Asymmetric reduction of nitroalkenes with baker's yeast

Article abstract of DOI:10.1016/S0957-4166(01)00029-5

Various α,β-disubstituted and trisubstituted nitroalkenes were chemoselectively reduced with baker's yeast to the corresponding nitroalkanes. Stereoselectivities of the reduction of α,β-disubstituted nitroalkenes were modest to low, and e.e.s up to 52% were obtained. Trisubstituted nitroalkenes could be reduced to the corresponding nitroalkanes with excellent enantioselectivities, moderate diastereoselectivities and in good yield.

Full text of DOI:10.1016/S0957-4166(01)00029-5

TETRAHEDRON:
ASYMMETRY
Pergamon
Tetrahedron: Asymmetry 12 (2001) 309–318
Asymmetric reduction of nitroalkenes with baker’s yeast
Yasushi Kawai,* Yoshikazu Inaba and Norihiro Tokitoh
Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan
Received 21 December 2000; accepted 10 January 2001
Abstract—Various a,b-disubstituted and trisubstituted nitroalkenes were chemoselectively reduced with baker’s yeast to the
corresponding nitroalkanes. Stereoselectivities of the reduction of a,b-disubstituted nitroalkenes were modest to low, and e.e.s up
to 52% were obtained. Trisubstituted nitroalkenes could be reduced to the corresponding nitroalkanes with excellent enantioselec-
tivities, moderate diastereoselectivities and in good yield. © 2001 Elsevier Science Ltd. All rights reserved.
1. Introduction
papers on the reduction of the carbonꢀcarbon double
bond of nitroalkenes.34–39 Herein, we report the novel
stereoselective reduction of trisubstituted nitroalkenes
with baker’s yeast. The baker’s yeast reduction of b,b-
disubstituted nitroalkenes affords (R)-nitroalkanes
enantioselectively,35,36 while a,b-disubstituted nitroalk-
enes are transformed into almost racemic saturated
nitroalkanes in both aqueous37 and organic solvent
systems.38,39
Because the nitro group can be easily transformed into
other functionalities including amine and carbonyl
groups,1 aliphatic nitro compounds are versatile syn-
thetic building blocks. They are considered to be valu-
able intermediates for the preparation of various
biologically active compounds2 such as alkaloids,3,4
steroids,5,6 amino acid derivatives,7–10 enzyme
inhibitors,11 and of interest to us, cobyric acid.12 Con-
siderable efforts have been made to develop synthetic
methods for chiral nitro compounds. For example, the
diastereoselective nitroaldol reaction with chiral alde-
hydes,13 the stereoselective Michael addition reaction of
nitroalkanes or nitroalkenes,14–20 the [4+2] or [3+2]
cycloaddition reaction of nitroalkenes,21,22 and nitro-
olefination reactions using chiral nitroenamines23,24
have been reported. However, the use of chiral auxil-
iaries is necessary in these reactions, and a catalytic
method of chiral induction would be preferable.
The microbial reduction of carbonyl compounds is
known to be a powerful tool for the synthesis of chiral
alcohols.25 In particular, baker’s yeast (Saccharomyces
cerevisiae) is one of the most widely investigated biocat-
alysts because it is inexpensive, versatile and readily
available.26,27 In contrast to the carbonyl reduction,
only a few investigations on the asymmetric reduction
of carbonꢀcarbon double bonds have been reported.
Most reports involve the reduction of olefins conju-
gated with a carbonyl group.28–33 There have been few
Figure 1. Epimerization of ( )-erythro-3-phenyl-2-nitro-
* Corresponding author. Fax: +81-774-38-3209; e-mail: kawai@
scl.kyoto-u.ac.jp
butane under microbial reduction conditions.
0957-4166/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII: S0957-4166(01)00029-5

310
Y. Kawai et al. / Tetrahedron: Asymmetry 12 (2001) 309–318
Scheme 1.
2. Results and discussion
jected to baker’s yeast reduction. We chose the reduc-
tion of (E)-2-nitro-1-phenylpropene 1a and (E)-2-nitro-
1-phenyl-1-butene 1o as typical models. The reduction
of 1a proceeded rapidly giving the corresponding
nitroalkane (S)-2a chemoselectively, but the stereoselec-
tivity was low with an e.e. of 12%. Elongation of the
substituent at the a-position to an ethyl group increased
the stereoselectivity, giving an e.e. of 39%.
