3H), 2.03 (s, 3H), 5.16 (m, 1H),
5.71 (s, 1H), 7.07 (m, 2H), 7.32 (t, 2H); 13C NMR (100 MHz,
CDCl3) δ 21.7, 23.5, 48.2, 76.7, 77.0, 77.2, 77.36, 115.4, 115.6, 127.8,
127.9, 139.0, 139.0, 160.8, 163.2, 169.0; FT-IR (v, cm−1) 3254, 3070,
2976, 1638, 1554, 1509, 831.
25
1
General Procedure for the Asymmetric Reduction of (E)-
Benzyloximes with Spiroborate 1 as Catalyst..8a,17 To an oven-
dried test tube under a N2 atmosphere, 10% of catalyst EG-DPV
catalyst 1 (33 mg, 0.1 mmol) was added and dissolved in anhydrous
1,4-dioxane (5 mL). A solution of BH3−THF (4 mL, 1 M, 4 mmol)
was added, and the solution was stirred for 30 min. The solution was
cooled at 0 °C, and O-benzyloxime (1.0 mmol) dissolved in 1,4-
dioxane (5 mL) was added at a slow rate via a syringe. After 72 h, the
reaction was quenched with methanol (5 mL), The solution was
refluxed for 4 h, and the solvent was removed under reduced pressure.
Water (10 mL) was added, and the aqueous solution was extracted
with diethyl ether (3 × 25 mL). The organic phase was collected, dried
over potassium carbonate, and the solvent removed under a vacuum.
To the crude product dissolved in dry CH2Cl2 (10 mL) were added
triethylamine Et3N (417 μL, 3.0 mmol), acetic anhydride (284 μL, 3.0
mmol) and a small crystal of DMAP (N,N-dimethylamino pyridine).
The reaction mixture was stirred overnight at room temperature. The
mixture was transferred to a separatory funnel and extracted with water
(10 mL) and brine (7 mL). The organic phase was collected, dried
over Na2SO4, filtered and concentrated under a vacuum. The crude
acetamide derivative was purified by silica gel column chromatography
or preparative TLC, and the enantiopurity was analyzed by GC using
the Chrompack Chiralsil-Dex-CB column (30 m × 25 mm × 0.25 μm)
or by HPLC with Chiral Cell OD-H or Chiral Pack AD-H columns.
(S)-N-[1-(2-Methoxyphenyl)ethyl] acetamide (5a).25 The
crude product was purified by preparative TLC using petroleum
ether/ethyl acetate (2:1 v/v) obtaining a white solid (252 mg, 88%):
mp 155−157 °C, Lit.25 142−144 °C; chiral GC [method isothermal
(S)-N-[1-(2-Bromo-phenyl)ethyl] acetamide (5f).30 White solid
(289 mg, 80%): mp 155−157 °C: HPLC [Chiral Cell OD-H column,
method hexane/isopropyl alcohol (85:15), flow 0.5 mL/min, tR 11.4
min (0.75%), 14.4 (99.25%)] 97% ee; [α]20 = −4.0 (c 2.0, CHCl3);
D
1H NMR (400 MHz, CDCl3) δ 1.52 (d, J = 7.2 Hz, 3H), 2.04 (s, 3H),
5.39 (m, 1H), 5.90 (s, 1H), 7.16 (m, 1H), 7.36 (m, 2H); 13C NMR
(100 MHz, CDCl3) δ 21.0, 23.3, 49.2, 123.0, 127.2, 127.7, 128.8,
133.5, 142.0, 168.9; FT-IR (ν, cm−1, ATR) 3277, 1647, 1546, 1374.
(S)-N-[1-(4-Bromophenyl)ethyl] acetamide (5g).31 White solid
(301 mg, 83%): mp 155−157 °C; chiral GC [gradient method 90 °C/
10 min, 4 °C/min up to 190 °C, 190 °C/35 min (70 min), tR 34.4 min
(97.7%), 35.3 (2.3%)] 95.4% ee; [α]20 = −85 (c 1.2, CHCl3); H
1
D
NMR (400 MHz, CDCl3) δ 1.50 (d, J = 6.8 Hz, 3H), 2.03 (s, 3H),
5.12 (m, 1H), 5.73 (s, 1H), 7.24 (d, J = 6.8 Hz), 7.50 (d, J = 6.4 Hz,
2H); 13C NMR (100 MHz, CDCl3) δ 21.6, 23.4, 48.2, 121.1, 127.9,
131.7, 142.3, 169.1.
(S)-N-[1-(3,4-Difluorophenyl)ethyl]-acetamide (5h).32 The
crude product was purified by preparative TLC using hexane/ethyl
acetate (3:2) obtaining a white solid (253 mg, 84%): mp 88−90 °C;
chiral GC [gradient method 90 °C/10 min, 4 °C/min until 190 °C,
190 °C/35 min (70 min), tR 26.68 min (96%), 27.2 min (4%)] 92% ee;
[α]20D = −36 (c 1.1, CHCl3); 1H NMR (400 MHz, CDCl3) δ 1.50 (d,
J = 6.8 Hz, 3H,), 2.03 (s, 3H), 5.11 (q, J = 7.2 Hz, 1H), 5.84 (s, 1H),
7.07 (m, 1H), 7.15 (m, 2H); 13C NMR (100 MHz, CDCl3) δ 21.7,
23.3, 47.9, 115.1 (d, J = 17 Hz), 117.3 (d, J = 17 Hz), 122.1 (q, J = 3
Hz), 140.5 (t, J = 4.5 Hz), 148.1−149.1 (dd J1 = 13 Hz, J2 = 86 Hz)
151.6−150.6 (dd, J = 87 Hz, J = 13 Hz), 169.2; FT-IR (ν, cm−1) 3256,
1609, 1551, 1274, 1114; HRMS (ESI-TOF) m/z [M + Na]+ Calcd for
C10H11F2NaO 222.0701, found 222.0705.
120 °C, tR 46.8 min (98.9%), 48.4 (1.1%)] 98% ee; [α]20 = −9.6 (c
D
1
11.0, CHCl3), Lit25 [α]20 = −38.3 (c 1.69, EtOH); H NMR (400
D
MHz, CDCl3) δ 1.49 (d, J = 6.8 Hz, 3H), 2.01 (s, 3H), 3.93 (s, 3H),
5.31 (q, J = 7.2 Hz, 1H), 5.45 (s, 1H), 6.96 (m, 2H), 7.27 (m, 1H);
13C NMR (100 MHz, CDCl3) δ 21.4, 23.8, 47.5, 55.3, 111.1, 120.9,
128.1, 128.4. 130.8, 157.1, 168.7; FT-IR (ν, cm−1) 3313, 1642, 1436,
1240.
(S)-N-[1-(3,5-Bistrifluoromethylphenyl)ethyl] acetamide
(5i).32 White solid (0.348 g, 78%): mp 88−90 °C; chiral GC [method
isothermal 110 °C/flow = 0.8 mL/min, tR 25.4 min, 1.8%, 26.17 min
1
98.1%] 92% ee; [α]20 = −58 (c 1.1, CHCl3); H NMR (CDCl3.400
D
MHz) δ 1.57 (d, J = 7.2 Hz, 3H), 2.07 (s, 3H), 5.24 (m, J = 7.2 Hz,
1H), 5.98 (s, 1H), 7.81 (d, J = 7.6 Hz, 3H); 13C NMR (CDCl3, 100
MHz) δ 21.9, 23.3, 48.4, 121.3 (t, J = 4 Hz), 121.9, 124.6, 126.3. 131.8
(t, J = 34 Hz), 146.2, 169.4; GC−MS (tR 10.83 min) m/z 299.2, 256.1,
242.1, 240.1, 188.2, 72.1.