In the earlier report, the non-stereoselective reduction
of a,b-disubstituted nitroalkenes with microbes was
attributed to racemization of the product because of
acidity of the a-proton.34 At first, the rate of racemiza-
tion of the product under the same conditions as the
microbial reduction was evaluated by measuring the
epimerization rate at the a-carbon of erythro-3-phenyl-
2-nitrobutane. The results are shown in Fig. 1. The half
life of the epimerization reaction was estimated to be
188 hours under the reaction conditions, which suggests
that the low stereoselectivities observed were not a
result of non-enzymatic racemization of the product,
because the reduction with yeast was completed within
several hours.
In the whole cell reaction, it is frequently observed that
unsatisfactory stereoselectivity is the result of the simul-
taneous action of several enzymes that have opposite
stereochemistry toward the same substrate.40,41 In such
a case, modification of reaction conditions often
changes the stereoselectivity of the reaction. Stereo-
selectivities under various reaction conditions such as
pH of the reaction medium, addition of an additive,
substrate concentration, and reaction temperature were
investigated, and the results are summarized in Table 1.
As shown in Table 1, lowering the pH of the reaction
medium shifted the stereochemistry towards the oppo-
site configuration but the stereoselectivity was low
(entries 2 and 3). The presence of methyl vinyl
Since there remained a possibility that the microbial
reduction of nitroalkenes would proceed with high
stereoselectivity, we studied the details of the stereo-
selectivity of baker’s yeast reduction of various a,b-di-
substituted nitroolefins (Scheme 1). Twenty aromatic
and aliphatic nitroalkenes were synthesized and sub-
Table 1. Baker’s yeast reduction of nitroolefins 1a and 1o under various reaction conditions
Entry
Substrate
Conditionsa
Reaction time (h)
Yieldb (%)
% E.e.
Config.c
1
2
3
4
5
6
7
8
9
1a
1a
1a
1a
1a
1a
1o
1o
1o
1o
1o
–
2
5
6
6
7
1
5
3
1
91
89
7
12
5
5
S
S
R
S
S
S
pH 5.0
pH 4.0
[MVK]d 15 mM
[glucose] 0.84 M
[S] 7.5 mM
–
7
20
17
19
39
41
44
44
52
72
89
58
65
78
62
55
[S] 7.5 mM
[S] 3.8 mM
25°C
10
11
8
23
15°C
a Water 30 mL, dry baker’s yeast 5 g, [S] 15 mM, ethanol 1 mL.
b Isolated yield.
c Ref. 30.
d Methyl vinyl ketone.

Y. Kawai et al. / Tetrahedron: Asymmetry 12 (2001) 309–318
311
Table 2. Baker’s yeast reduction of disubstituted
nitroolefins 1a–t
b, gave the nitroalkanes 2 in e.e.s of 12 and 13%,
respectively. Similarly, (E)- and (Z)-1-phenyl-2-nitro-1-
butenes, 1o and 1p, were transformed into nitroalkane 2
in e.e.s of 39 and 34%, respectively. Aliphatic nitroalke-
nes 1l–n were also reduced to the corresponding
nitroalkanes with low stereoselectivity. In the reduction
of the series of aromatic nitroalkenes 1a–k, the
stereoselectivity of the reduction was influenced by the
phenyl ring substituent. Only the reduction of the para-
methoxyphenyl derivative 1k afforded the nitroalkane
2k in a moderate e.e. of 45% and the other substrates
were reduced with little selectivity. This reaction has
been reported previously and afforded the racemic
product in both aqueous37 and organic solvent sys-
tems.38,39 Placing an ethyl group a to the nitro group
led to increased stereoselectivity, while increasing the
length of the substituent further to a propyl group
retarded the reaction and led to a decrease in the
stereoselectivity.
Substrate
Reaction time (h)
Yield (%)
% E.e.
1a
1b
1c
1d
1e
1f
1g
1h
1i
2
1.5
1.5
3
3
5
3
7
5
3
5
5
2
5
5
4
32
12
9
81
79
52
47
51
65
61
58
72
68
66
63
48
57
58
55
16
23
52
48
12
13
4
2
7
3
2
0
3
9
45
4
10
4
39
34
9
1j
1k
1l
1m
1n
1o
1p
1q
1r
1s
1t
7
40
19
We next applied the microbial reduction to trisubsti-
tuted nitroalkenes (Scheme 2). The results are summa-
rized in Table 3. Substitution at the b-position retards
the reaction. Although diastereoselectivities in the
reduction of the trisubstituted olefins 3 were moderate,
enantioselectivities were satisfactory, 82–98% e.e., giv-
ing 3-aryl-2-nitrobutanes 4 and 5. In contrast to the
reduction of disubstituted nitroalkenes, the stereoselec-
tivity was influenced by the structural difference
between geometrical isomers. The reduction of (Z)-iso-
mer 3a was found to be more enantioselective than that
of the (E)-isomer 3b and a substituent on the phenyl
ring also affected the reactivity and stereoselectivity.
The o-chloro derivative 3c could not be reduced with
this microbe. The reduction of p-chloro derivative 3e
was the most diastereoselective, giving 4 in high e.e. of
94%. The diastereoisomers thus obtained were readily
separable from each other by column chromatography
on silica gel, allowing enantiomerically pure isomers of
4 and 5 to be obtained without difficulty.
24
ketone40,42 (MVK) or glucose as additives slightly
increased the selectivity (entries 4 and 5). The stereo-
selectivity of microbial reduction is often dependent
upon the substrate concentration,43 and reducing the
substrate concentration led again to a slight increase in
selectivity (entries 6, 8 and 9). The stereoselectivity
increased further on lowering the reaction temperature
(entries 10 and 11). Although these results suggest that
many enzymes participate in the reduction of nitroalk-
enes, no considerable changes in stereoselectivity were
observed in all the reactions investigated.
Since modifying the reaction conditions had no marked
effect on the outcome of the reactions, we investigated
the effect of structural variations of the substrate on the
stereoselectivity of the microbial reduction. Various
a,b-disubstituted nitroalkenes 1a–t were prepared and
subjected to reduction with baker’s yeast, and the
results are listed in Table 2. The stereoselectivity was
not influenced by the structural difference between geo-
metrical isomers, i.e. (E)- and (Z)-isomers. The reduc-
tion of (E)- and (Z)-1-phenyl-2-nitropropenes, 1a and
The enantiomeric excesses of the products were deter-
mined as follows. The nitro compounds were reduced
to amines with ammonium formate catalyzed by palla-
dium on carbon,44,45 followed by conversion to their
amides by reaction with (+)-a-methoxy-a-(trifluoro-
Scheme 2.

312
Y. Kawai et al. / Tetrahedron: Asymmetry 12 (2001) 309–318
Table 3. Baker’s yeast reduction of trisubstituted
nitroolefins 3a–e
3. Conclusion
The baker’s yeast reduction of nitroalkenes affords the
corresponding nitroalkanes chemoselectively. The
stereoselectivity of the reduction is strongly influenced
by the substitution pattern of the substrate. The reduc-
tion of a,b-disubstituted nitroalkenes occurs with low
stereoselectivity. The baker’s yeast reduction of trisub-
stituted nitroalkenes proceeds with satisfactory enan-
tioselectivity, while the diastereoselectivity is modest.
The absolute configuration of the products was deter-
mined by single-crystal X-ray analysis using the anoma-
lous dispersion effect.
Substrate
Yielda (%) % D.e. of 4 % E.e. of 4 % E.e. of 5
3a
3b
3c
3d
3e
72
20
19
–
36
43
98
87
–
82
94
97
83
–
81
92
54
Nrb
52
67
a Isolated yield.
b Not reduced.
methyl)-a-phenylacetyl chloride. Enantio- and dia-
stereomeric excesses in the products were determined by
GLC.
4. Experimental
4.1. Instruments
In order to determine the absolute configuration of 4a
by single-crystal X-ray analysis using the anomalous
dispersion effect of a heavy atom, 4a was reduced to an
amine as above, which was recrystallized from ethanol
as hydrochloride salt 6. Full-matrix refinements using
anomalous dispersion factors for all non-hydrogen
atoms of 6 resulted in an R factor of 0.0844 for (2R,3R)
and 0.0945 for the other enantiomorph. Consequently,
the hydrochloride 6 has the (2R,3R)-configuration (Fig.