(S)-N-[1-(3-Methoxyphenyl)ethyl] acetamide (5b).26 The
crude acetamide was purified by preparative TLC using petroleum
ether/ethyl acetate (3:1) as an oil (256 mg, 88%): chiral GC [method
isothermal 145 °C/flow = 0.8 mL/min, tR 20.6 (97.4), 21.1 (2.6)] 95%
22
1
(S)-N-[1-(2-Fluoro-4-methoxyphenyl)ethyl]-acetamide (5j).29
White solid (258 mg, 81%): mp 86−87 °C; chiral GC [method
isothermal 13 0 °C/flow = 0.8 mL/min, tR 44.65 min (96.5%), 45.92
ee; [α]D = −104 (c 0.28, CHCl3); H NMR (400 MHz, CDCl3) δ
1.50 (d, J = 6.8 Hz, J = 7.2 Hz, 3H), 2.08 (s, 3H), 3.84 (s, 3H), 5.12
(m, J = 7.2 Hz, 1H), 6.0 (s, 1H), 6.83 (m, 1H), 6.93 (d, J = 8 Hz, 1H),
7.29 (t, J = 8 Hz, 1H); 13C NMR (100 MHz, CDCl3) δ 21.7, 23.4,
48.8, 55.2, 112.3 112.4, 118.4, 129.7, 144.9, 159.8, 169.1; FT-IR (ν,
cm−1) 3253, 3068, 2975, 1643, 1532, 827, 755.
(3.5%)] 93% ee; [α]20 = −106 (c 1.4, CHCl3), Lit.29 [α]D20 = −47.9
D
(c 0.82, EtOH) for the S enantiomer; 1H NMR (400 MHz, CDCl3) δ
1.51 (d, J = 7.2, Hz, 3H), 2.01 (s, 3H), 3.83 (s, 3H), 5.38 (m, 1H),
5.98 (s, 1H), 6.67 (m, 2H), 7.22 (1H, t, J = 8.6 Hz); 13C NMR (100
MHz, CDCl3) δ 21.5, 23.4, 45.3, 55.6, 102.4 (d, J = 25 Hz); 109.7 (d, J
= 3 Hz) 122.2 (d, J = 14 Hz), 128.8 (d, J = 7 Hz), 161 (d, J = 24 Hz)
169.9; HRMS (ESI-TOF) mz [M + Na]+ Calcd for C11H14FNNaO2
234.0901, found 234.0909.
(S)-N-[1-(4-Methylthiophenyl)ethyl] acetamide (5c).27 White
solid (89% yield): mp 104−106 °C chiral GC [isothermal 120 °C/flow
= 0.8 mL/min, 44.7 min (98.9%), tR 45.0 min (1.1%)] 97.8% ee;
22
1
[α]D = −14 (c 1.05, CHCl3); H NMR (400 MHz, CDCl3) δ 1.50
(d, J = 6.8 Hz, 3H), 2.04 (s, 3H), 3.84 (s, 3H), 5.10 (m, J = 7.4 Hz,
1H), 7.26 (m, 4H); 13C NMR (100 MHz, CDCl3) δ 16.0 (CH3), 21.6
(CH3), 23.4 (CH3), 21.6 (CH), 48.3, 126.4; 127.0, 137.4, 140.2.
(S)-1-[(2-Fluorophenyl)ethyl] acetamide (5d).28 White solid
(0.113 g, 62%): mp 126−128 °C; chiral GC [method isothermal 120
°C/flow = 0.80 mL/min, tR 29.85 min (94.3%). 30.14 min (5.7%)]
88% ee; 1H NMR (400 Hz, CDCl3) δ 1.53 (d, J = 7.2 Hz, 3H), 2.02 (d,
3H, J = 20 Hz), 5.31 (q, J = 7.2 Hz, 1H), 7.10 (m, 1H), 7.15 (1H, m),
7.28 (2H, m); 13C NMR (CDCl3, 100 Hz) δ 21.5, 23.4, 45.7, 116.0 (d,
J = 22 Hz), 124.4, 128.3 (d, J = 9 Hz), 130.9 (d, J = 14 Hz), 162.0 (d, J
= 244 Hz), 169.1; GC−MS (tR 11.82 min) m/z 181.1, 166.2, 124.1,
122.1, 103.1, 97.1; FT-IR (ν, cm−1) 3253, 3069, 2974, 1650 (CO),
1553, 1375, 1228.
(S)-N-[1-(Naphthalene-1-yl)ethyl] acetamide (5k).25 White
solid (0.165 g, 77%): mp 136−138 °C; HPLC [column CHIRALCEL
OD-H, 70:30 hexanes/isopropanol, flow 1.0 mL/min, tR 4.2 min
1
(4.5%), 7.1 min (95.5%)] 91% ee; [α]20 = +49 (c 1.00, CHCl3); H
D
NMR (CDCl3, 400 MHz) δ 1.67 (t, J = 7.2 Hz, 3H), 1.97 (s, 3H), 5.73
(s, 1H), 5.99 (t, J = 7.1 Hz, 1H), 7.59 (m, 4H), 7.87 (d, J = 8 Hz, 1H),
7.91 (d, J = 7.6 Hz, 1H), 8.17 (d, J = 8.36 Hz, 1H); 13CNMR (CDCl3,
100 MHz) δ 20.7, 23.4, 44.7, 122.6, 123.5, 125.2, 125.9, 126.7, 128.5,
128.8, 131.2, 133.9, 138.2, 168.9; GC−MS (tR 17.89 min) m/z 213.2,
198.2, 170.2, 156.2, 129.2, 128.2, 127.2; FT-IR (υ, cm−1) 3293, 3051,
2970, 1627, 1537, 1369, 1259.
General Procedure for the Asymmetric Reduction of (Z)-
Benzyl Oximes with Spiroborate 1 as Catalyst.8a To an oven-
dried 25 mL two-necked flask charged with a magnetic stirrer and
(S)-1-[(4-Fluorophenyl)-ethyl] acetamide (5e).29 Clear white
oil (236 mg, 87%): chiral GC [method isothermal 120 °C/flow = 0.8
I
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under N2 was added catalyst 1 (0.15 equiv) and dry THF (10 mL). A
solution of BH3−THF (1 M in THF) (4 equiv) was added in one
portion. The resulting mixture was stirred at 25 °C for 30 min or until
complete dissolution was observed. Hydrogen gas was liberated during
the process. After the solution was cooled at 0 °C, a solution of
benzyloxime (1 equiv) in 5 mL of THF was added at a slow rate via a
syringe pump. The resulting mixture was stirred at 0 °C for 48−72 h,
or until conversion was completed as determined by TLC. The
reaction was slowly quenched with 6 N HCl and then treated with 6 N
NaOH until the solution was basic. It was extracted with ether, and the
combined organic phases were washed with saturated aqueous NaCl
solution and dried over anhydrous Na2SO4. The solvent was removed
under a vacuum, and the residue was analyzed by GC and used directly
to prepare the stable acetamide derivatives.
(R)-N-[1-(3-Bromophenyl)ethyl] acetamide (8g).36 Light yel-
low liquid (0.7 g, 79%): [α]22D = +94 (c 4.3, CHCl3)), Lit.36 [α]21
=
D
+46.7 (c 1.05, CHCl3); chiral GC [gradient method start at 80 °C,
increase 5 °C/min up to 150 °C, hold for 20 min, increase 5 °C/min
up to 170 °C, hold for 40 min, increase 5 °C up to 195 °C and hold
1
for 20 min, tR 24.67 min (3.5%), 25.56 (96.5%)] 93% ee H NMR
(CDCl3) δ 1.44−1.45 (d, J = 6.8 Hz, 3H), 1.98 (s, 3H), 5.05−5.08 (m,
1H), 5.93 (br, 1H), 7.16−7.26 (m, 2H), 7.36−7.39 (m, 2H); 13C
NMR (CDCl3) δ 21.9, 23.5, 48.5, 122.9, 125.2, 129.3, 130.4, 130.6,
145.9, 169.4.
(R)-N-[1-(4-Nitrophenyl)ethyl] acetamide (8h).37 White solid
(0.87 g, 71%): mp 131−134 °C; [α]22D = +115 (c 0.8, CHCl3); Lit.37
[α]22 = +146.7 (c 2.97, EtOH); chiral GC [gradient method start at
D
80 °C, increase 5 °C/min up to 150 °C, hold for 20 min, increase 5
(R)-N-[1-(Phenyl)ethyl] acetamide (8a)..25,33 White solid (0.062
°C/min up to 170 °C, hold for 40 min, increase 5 °C up to 195 °C
g, 76%): mp 88−91 °C, Lit.33 89−91 °C; [α]22 = +114 (c 1.1,
1
and hold for 20 min, tR 52.79 min (10%), 54.45 (90%)] 80% ee; H
D
CHCl3), Lit.33 [α]20 = +131 (c 1.0, CHCl3); chiral GC [method
NMR (CDCl3) δ 1.496−1.513 (d, J = 6.8 Hz, 3H), 2.02 (s, 3H),
5.15−5.19 (m, 1H), 5.73 (br, 1H), 7.45−7.48 (m, 2H), 8.17−8.21 (m,
2H); 13C NMR (CDCl3) δ 22.0, 23.5, 48.8, 124.1, 127.1, 151.0, 169.5.
(R)-N-[1-(Naphthalen-1-yl)ethyl]acetamide24,25 (8i). White
solid (0.287 g, 79%): mp 148−151 °C, Lit.24 153 °C, (S isomer),
Lit.25 147−149 °C; chiral GC [gradient method start at 80 °C,
increase 5 °C/min up to 150 °C, hold for 20 min, increase 5 °C/min
up to 170 °C, hold for 40 min, increase 5 °C up to 195 °C and hold
D
isothermal 120 °C/flow = 0.8 mL/min, 42.40 min, tR (1.3%), 46.37
min (98.7%)] 97% ee; 1H NMR (CDCl3) δ 1.46−1.48 (d, J = 7.2 Hz),
1.97 (s, 3H), 5.08−5.15 (m, 1H), 5.92 (br, 1H), 7.23−7.35 (m, 5H);
13C NMR (CDCl3) δ 21.4, 23.1, 48.6, 125.2, 126.0, 127.1, 128.4, 142.9,
169.1.
(R)-N-[1-(p-Tolyl)ethyl] acetamide (8b).34 White solid (61.5 mg,
74%): mp 85−86 °C, Lit.34 80−81 °C; [α]22D = +140 (c 0.5, CHCl3),
Lit.34 +146 (c 0.5, CHCl3); chiral GC [gradient method 70 °C for 30
min, then 1 °C/1 min up to 190 °C, then 40 min, tR 28.24 min (4.0%),
for 20 min, tR 45.59 min (100%), 44.9 min (0%)] >99% ee [α]22
=
D
+36 (c 0.8, CHCl3), Lit.24 [α]20D = −47.9 (c 0.82, EtOH, (S isomer,
78% ee); 1H NMR (CDCl3) δ 1.66−1.67 (d, J = 6.8 Hz), 1.96 (s, 3H),
5.65 (br, 1H), 5.91−5.95 (m, 1H), 7.43−7.56 (m, 4H), 7.79−7.87 (m,
2H), 8.09−8.11 (m, 1H); 13C NMR (CDCl3) δ 20.8, 23.6, 44.8, 122.8,
123.7, 125.4, 126.1, 128.6, 129.0, 131.3, 134.1, 138.4, 169.0.
1
28.6 7 (96.0%)] 92% ee; H NMR (CDCl3) δ 1.45−1.47 (d, J = 6.8
Hz, 3H), 1.95 (s, 3H), 2.32 (s, 3H), 5.06−5.11 (m, 1H), 5.67 (br,
1H), 7.13−7.25 (m, 4H); 13C NMR (CDCl3) δ 20.8, 21.4, 23.3, 48.3,
125.1, 125.9, 129.1, 136.9, 139.9, 168.8.
(R)-N-[1-(4-Methoxylphenyl)ethyl] acetamide (8c).34 White
solid (0.067 g, 90%): mp 83−85 °C, Lit.34 82−83 °C]; [α]22D = +140
(c 0.3, CHCl3), Lit.34 [α]20 = +145 (c 1.0, CHCl3); chiral GC
[gradient method start at 80 °DC, increase 5 °C/min up to 150 °C, hold
for 20 min, increase 5 °C/min up to 170 °C, hold for 40 min, increase
5 °C up to 195 °C and hold for 20 min, tR 28.13 min (4.4%), 29.20
(95.6%)] 91% ee; 1H NMR (CDCl3) δ 1.61−1.63 (d, J = 6.8 Hz, 3H),
3.78 (s, 3H), 4.30−4.32 (m, 1H), 6.86−6.88 (m, 2H), 7.38−7.40 (m,
2H), 8.30 (br, 1H); 13C NMR (CDCl3) δ 20.6, 51.2, 55.2, 114.3,
128.1, 129.9, 159.8.
Typical Procedure for the Synthesis of Class I Calcimimetics
Analogues: (R)-3-(2-Chlorophenyl)-N-(1-naphthalen-1-yl-
ethyl)propionamide (10b). To an oven-dried 50 mL round-
bottomed flask equipped with a magnetic stirring bar and nitrogen
inlet, 3-(2-chlorophenyl)propionic acid (0.188 g, 1 mmol) and
anhydrous CH2Cl2 (4 mL) were added. Dicyclocarbodiimide (DCC)
(0.229 g, 1.1 mmol) and dimethylaminopyridine (DMAP) (12.3 mg,
0.10 equiv) were added, and the solution was stirred for 1 h at 25 °C.