2). Use of the Flack parameter (−0.01(2)) also con-
firmed this assignment.46 Thus, it is concluded that 4a
and 5a resulting from yeast reduction have (2R,3R)-
and (2S,3R)-configurations, respectively. Since the
reduction of chloro derivatives 4d and 4e catalyzed
by palladium on carbon also gave amine 6, the abso-
lute configurations of 4d,e and 5d,e were determined to
be (2R,3R) and (2S,3R), respectively, by comparing
their retention times of GLC with those obtained as
above.
1H NMR spectra were recorded on a Varian VXR-200
spectrometer in CDCl3 with tetramethylsilane (TMS) as
an internal reference. Gas chromatograms were
recorded on a Shimadzu GC-14B (OV-1701, 25 m and
OV-1, 25 m) gas chromatograph. IR spectra were
recorded on a Japan Spectroscopic FT/IR-5300 spec-
trometer. X-Ray crystallographic studies were made on
a Rigaku AFC7R diffractometer with filtered Cu-Ka
radiation and a rotating anode generator.
4.2. Materials
Organic reagents and solvents were purchased from
Nacalai Tesque Co., Wako Pure Chemical Ind., Ltd.,
Tokyo Kasei Kogyo Co., Ltd., Kanto Chemical Co.,
Inc. and Aldrich Chemical Co. Dry baker’s yeast was
purchased from Oriental Yeast Co. and stored in a
refrigerator.
Figure 2. The ORTEP drawing of 6. One molecule is omitted for clarity.

Y. Kawai et al. / Tetrahedron: Asymmetry 12 (2001) 309–318
313
4.3. General procedure for the preparation of (E)-a,b-
disubstituted nitroalkenes 1
J=8.3 Hz) and 8.07 (1H, s); IR (KBr): 1522 and 1321
cm−1; anal. calcd for C10H11NO2: C, 67.78; H, 6.26; N,
7.90%. Found: C, 67.74; H, 6.24; N, 7.87%.
The aldehyde (20 mmol) and ammonium acetate (20
mmol) were heated to reflux in nitroethane or 1-nitro-
propane (40 mL) overnight. The solvent was removed
and the organic materials were extracted with ethyl
acetate from water. The organic layer was washed with
brine and dried over anhydrous magnesium sulfate.
Evaporation of the solvent gave a crude product. The
purification methods, the isolated yields, and their spec-
tral data are shown below.
4.3.8.
(E)-1-(2%-Methoxyphenyl)-2-nitropropene
1i.
Purified by recrystallization from ethanol; 78% yield;
1
mp 51–52°C; H NMR (CDCl3, TMS): l 2.39 (3H, s),
3.89 (3H, s), 6.93–7.05 (2H, m), 7.28–7.46 (2H, m) and
8.29 (1H, s); IR (KBr): 1512, 1321 and 1248 cm−1; anal.
calcd for C10H11NO3: C, 62.17; H, 5.74; N, 7.25%.
Found: C, 62.35; H, 5.79; N, 7.21%.
4.3.9.
(E)-1-(3%-Methoxyphenyl)-2-nitropropene
1j.
4.3.1. (E)-1-Phenyl-2-nitropropene 1a. Purified by
recrystallization from ethanol; 67% yield; mp 63–64°C;
1H NMR (CDCl3, TMS): l 2.46 (3H, s), 7.45 (5H, s)
and 8.10 (1H, s); IR (KBr): 1518 and 1323 cm−1; anal.
calcd for C9H9NO2: C, 66.25; H, 5.56; N, 8.58%.
Found: C, 66.42; H, 5.52; N, 8.60%.
Purified by recrystallization from ethanol; 49% yield;
1
mp 42–43°C; H NMR (CDCl3, TMS): l 2.45 (3H, s),
3.84 (3H, s), 6.94–7.04 (3H, m), 7.33–7.42 (1H, m) and
8.05 (1H, s); IR (KBr): 1510, 1319 and 1254 cm−1; anal.
calcd for C10H11NO3: C, 62.17; H, 5.74; N, 7.25%.