A cloudy mixture was observed. Subsequently, (S)-N-(1-naphthalene-
1-yl)ethyl amine (1.0 mmol, 0.175 g) was added to the solution and
stirred for 30 min. The reaction was monitored by TLC (mobile
phase, hexane/ethyl acetate, 1:1). After the reaction was completed,
the solution was filtered through a Celite pad (60 mL filter, 1.5 cm
height) and washed with CH2Cl2 (50 mL). The solvent was removed
under a vacuum using the rotoevaporator and purified by column
chromatography using silica (100−400 mesh, 60 Å, 21 g, 2 cm
diameter) and a mobile phase composed of CH3Cl/MeOH (1600:9 v/
v) to obtain a white solid (0.335 g, 99%): mp 126−127 °C; chiral
HPLC [column CHIRALCEL OD-H), flow rate 0.8 mL/min, MeOH
80%, hexane 20%, tR 4.85 min (50.69%) 5.39 min (49.31%)] >99% ee;
[α]22D = +26 (c 2.67, CHCl3); 1H NMR (400 MHz, CDCl3) δ 1.65 (d,
J = 6.8 Hz), 2.52 (t, J = 7.6 Hz), 3.14 (td, J = 8.0 Hz, J2 = 2.2 Hz, 2H),
5.66 (d, J = 8.0 Hz, 1H, NH), 5.96 (m J = 7.4 Hz, 1H), 7.15 (m, 2H),
7.25 (m, 1H), 7.46 (m, 2H), 7.57 (dd, J = 6.6 Hz, J = 2.2 Hz, 1H), 7.90
(dd, J = 6.6 Hz, J = 2.2 Hz, 1H), 8.11(d, J = 8.4 Hz, 1H); 13C NMR
(100 MHz, CDCl3) δ 23.7, 30.4, 31.4, 53.7, 122.8, 123.0, 125.3, 125.8,
126.7, 127.2, 127.3, 129.0, 129.5, 130.4, 131.4, 133.9, 134.0, 139.8,
141.4. FT-IR (v, cm−1) 3287.59 (NH), 3055, 2928, 1698, 1631, 1538,
778, 757; HRMS (ESI-TOF) m/z [M + H]+ Calcd for C21H21ClNO
338.1306, found 338.1317.
(R)-N-[1-(3-Methoxyphenyl)ethyl] acetamide (8d).35 Oily
liquid (0.164 g, 75%): [α]22 = +87 (c 3.4, CH3OH), Lit.35 [α]20
D
D
= +166.13 (c 1.0, CH3OH)]; chiral GC [gradient method start at 80
°C, increase 5 °C/min up to 150 °C, hold for 20 min, increase 5 °C/
min up to 170 °C, hold for 40 min, increase 5 °C up to 195 °C and
1
hold for 20 min, tR 28.78 min (3.5%), 30.16 (96.5%)] 93% ee; H
NMR (CDCl3) δ 1.45−1.47 (d, J = 6.8 Hz, 3H), 1.97 (s, 3H), 3.79 (s,
3H), 5.06−5.09 (m, 1H), 5.95 (br, 1H), 6.77−6.90 (m, 3H), 7.22−
7.26 (m, 1H); 13C NMR (CDCl3) δ 21.9, 23.5, 49.0, 55.4, 112.4,
112.6, 118.6, 129.9, 145.1, 160.0, 169.4.
(R)-N-[1-(4-Chlorophenyl)ethyl] acetamide (8e).25 White solid
(0.134 g, 69%): mp 96−98 °C, Lit.25 97−99 °C; [α]22D = +126 (c 1.0,
CHCl3), Lit.25 [α]20 = +122.3 (c 1.38, EtOH); chiral GC [gradient
method start at 80 °DC, increase 5 °C/min up to 150 °C, hold for 20
min, increase 5 °C/min up to 170 °C, hold for 40 min, increase 5 °C
up to 195 °C and hold for 20 min, tR 25.04 min (3.9%), 26.07
(96.1%)] 92% ee ; 1H NMR (CDCl3) δ 1.45−1.47 (d, J = 6.8 Hz, 3H),
1.98 (s, 3H), 5.07−5.11 (m, 1H), 5.64 (br, 1H), 7.23−7.34 (m, 4H);
13C NMR (CDCl3) δ 21.5, 23.2, 48.0, 127.1, 127.4, 128.5, 138.6, 132.9,
141.5.
(R)-N-[1-(4-Bromophenyl)ethyl]acetamide (8f).36 White solid
(R)-3-(2-Chlorophenyl)-N-1-(naphthalene-1-yl)-propan-1-
amine (11b)..5l,m To an oven-dried 50 mL round-bottom flask
equipped with condenser, a magnetic stirring bar and a nitrogen inlet,
(S)-3-(2-chloro-phenyl)-N-(1-naphthalen-1-yl-ethyl)propionamide
(10b) (0.606 g, 1.87 mmol) and anhydrous THF (1.82 mL) were
added. Then, BH3−THF (2.02 mL, 1 M, 2 mmol) was added, and the
reaction mixture was refluxed overnight. After the mixture was allowed
to cool at room temperature, methanol (5 mL) was slowly added. The
mixture was heated to reflux, left to cool at room temperature and
concentrated under a vacuum The residue was washed with water (15
(0.17 g, 73%): mp 133−135 °C, Lit.36 101.5−103.2 °C; [α]22D = +80
(c 1.6, CHCl3, Lit.36 [α]21 = +72.2 (c 1.02, CHCl3); chiral GC
D
[gradient method start at 80 °C, increase 5 °C/min up to 150 °C, hold
for 20 min, increase 5 °C/min up to 170 °C, hold for 40 min, increase
5 °C up to 195 °C and hold for 20 min, tR 34.16 min (3.7%), 35.57
(96.3%)] 92% ee; 1H NMR (CDCl3) δ 1.45−1.47 (d, J = 6.8 Hz), 1.98
(s, 3H), 5.06−5.09 (m, 1H), 5.71 (br, 1H), 7.17−7.19 (m, 2H), 7.44−
7.46 (m, 2H); 13C NMR (CDCl3) δ 21.7, 23.5, 48.3, 121.2, 128.0,
131.8.
J
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Article
mL) and extracted with diethyl ether (15 mL × 3). The organic phase
was collected and dried over potassium carbonate. After filtration and
solvent removal under a vacuum, the oily product was purified by
(d, J = 8.0 Hz, 1H); 13C NMR (100 MHz, CDCl3) δ 23.7, 32.1, 33.7,
47.6, 53.7, 122.7, 123.0, 125.3, 125.7, 127.1, 128.3, 128.4, 129.0, 131.4,
134.0, 141.4, 142.2.
column chromatography using hexane/ethyl acetate (8:2) to afford a
Typical Procedures for Synthesis of Class II Calcimimetics
Analogues. 1-(3-Bromopropoxy)-2-chlorobenzene.39 To a
round-bottomed flask equipped with a magnetic stirring bar were
added sodium hydride (43.2 g, 1.8 mmol) and anhydrous DMF (5
mL). The reaction mixture was cooled at 0 °C, and 2-chlorophenol
(257 mg, 2.0 mmol) was added using a syringe. The reaction mixture
was stirred for 1.5 h at 0 °C, and 1,3-dibromopropane (606 μL, 6.0
mmol) was added dropwise. The mixture was stirred at 25 °C
overnight. The reaction was quenched with an aqueous solution of
NH4Cl (10 mL) and extracted with ether (3 × 15 mL). The organic
phase was dried over Na2SO4, filtered and concentrated to obtain 287
mg of clear oil that was purified by gradient column chromatography
over silica gel (silica 8.0 g, 1.0 mm diam., 13 mm long), starting with
hexane then with hexane/ethyl acetate (15:1) to obtain a clear oil (267
1
clear oil (0.12 g, 70%): [α]22 = +27 (c 2.5, CHCl3); H NMR (400
D
MHz, CDCl3) δ 1.56 (d, J = 6.4 Hz), 1.89 (t, J = 7.6 Hz), 2.71 (m,
2H), 2.83 (m, 4H), 4.71 (quart, J = 6.4 Hz, 1H), 7.18 (m, 3H), 7.38
(m, 1H), 7.54 (m, 3H), 7.73 (d, J = 6.8 Hz, 1H), 7.81 (d, J = 8.4 Hz,
1H), 7.94 (d, J = 8.4 Hz, 1H, 8.27 (d, J = 8.4 Hz, 1H); 13C NMR (100
MHz, CDCl3) δ 20.7, 29.6, 36.3, 44.6, 122.5, 123.4, 125.2, 125.8,
126.5, 126.9, 127.0, 127.8, 127.9, 128.3, 128.7, 129.4, 129.6, 130.8,
131.1, 133.7, 133.9, 138.2, 138.2, 170.6; FT-IR (v, cm−1) 3060, 2925,
2859, 1595, 1571, 799, 679.
(R)-3-(2-Chlorophenyl)-N-1-(naphthalene-1-yl)propan-1-
amine hydrochloride salt. To a stirred solution of (R)-3-(2-
chlorophenyl)-N-1-(naphthalene-1-yl)propan-1-amine (0.124 mg, 0.38
mmol, 1.0 equiv) in dichloromethane (3 mL) at room temperature
was added dropwise a solution of chlorotrimethylsilane (0.050 mL,
1.14 mmol, 3.0 equiv) in methanol (0.015 mL, 1.14 mmol, 3.0 equiv).
The reaction was stirred overnight at room temperature, and the
solvent was removed under reduced pressure. The product was washed
with diethyl ether obtaining white crystals (54 mg, 44%): mp 193−195
1
mg, 46%): H NMR (400 MH, CDCl3) δ 2.42 (m, J = 10 Hz, 2H),
3.72 (t, J = 6.4 Hz, 2H), 4.24 (t, J = 6.0 Hz, 2H,), 6.98 (m, 2H), 7.28
(m, 1H,), 7.27 (m, 1H); 13C NMR (100 MHz, CDCl3) 30.0, 32.3,
66.4, 113.6, 121.7, 123.1, 127.7, 130.3, 154.2; GC−MS (tR 13.28 min,
80%) m/z 250, 248.1, 128.1, 102.1; (tR 19.97 min, 20%) m/z 296.1,
169.1, 168.2, 141.1.
1
°C; H NMR (400 MHz, CDCl3, ppm) δ 2.06 (d, J = 6.8 Hz, 3H),
2-(3-Bromopropoxy)-1,3-dimethyl-benzene.40 The crude
product was purified by preparative TLC using hexane/ethyl acetate
(30:1) as mobile phase obtaining a clear oil (488 mg, 58%): GC−MS
(tR 8.42 min, 21%) m/z 162.1, 147.2, 91.2, 72.2; (tR 12.91 min, 73%)
242.1, 122.2, 107.3, 91.2; 1H NMR (400 MHz, CDCl3) δ 2.36 (s, 6H),
2.40 (m, 2H), 3.76 (t, J = 6.6 Hz, 2H), 3.95 (d, J = 5.8 Hz, 2H), 6.98−
7.08 (m, 3H); 13C NMR (100 MHz, CDCl3) δ 16.2, 30.3, 33.5, 69.0,
123.9, 128.8, 130.9, 155.5; FT-IR (ν, cm−1) 2873, 1479, 1262.
1-(3-Bromopropoxy)-3-(trifluoromethyl)benzene.41 The
product was purified by preparative TLC (20 × 20 cm, 1500 μm)
using hexane/ethyl acetate (20:1) as mobile phase to give a clear oil
2.33 (t, J = 7.8 Hz), 2.63 (m, 2H), 2.83 (s, 2H), 5.25 (s, 1H), 7.10 (m,
2H), 7.21 (m, 1H), 7.63 (m, 3H), 7.97 (m, 3H), 8.29 (d, J = 6.8 Hz,
1H, 10.09 (s, 1H), 10.65 (s, 1H); 13C NMR (100 MHz, CDCl3) δ
21.4, 25.7, 30.3, 45.4, 53.3, 121.3, 125.1, 126.1, 126.2, 126.8, 127.3,
127.7, 129.4, 129.4, 130.1, 130.7, 132.2, 133.7, 133.8, 137.4; FT-IR (v,
cm−1) 2963.0, 2711, 1588, 756−681.
(R)-N-(1-Naphthalen-1-yl-ethyl)-3-phenyl-propionamide
(10a).38a To an oven-dried 25 mL round-bottom flask equipped with
a magnetic stirring bar and nitrogen inlet were added 3-propionic acid
(0.98 g, 0.65 mmol) and anhydrous CH2Cl2 (8 mL). Dicyclocarbo-
diimide (DCC) (0.148 g, 0.71 mmol) and dimethylaminopyridine
(DMAP) (8 mg, 0.06 mmol) were added, and the solution was stirred
for 1 h at 25 °C. Then, (S)-N-(1-naphthalene-1-yl)ethyl amine (112
mg, 0.65 mmol) was added, and the reaction mixture was stirred for
additional 30 min. After the solution was filtered through a silica (20
g) and Celite pad (7.3 g) and washed with a mixture of CH2Cl2/
CH3OH (160:0.9), the solvent was removed under a vacuum.
(Naphthalen-1-yl-ethyl)-3-phenyl-propionamide was obtained (179
mg, 91%) as a bone white solid: mp 166−167 °C; HPLC [column
CHIRALCEL OD-H, flow rate 0.8 mL/min, MeOH 40%, Hexane
1
(600 mg, 53%): H NMR (400 MHz, CDCl3,) δ 2.39 (m, J = 6 Hz,
2H), 3.67 (t, J = 6.4 Hz, 2H), 4.20 (m, J = 5.8 Hz, 2H), 7.13 (m, J = 8
Hz, 1H), 7.20 (s, 1H), 7.28 (t, J = 7.6 Hz, 1H), 7.45 (t, J = 8 Hz, 1H);
13C NMR (100 MHz, CDCl3) δ 29.7, 32.2, 65.5, 111.3, 117.6, 117.7,
121.2 (q, J = 271 Hz), 130.0, 131.9 (q, J = 32 Hz), 158.8; FT-IR (ν,
cm−1) 2939, 2882, 1591, 1326, 1237, 1100, 783, 748, 563.
(3-Bromopropylsulfanyl)-benzene.42 The crude mixture was
purified by silica gel column chromatography (35 g, 2.6 cm diam, 14.5
cm long) using hexane. The fractions 19−42 were combined and
60%, tR 4.66 min (100%) 6.45 min (0%)] >99% ee; [α]22 = +35 (c
D
1
concentrated to obtain a clear oil (503 mg, 71%): H NMR (400
1
2.67, CHCl3); H NMR (100 MHz, CDCl3) δ 1.64 (d, J = 6.8 Hz,
MHz, CDCl3) δ 2.20 (m, 2H), 3.12 (t, J = 6.8 Hz, 2H), 3.58 (t, J = 6.4
Hz, 2H); 13C NMR (100 MHz, CDCl3) δ 31.8, 32.0, 126.3, 129.0,
129.6, 135.6; FT-IR (ν, cm−1) 1479, 710; GC−MS (tR, 13.12 min) m/
z 232.0, 151.1, 123.1, 110.2.