Found: C, 62.18; H, 5.73; N, 7.29%.
4.3.2.
(E)-1-(2%-Chlorophenyl)-2-nitropropene
1c.
4.3.10. (E)-1-(4%-Methoxyphenyl)-2-nitropropene 1k.
Purified by column chromatography on silica gel with
hexane/ethyl acetate (20/1); 92% yield; 1H NMR
(CDCl3, TMS): l 2.35 (3H, s), 7.32–7.52 (4H, m) and
8.19 (1H, s); IR (neat): 1524 and 1327 cm−1; anal. calcd
for C9H8NO2Cl: C, 54.70; H, 4.08; N, 7.09%. Found:
C, 54.54; H, 4.11; N, 7.07%.
Purified by recrystallization from ethanol; 48% yield;
1
mp 46–47°C; H NMR (CDCl3, TMS): l 2.47 (3H, s),
3.87 (3H, s), 6.98 (2H, d, J=8.8 Hz), 7.43 (2H, d,
J=8.8 Hz) and 8.08 (1H, s); IR (KBr): 1494, 1302 and
1258 cm−1; anal. calcd for C10H11NO3: C, 62.17; H,
5.74; N, 7.25%. Found: C, 62.20; H, 5.84; N, 7.22%.
4.3.3.
(E)-1-(3%-Chlorophenyl)-2-nitropropene
1d.
4.3.11. (E)-1-Cyclohexyl-2-nitropropene 1l. Purified by
column chromatography on silica gel with hexane/ethyl
acetate (20/1); 87% yield; H NMR (CDCl3, TMS): l
1.10–1.41 (5H, m), 1.54–1.83 (5H, m), 2.02–2.35 (4H,
m) and 6.94 (1H, d, J=10.1); IR (neat): 2930, 2855,
1520 and 1331 cm−1; anal. calcd for C9H15NO2: C,
63.88; H, 8.93; N, 8.28%. Found: C, 63.73; H, 8.93; N,
8.34%.
Purified by column chromatography on silica gel with
hexane/ethyl acetate (20/1); 75% yield; 1H NMR
(CDCl3, TMS): l 2.44 (3H, s), 7.28–7.42 (4H, m) and
8.01 (1H, s); IR (neat): 1522 and 1327 cm−1; anal. calcd
for C9H8NO2Cl: C, 54.70; H, 4.08; N, 7.09%. Found:
C, 54.73; H, 4.07; N, 7.13%.
1
4.3.4.
(E)-1-(4%-Chlorophenyl)-2-nitropropene
1e.
Purified by recrystallization from ethanol; 95% yield;
4.3.12. (E)-4-Methyl-2-nitro-2-pentene 1m. Purified by
column chromatography on silica gel with hexane/ethyl
acetate (20/1); 58% yield; H NMR (CDCl3, TMS): l
1.11 (6H, d, J=6.6 Hz), 2.17 (3H, s), 2.47–2.72 (1H, m)
and 6.95 (1H, d, J=10.3 Hz); IR (neat): 1524 and 1333
cm−1; HRMS found: m/z 129.0794; calcd for C6H11NO2
[M]+: 129.0790.
1
mp 84–85°C; H NMR (CDCl3, TMS): l 2.44 (3H, s),
1
7.35–7.47 (4H, m) and 8.04 (1H, s); IR (KBr): 1512 and
1312 cm−1; anal. calcd for C9H8NO2Cl: C, 54.70; H,
4.08; N, 7.09%. Found: C, 54.76; H, 4.09; N, 7.11%.
4.3.5.
(E)-1-(2%-Methylphenyl)-2-nitropropene
1f.
Purified by column chromatography on silica gel with
hexane/ethyl acetate (20/1); 86% yield; 1H NMR
(CDCl3, TMS): l 2.32 (3H, s), 2.34 (3H, s), 7.19–7.36
(4H, m) and 8.17 (1H, s); IR (neat): 1520 and 1327
cm−1; anal. calcd for C10H11NO2: C, 67.78; H, 6.26; N,
7.90%. Found: C, 67.75; H, 6.29; N, 7.91%.