3H), 2.50 (t, J = 7.4 Hz, 2H), 3.02 (m, 2H), 2.59 (d, J = 7.6 Hz, 2H),
5.95 (t, J = 7.4 Hz, 1H), 7.19−7.31 (m, 5H), 7.42−7.52 (m, 2H),
7.52−7.54 (m, 2H), 7.83 (d, J = 7.6 Hz, 1H), 7.92 (d, J = 7.2 Hz, 1H),
8.11 (d, J = 7.6 Hz, 1H); 13C NMR (100 MHz, CDCl3) δ 20.6, 31.7,
38.5, 44.6, 122.5, 123.4, 125.19, 125.8, 126.2, 126.6, 128.3, 128.4 128.5,
128.7, 131.1, 133.9, 138.1, 140.7, 170.1.
1-(3-Bromopropylsulfanyl)-4-methyl-benzene.43 The product
was purified by preparative TLC using hexane/ethyl acetate (65:1) as
mobile phase to give a yellow oil (613 mg, 63%): 1H NMR (400 MHz,
CDCl3) δ 2.17 (m J = 6.6 Hz, 2H), 2.38 (s, 3H), 3.07 (t, J = 6.6 Hz),
3.57 (t, J = 6.4 Hz, 2H). 7.16 (d, J = 4.4 Hz, 2H), 7.32 (d, J = 4.4 Hz,
2H); 13C NMR (100 MHz, CDCl3) δ 21.7, 31.9, 32.0, 33.2, 129.8
130.5, 131.7, 136.6; FT-IR (ν, cm−1) 2921.4, 1600, 1492, 1433.
(R)-N-[3-(2-Chlorophenoxy)-propyl]-N-(1-naphthalen-1-yl-
ethyl)-amine (13a). The product was purified by preparative TLC
using hexane/ethyl acetate (6:1), obtaining a yellow oil (131 mg,
56%): HPLC of N-acetyl derivative [chiral column CHIRALPAK AD-
(R)-N-(1-Naphthalen-1-yl-ethyl)-3-phenyl-propionamide
(10a).38a White solid (179 mg, 91%): mp 166−167 °C; HPLC
[column CHIRALCEL OD-H, flow rate 0.8 mL/min, MeOH 40%,
Hexane 60%, tR 4.66 min (100%) 6.45 min (0%)] >99% ee; [α]22
=
D
+35 (c 2.67, CHCl3); 1H NMR (100 MHz, CDCl3) δ 1.64 (d, J = 6.8
Hz, 3H), 2.50 (t, J = 7.4 Hz, 2H), 3.02 (m, 2H), 2.59 (d, J = 7.6 Hz,
2H), 5.95 (t, J = 7.4 Hz, 1H), 7.19−7.31 (m, 5H), 7.42−7.52 (m, 2H),
7.52−7.54 (m, 2H), 7.83 (d, J = 7.6 Hz, 1H), 7.92 (d, J = 7.2 Hz, 1H),
8.11 (d, J = 7.6 Hz, 1H); 13C NMR (100 MHz, CDCl3) δ 20.6, 31.7,
38.5, 44.6, 122.5, 123.4, 125.19, 125.8, 126.2, 126.6, 128.3, 128.4 128.5,
128.7, 131.1, 133.9, 138.1, 140.7, 170.1.
H, method 96% hexane:4% isopropanol, flow 1.0 mL/min, 16.4 min
1
(100%), 18.7 min (0%)] >99% ee; [α]20 = +55 (c 1.25, CHCl3); H
D
NMR (CDCl3, 400 MHz) δ 1.57 (d, J = 6.4, 3H,), 2.08 (m, 2H), 2.87
(m, 2H), 4.16 (t, J = 6.0 Hz, 2H), 4.73 (m, 1H), 6.92 (m, 2H), 7.24
(m, 1H), 7.40 (m, 1H), 7.41 (m, 1H), 7.47 (m, 3H), 7.70 (d, J = 7.2
Hz, 1H), 7.78 (d, J = 7.2 Hz, 1H), 7.91 (m, 1H), 8.25 (t, J = 4.8 Hz,
1H); 13C NMR (CDCl3, 100 MHz) δ 23.6, 29.6, 45.1, 53.9, 67.8,
113.2, 121.3, 122.7, 122.9, 123.0, 125.3, 125.7, 127.1, 127.7, 128.9,
130.2, 131.4, 134.6, 141.2, 154.4; HRMS (ESI-TOF) m/z [M + H]+
Calcd for C21H22ClNO 340.1463, found 340.1459.
(R)-[(1-Naphthalen-1-yl-ethyl)-3-phenyl]-propylamine
(11a).38b After filtration and solvent removal under a vacuum, the oily
product was purified by preparative TLC over silica gel using hexane/
ethyl acetate (5:1) and 0.4% of Et3N to afford a clear oil (171 mg,
59%): [α]22D = +35 (c 2.67, CHCl3); 1H NMR (400 MHz, CDCl3) δ
1.56 (d, J = 6.4 Hz, 3H), 2.67−2.79 (m, 4H), 4.70 (quart, J = 6.4 Hz,
1H), 7.23 (m, 3H), 7.33 (t, J = 7.0 Hz, 2H), 7.56 (m, 3H), 7.72 (d, J =
7.2 Hz, 1H), 7.82 (d, J = 8.0 Hz, 1H), 7.94 (d, J = 7.6 Hz, 1H), 8.26
K
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Article
(R)-N-[3-(2-Chlorophenoxy)propyl]-N-(1-naphthalen-1-yl-
0.72 mmol, 30 equiv) and methanol (33 μL, 0.72 mmol, 30 equiv).
After 15 min, the solvent was removed from the precipitate using a
Pasteur pipet, and the crystals were rinsed with cold ether. The solvent
was removed under reduced pressure to give a white solid (79 mg,
ethyl)-amine hydrochloride salt. White crystals (82%): mp 145
1
°C; [α]20 = −7.0 (c 1.0, CHCl3); H NMR (CDCl3, 400 MHz) δ
D
2.12 (d, J = 6.4 Hz), 2.50 (m, 2H), 3.19 (m, 2H), 4.09 (m, 2H), 6.35
(s, 1H), 6.87 (m, 2H), 7.16 (m, 1H), 7.28 (dd, J = 1.4 Hz, 8 Hz, 1H),
7.61 (m, 3H), 7.95 (m, 2H), 8.08 (d, J = 8.4 Hz, 1H), 8.24, (d, J = 7.2
Hz, 1H), 9.88 (s, 1H), 10.76 (s,1H); 13C NMR (CDCl3, 100 MHz) δ
21.3, 25.9, 43.8, 53.7, 66.2, 113.4, 121.4, 121.8, 122.8, 124.9, 126.0,
126.2, 127.3, 129.4, 129.5, 130.1, 130.7, 132.1, 133.9, 153.6; FT-IR (ν,
cm−1, ATR) 2787, 2726, 1589, 1584, 1487, 1278, 1065, 891.
1
81%): mp 115−117 °C; [α]21 = −5.4 (c 1.1, CHCl3); H NMR (400
MHz, CDCl3) δ 2.12 (d, J = 5.4 Hz, 3H), 2.52 (s, 2H), 3.08 (s, 2H),
4.01 (s, 2H), 5.32 (s, 1H), 6.89 (d, J = 8.4 Hz, 2H), 7.17 (d, J = 7.6
Hz, 1H), 7.31 (m, 1H), 7.67−7.69 (m, 3H), 7.95 (dd, J = 8.0 Hz, J =
16 Hz, 2H), 8.06 (d, J = 8.4 Hz, 1H), 8.27 (d, J = 6.4 Hz, 1H), 10.10
(s, 1H), 10.76 (s, 1H); 13C NMR (100 MHz, CDCl3) δ 21.4, 25.9,
43.4, 53.8, 65.2, 111.3, 117.6, 117.6, 121.3, 124.9, 126.1, 126.1, 126.3,
127.4, 129.4, 129.9, 130.3, 132.1, 133.9, 159.1; FT-IR (ν, cm−1)
2708,1588, 1450,1328, 1118, 777, 695.
(R)-(1-Naphthalen-1-yl-ethyl)-(3-phenylsulfanyl-propyl)-
amine (13d). After the typical procedure, the crude product was
purified by preparative TLC using hexane/ethyl acetate (6:1)
obtaining a yellow oil (1.02 g, 61%): HPLC of N-acetyl derivative
[chiral column CHIRALPAK AD-H, method 96% hexane, 4%
(R)-N-[3-(2,6-Dimethyl-phenoxy)propyl]-(1-naphthalen-1-yl-
ethyl)-amine (13b). The crude product was purified by preparative
TLC using hexane:ethyl acetate (6:1) and 0.4% of triethyl amine
obtaining 103 mg as a clear yellow oil (62%): HPLC of N-acetyl
derivatives [chiral column CHIRALCEL OD-H, hexane/isopropyl
alcohol 95:5%, flow 0.7 mL/min, 20.2 min (1.0%), 23.7 min (99.0%)]
98% ee ; [α]20D = +11 (c 5.2, CHCl3); 1H NMR (CDCl3, 400 MHz) δ
1.60 (d, J = 6.8 Hz, 3H), 2.08 (t, J = 6.6 Hz, 2H), 2.31 (s, 6H), 2.89 (d,
J = 6.8 Hz, 2H), 3.89 (m, 2H), 4.74 (q, J = 6.8 Hz, 1H), 6.96 (dd, J =
6.8 Hz, J = 1.2 Hz, 1H), 7.04 (dd, J = 16.8 Hz, J = 6.8 Hz, 2H), 7.56
(m, 3H), 7.54 (d, 1H, J = 6.8 Hz), 7.80 (d, J = 8.4 Hz, 1H), 7.93 (d, J
= 1.6 Hz, 1H), 8.31 (d, J = 1.6 Hz, 1H); 13C NMR (CDCl3, 100 MHz)
δ 16.3, 23.6, 31.1, 45.4, 53.8, 70.8, 122.7, 123.0, 123.7, 125.3, 125.7,
127.2, 128.8, 129.0, 130.9, 131.3, 134.0, 141.2, 156.0; FT-IR (ν, cm−1)
2924, 1474, 1263, 1200, 1129, 776, 734; HRMS (ESI-TOF) m/z [M +
H]+ Calcd for C23H27NO 334.2165, found 334.2172.
isopropyl alcohol, flow 1.0 mL/min, 16.4 min (100%), 18.1 min
1
(0%)] >99% ee; [α]20 = +33 (c 2.3, CHCl3); H NMR (400 MHz,
D
CDCl3) δ 1.56 (d, 3H, J = 6.4 Hz), 1.89 (quint., J = 7.2 Hz, 2H), 2.76
(m, 2H), 3.04 (m, 2H), 4.68 (m, 1H), 7.27 (t, J = 2.0 Hz, 1H), 7.31−
7.39 (m, 4H), 7.56 (m, 3H), 7.71 (d, J = 6.8 Hz, 1H), 7.82 (d, J = 8.0
Hz, 1H), 7.93 (dd, J = 2.0 Hz, J = 7.2 Hz, 1H), 8.25 (d, J = 7.6 Hz,
1H); 13C NMR (100 MHz, CDCl3) δ 23.7, 29.9, 31.6, 46.7, 53.8,
122.7, 123.0, 125.3, 125.7, 125.8, 125.9, 127.2, 128.9, 129.0, 129.2,
131.3, 134.0, 136.6, 141.1; GC−MS (tR 16.19 min) mz 321.2, 206.2,
170.2, 155.2, 141.2; FT-IR (ν, cm−1) 1734, 1438, 1264, 1130, 690;
HRMS (ESI-TOI) m/z [M + H]+ Calcd for C21H23NS 322.1624,
found 322.1631.
(R)-(1-Naphthalen-1-yl-ethyl)-(3-phenylsulfanyl-propyl)-
amine hydrochloride salt. Beige solid (85 mg, 90%): mp 192−194
°C; [α]20D = −29 (c 1.0, CHCl3); 1H NMR (400 MHz, CDCl3) δ 1.73
(s, 3H), 2.29 (s, 2H), 2.95 (s, 4H), 5.24 (s,1H), 7.17 (m, 4H), 7.62
(m, 4H), 7.99 (m, 3H), 8.26 (d, J = 5.6 Hz, 1H), 10.0 (s, 1H), 10.50
(s, 1H); 13C NMR (100 MHz, CDCl3) δ 21.5, 25.5, 31.2, 44.9, 53.9,
121.4, 125.0, 126.1, 126.2, 126.3, 127.3, 128.9, 129.4, 129.5, 129.7,
130.7, 132.1, 133.9, 135.2; FT-IR (ν, cm−1) 2953, 2785, 1585, 1450,
1250, 691.
(R)-3-(2,6-Dimethyl-phenoxy)-propyl]-(1-naphthalen-1-yl-
ethyl)-amine hydrochloride salt. The crude product was obtained
as a white solid (84%, 33 mg): mp 211−213 °C; [α]20D = −6.0 (c 1.2,
CHCl3); 1H NMR (400 MHz, CDCl3) δ 2.02 (s, 6H, CH3), 2.26 (d, J
= 6.4 Hz, 3H, CH3) 2.52 (m, 2H, CH2), 3.16 (s, 2H, CH2), 3.73 (d, J
= 2 Hz, 2H, CH2), 5.36 (s, 1H, CH), 6.9 (m, 2H), 7.15 (m, 1H), 7.65
(m, 3H), 7.96 (d, J = 9 Hz, 2H, CH), 8.10 (d, J = 8.4 Hz, 1H), 8.31,
+
+
(d, J = 8.4 Hz, 1H), 10.1 (s, 1H, NH2 ), 10.74 (s, 1H, NH2 ); 13C
NMR (100 MHz, CDCl3) δ 16.1, 21.2, 27.1, 44.1, 53.5, 68.9, 121.4,
123.9, 125.2, 126.1, 126.2, 127.3, 128.8, 129.5, 129.6, 130.5, 130.8,
132.1, 133.9, 155.2; FT-IR (ν, cm−1) 2962, 2726.3, 1590, 1471, 1260,
1198.
(R)-N-1-(Naphthalen-1-yl-ethyl)-[3-(3-trifluoromethyl-phe-
noxy)-propan]-1-amine (13c). To a stirred solution of (R)-1-
(naphth-1-ylethyl)amine (93 mg, 0.5 mmol, 1.0 equiv), triethyl amine
(84 μL, 0.6 mmol, 1.2 equiv) and dry THF (2 mL) at 25 °C was added
a solution of 1-(3-bromopropoxy)-3-trifluoromethyl benzene (141 mg,
0.82 mmol, 1.0 equiv) in dry THF (2 mL). A small amount (10 mg) of
1,4-(N,N-dimethylamino)pyridine (DMAP) was then added. The
reaction mixture was heated at reflux for 24 h and monitored by TLC.