4.3.13. (E)-4,4-Dimethyl-2-nitro-2-pentene 1n. Purified
by column chromatography on silica gel with hexane/
ethyl acetate (20/1); 32% yield; 1H NMR (CDCl3,
TMS): l 1.23 (9H, s), 2.29 (3H, s) and 7.20 (1H, s); IR
(neat): 1524 and 1327 cm−1; anal. calcd for C7H13NO2:
C, 58.72; H, 9.15; N, 9.78%. Found: C, 58.35; H, 9.21;
N, 9.95%.
4.3.6.
(E)-1-(3%-Methylphenyl)-2-nitropropene
1g.
Purified by column chromatography on silica gel with
hexane/ethyl acetate (20/1); 89% yield; 1H NMR
(CDCl3, TMS): l 2.40 (3H, s), 2.45 (3H, s), 7.21–7.39
(4H, m) and 8.06 (1H, s); IR (neat): 1518 and 1323
cm−1; anal. calcd for C10H11NO2: C, 67.78; H, 6.26; N,
7.90%. Found: C, 67.65; H, 6.28; N, 7.89%.
4.3.14. (E)-1-Phenyl-2-nitro-1-butene 1o. Purified by
column chromatography on silica gel with hexane/ethyl
acetate (20/1); 63% yield; H NMR (CDCl3, TMS): l
1.28 (3H, t, J=7.4 Hz), 2.86 (2H, q, J=7.4 Hz), 7.44
(5H, s) and 8.02 (1H, s); IR (neat): 1520 and 1331 cm−1;
anal. calcd for C10H11NO2: C, 67.78; H, 6.26; N, 7.90%.
Found: C, 67.50; H, 6.23; N, 7.93%.
1
4.3.7.
(E)-1-(4%-Methylphenyl)-2-nitropropene
1h.
Purified by recrystallization from ethanol; 79% yield;
1
mp 53–54°C; H NMR (CDCl3, TMS): l 2.40 (3H, s),
4.3.15. (E)-1-(2%-Methylphenyl)-2-nitro-1-butene 1q.
Purified by recrystallization from ethanol; 76% yield;
2.46 (3H, s), 7.26 (2H, d, J=8.3 Hz), 7.35 (2H, d,

314
Y. Kawai et al. / Tetrahedron: Asymmetry 12 (2001) 309–318
1
mp 41–42°C; H NMR (CDCl3, TMS): l 1.21 (3H, t,
J=7.3 Hz), 2.33 (3H, s), 2.73 (2H, q, J=7.3 Hz),
7.19–7.37 (4H, m) and 8.09 (1H, s); IR (KBr): 1518 and
1327 cm−1; anal. calcd for C11H13NO2: C, 69.09; H,
6.85; N, 7.33%. Found: C, 69.03; H, 6.87; N, 7.34%.
4.5. General procedure for the preparation of 2-aryl-2-
butenes
To a stirred suspension of ethyltriphenylphosphonium
bromide (50 mmol) in dry diethyl ether (200 mL) was
added a solution of butyl lithium in hexane (34 mL,
1.59 mM) at room temperature under an argon atmo-
sphere. After 4 h, the acetophenone or its derivative (52
mmol) was added, and the mixture was stirred under
reflux overnight. The mixture was filtered, and the
filtrate was washed with water and dried over anhy-
drous magnesium sulfate. Evaporation of the solvent
gave a crude product, which was purified by column
chromatography on silica gel with hexane. The isolated
yields and their spectral data are shown below.
4.3.16. (E)-1-(3%-Methylphenyl)-2-nitro-1-butene 1r.
Purified by column chromatography on silica gel with
hexane/ethyl acetate (20/1); 72% yield; 1H NMR
(CDCl3, TMS): l 1.28 (3H, t, J=7.4 Hz), 2.40 (3H, s),
2.86 (2H, q, J=7.4 Hz), 7.21–7.39 (4H, m) and 7.99
(1H, s); IR (neat): 1518 and 1331 cm−1; anal. calcd for
C11H13NO2: C, 69.09; H, 6.85; N, 7.33%. Found: C,
69.07; H, 6.94; N, 7.36%.
4.3.17. (E)-1-(4%-Methylphenyl)-2-nitro-1-butene 1s.
1
4.5.1. 2-Phenyl-2-butene. 62% yield; H NMR (CDCl3,
Purified by column chromatography on silica gel with
1
TMS): l 1.59 (3H, dq, J=6.9, 1.5 Hz), 1.79 (3H, dq,
J=6.8, 1.0 Hz), 2.01–2.04 (3H, 3H, m), 5.56 (1H, qq,
J=6.9, 1.4 Hz), 5.86 (1H, qq, J=6.8, 1.3 Hz) and
7.16–7.39 (5H, 5H, m); IR (neat): 3023, 1495, 1441, 754
and 698 cm−1; anal. calcd for C10H12: C, 90.85; H,
9.15%. Found: C, 90.66; H, 9.24%.
hexane/ethyl acetate (20/1); 89% yield; mp 32–33°C; H
NMR (CDCl3, TMS): l 1.27 (3H, t, J=7.4 Hz), 2.40
(3H, s), 2.87 (2H, q, J=7.4 Hz), 7.33 (2H, d, J=8.3
Hz), 7.33 (2H, d, J=8.3 Hz) and 8.00 (1H, s); IR
(KBr): 1503 and 1316 cm−1; anal. calcd for C11H13NO2:
C, 69.09; H, 6.85; N, 7.33%. Found: C, 69.19; H, 6.78;
N, 7.29%.
1
4.5.2. 2-(2%-Chlorophenyl)-2-butene. 56% yield; H NMR
(CDCl3, TMS): l 1.40 (3H, dq, J=6.8, 1.6 Hz), 1.77
(3H, dq, J=6.8, 1.1 Hz), 1.96–1.99 (3H, 3H, m), 5.48
(1H, qq, J=6.8, 1.5 Hz), 5.62 (1H, qq, J=6.8, 1.5 Hz)
and 7.08–7.41 (5H, 5H, m); IR (neat): 3056, 3030, 1472,
1431, 1047, 1034 and 754 cm−1; anal. calcd for
C10H11Cl: C, 72.07; H, 6.65%. Found: C, 71.91; H,
6.65%.
4.4. General procedure for the preparation of (Z)-a,b-
disubstituted nitroalkenes 1
Nitroethane or 1-nitropropane (20 mmol) was added to
benzaldehyde (20 mmol) at 0°C and stirred for 5 min.
Chromatographic alumina (Merck, activity I) was
added to the mixture and stirred for 1 h at room
temperature. After standing for 23 h, the alumina was
washed with dichloromethane. The filtered extract was
evaporated at reduced pressure to give crude 2-
nitroalkanol, which was used without further
purification.
1
4.5.3. 2-(3%-Chlorophenyl)-2-butene. 56% yield; H NMR
(CDCl3, TMS): l 1.58 (3H, dq, J=7.0, 1.6 Hz), 1.79
(3H, dq, J=6.9, 1.1 Hz), 1.98–2.01 (3H, 3H, m), 5.58
(1H, qq, J=6.9, 1.5 Hz), 5.88 (1H, qq, J=6.9, 1.4 Hz)
and 7.04–7.35 (5H, 5H, m); IR (neat): 3056, 3030, 1593,
1562, 1080, 997 and 781 cm−1; anal. calcd for C10H11Cl:
C, 72.07; H, 6.65%. Found: C, 71.94; H, 6.57%.
Copper(I) chloride (0.20 g) and 1,3-dicyclohexylcar-
bodiimide (20 mmol) were added to a solution of
2-nitroalkanol in diethyl ether (10 mL) at room temper-
ature under an atmosphere of argon for 48 h. The
mixture was filtered and the filtrate was evaporated at
reduced pressure to give a crude mixture of (E)- and
(Z)-isomers of nitroalkene. The purification methods,
the isolated yields and their spectral data are shown
below.
1
4.5.4. 2-(4%-Chlorophenyl)-2-butene. 52% yield; H NMR
(CDCl3, TMS): l 1.58 (3H, dq, J=7.0, 1.5 Hz), 1.79
(3H, dq, J=6.9, 1.1 Hz), 1.98–2.01 (3H, 3H, m), 5.57
(1H, qq, J=7.0, 1.5 Hz), 5.85 (1H, qq, J=6.9, 1.4 Hz)
and 7.10–7.33 (5H, 5H, m); IR (neat): 3030, 1491, 1092,
837 and 812 cm−1; anal. calcd for C10H11Cl: C, 72.07;
H, 6.65%. Found: C, 72.28; H, 6.76%.