After the reaction was completed, the solvent was removed under a
vacuum. The reaction mixture was transferred to a separatory funnel
with 10 mL of water and extracted with CH2Cl2 (3 × 10 mL). The
organic phase was washed with brine (10 mL), dried over K2CO3,
filtered and concentrated to obtain 169 mg of yellow oil. The product
was purified by preparative TLC (20 × 20 cm) using hexane/ethyl
acetate (10:1) and 0.4% Et3N as mobile phase to give a clear oil (129
mg, 69%): HPLC (chiral column CHIRALCEL OD-H, method 3%
IPA, 97% hex, flow 0.9 mL/min) of the N-acetyl derivative, tR 26.3 min
(R)-(1-Naphthalen-1-yl-ethyl)-(3-p-tolylsulfanyl-propyl)-
amine (13e).44 The crude product was purified by preparative TLC
(20 × 20 cm, 1500 μm) using hexane/ethyl acetate (5:1). The product
with Rf = 0.32 was recovered, and the sample concentrated to obtain a
brown oil (128 mg, 77%): HPLC of N-acetyl derivative [chiral column
CHIRALCEL OD-H, hexane/IPA (92:8 v/v); flow 0.7 mL/min, 20.1
1
min (100%)] > 99% ee; [α]20 = +17 (c 2.5, CHCl3); H NMR (400
D
MHz, CDCl3) δ 1.56 (d, J = 6.8 Hz, 3H), 1.87 (m, J = 2.8 Hz, 2H),
2.37 (s, 3H), 2.76 (m, 2H), 2.99 (m, 2H), 4.67 (quart, J = 6.8 Hz, 1H),
7.13 (d, J = 8.0 Hz, 2H,), 7.30 (d, J = 4.8 Hz, 2H), 7.56 (m, 3H), 7.70
(d, J = 6.8 Hz, 1H), 7.81 (d, J = 8.0 Hz, 1H), 7.94 (m, 1H), 8.24 (d, J
= 1.2 Hz, 1H); 13C NMR (CDCl3, 100 MHz) δ 21.0, 23.6, 29.9, 39.3,
46.7, 53.7, 122.7, 129.0, 129.7, 130.1, 131.3, 132.7, 134.0, 136.0, 141.1;
FT-IR (ν, cm−1) 3047, 2920, 1595, 1492, 1368, 798.5, 734.
(R)-(1-Naphthalen-1-yl-ethyl)-(3-p-tolylsulfanyl-propyl)-
amine hydrochloride salt. White solid (58 mg, 92%): [α]20
=
D
−17.0 (c 3.0, CHCl3); 1H NMR (400 MHz, CDCl3) δ 2.05 (d, J = 6.8
Hz, 3H), 2.18−2.32 (m, 2H), 2.22 (s, 3H), 2.82−2.89 (m, 2H), 2.91−
2.99 (m, 2H), 5.21 (s, 1H), 6.98 (d, J = 8.4 Hz, 2H,), 7.09 (d, J = 8.4
Hz, 2H), 7.60−7.66 (m, 2H), 7.66−7.71 (m, 1H), 7.94−8.00 (m, 1H),
8.27 (d, J = 7.2 Hz, 1H); 13C NMR (100 MHz CDCl3) δ 21.0, 23.6,
29.9, 39.3, 46.7, 53.7, 122.7, 129.0, 129.7, 130.1, 131.3, 132.7, 134.0,
136.0, 141.1; FT-IR (ν, cm−1) 2780, 1585, 1449, 1235, 1118, 777, 695.
1
(0.4%), 31.1 min (99.6%) 99% ee; [α]21 +24 (c 1.10, CHCl3); H
NMR (400 MHz, CDCl3) δ 1.57 (d, J = 6.4 Hz), 2.03 (m, 2H), 2.83
(m, 2H), 4.12 (t, J = 6.0 Hz, 2H), 4.71 (q, J = 6.53 Hz, 1H), 7.06 (d, J
= 8.2 Hz, 1H), 7.13 (s, 1H), 7.24 (d, J = 7.6 Hz, 1H), 7.41 (t, J = 8 Hz,
1H), 7.51 (m, 1H), 7.69 (d, J = 6.8 Hz, 1H), 7.79 (d, J = 8.0 Hz, 1H),
7.92 (m, 1H), 8.26 (t, 1H); 13C NMR (100 MHz, CDCl3) δ 23.6, 29.9,
44.6, 53.9, 66.5, 111.3, 117.2, 118.0, 122.7, 122.9, 125.3, 125.6, 125.7,
127.2, 129.0, 129.9, 130.3), 131.6, 131.9, 134.0, 141.1; FT-IR (ν,
cm−1) 3356, 3048, 2963, 1595, 1509, 1119, 1023, 860, 798; HRMS
(ESI-TOF) m/z [M + Na]+ Calcd for C22H22F3NNaO 396.1546,
found 396.1546.
ASSOCIATED CONTENT
■
S
* Supporting Information
Optimization conditions for the reduction of (Z)-benzyloximes,
spectral and chromatographic data of starting materials and
enantiopure compounds. This material is available free of
charge via the Internet at http://pubs.acs.org.
(R)-N-1-(Naphthalen-1-yl-ethyl)-[3-(3-trifluoromethylphe-
noxy)-propan]-1-amine hydrochloride salt. To a solution of the
amine (90 mg, 0.24 mmol, 1.0 equiv) in 3 mL of diethyl ether and 1.0
mL of hexane under nitrogen was added dropwise TMSCl (90 μL,
L
dx.doi.org/10.1021/jo400371x | J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Article
Z.; Roethke, T.; Smith, B. R.; Ward, K. W.; Lee, J.; Keenan, R. M.;
Bhatnagar, P. J. Med. Chem. 2009, 52, 3982. (j) Torres, P. J. Renal Nutr.
2006, 253.
(5) For the synthesis of calcimimetics analogues, see: (a) Kessler, A.;
Faure, H.; Petrel, C.; Ruat, M.; Dauban, P. M.; Dodd, R. H. Bioorg.
Med. Chem. Lett. 2004, 14, 3345. (b) Kessler, A.; Faure, H.; Petrel, C.;
AUTHOR INFORMATION
Corresponding Author
*E-mail: margarita.ortiz1@upr.edu.
Notes
■
The authors declare no competing financial interest.
́
Cesario, M.; Ruat, M.; Dauban, P. M.; Dodd, R. H. J. Med. Chem.
2006, 49, 5119. (c) Poon, S. F.; St. Jean, D. J.; Harrington, P. E.;
Henley, C., III; Davis, J.; Morony, S.; Lott, F. D.; Reagan, J. D.; Ying-
Lin, L. J.; Yang, Y.; Fotsch, C. J. Med. Chem. 2009, 52, 6535.
ACKNOWLEDGMENTS
■
The project described was supported by Award Number U54
RR026139 from the National Center for Research Resources,
and the Award Number 8U54MD 007587-03 from the
National Institute on Minority Health and Health Disparities.
Support for undergraduate scholars by the NIH-INBRE, NIH-
RISE, NIH-MARC, and NSF-AMP programs is also gratefully
acknowledged.
́
(d) Fernandez, I.; Valdivia, V.; Khiar, N. J. Org. Chem. 2008, 73, 745.
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