4.4.1. (Z)-1-Phenyl-2-nitropropene 1b. Purified by
column chromatography on silica gel with hexane/ethyl
acetate (20/1); 15% yield; mp 45–46°C; 1H NMR
(CDCl3, TMS): l 2.36 (3H, s), 6.48 (1H, s) and 7.21–
7.37 (5H, m); IR (KBr): 1528 and 1350 cm−1; anal.
calcd for C9H9NO2: C, 66.25; H, 5.56; N, 8.58%.
Found: C, 66.12; H, 5.58; N, 8.53%.
4.6. General procedure for the preparation of 3-aryl-2-
nitro-2-butenes 3
Nitric acid (4.5 g) and sulfuric acid (two drops) were
added dropwise to stirred acetic anhydride (30 mL) at
0°C. A solution of 2-aryl-2-butene (25 mmol) in acetic
anhydride (10 mL) was added dropwise to the mixture.
After 20 min, water (150 mL) was added and the
mixture was stirred for 30 min at room temperature.
The organic materials were extracted with diethyl ether.
The organic layer was neutralized with saturated
sodium hydrogen carbonate, washed with brine, and
dried over anhydrous magnesium sulfate. Evaporation
of the solvent gave crude 3-acetoxy-3-aryl-2-nitro-
butane, which was used without further purification.
4.4.2. (Z)-1-Phenyl-2-nitro-1-butene 1p. Purified by
column chromatography on silica gel with hexane/ethyl
1
acetate (20/1); 19% yield; H NMR (CDCl3, TMS): l
1.21 (3H, t, J=7.4 Hz), 2.69 (2H, q, J=7.4 Hz), 6.37
(1H, s) and 7.22–7.37 (5H, m); IR (neat): 1524 and 1373
cm−1; anal. calcd for C10H11NO2: C, 67.78; H, 6.26; N,
7.90%. Found: C, 67.62; H, 6.28; N, 7.91%.

Y. Kawai et al. / Tetrahedron: Asymmetry 12 (2001) 309–318
315
To a solution of 3-acetoxy-3-aryl-2-nitrobutane in chlo-
roform (50 mL) was added triethylamine (4 mL) and
the mixture was refluxed overnight. The mixture was
neutralized with diluted hydrochloric acid, washed with
brine, and dried over anhydrous magnesium sulfate.
Evaporation of the solvent gave a crude product, which
was purified by column chromatography on silica gel
with hexane/ethyl acetate (20/1). The isolated yields and
their spectral data are shown below.
phy on silica gel with hexane/ethyl acetate (20/1). The
yields and the enantiomeric excesses are summarized in
Table 2. The spectral data are shown below.
4.7.1. 1-Phenyl-2-nitropropane 2a. 1H NMR (CDCl3,
TMS): l 1.54 (3H, d, J=6.7 Hz), 3.00 (1H, dd, J=6.8,
14.0 Hz), 3.32 (1H, dd, J=7.5, 14.0 Hz), 4.69–4.86 (1H,
m) and 7.14–7.32 (5H, m); IR (neat): 1551 cm−1; anal.
calcd for C9H11NO2: C, 65.44; H, 6.71; N, 8.48%.
Found: C, 65.35; H, 6.75; N, 8.45%.
1
4.6.1. (Z)-3-Phenyl-2-nitro-2-butene 3a. 49% yield; H
4.7.2. 1-(2%-Chlorophenyl)-2-nitropropane 2c. 1H NMR
(CDCl3, TMS): l 1.59 (3H, d, J=6.7 Hz), 3.19 (1H, dd,
J=6.1, 14.1 Hz), 3.40 (1H, dd, J=8.1, 14.1 Hz), 4.84–
5.02 (1H, m), 7.16–7.26 (3H, m) and 7.36–7.41 (1H, m);
IR (neat): 1551 cm−1; anal. calcd for C9H10NO2Cl: C,
54.15; H, 5.05; N, 7.02%. Found: C, 54.17; H, 5.21; N,
6.84%.
NMR (CDCl3, TMS): l 2.09 (3H, q, J=1.5 Hz), 2.23
(3H, q, J=1.5 Hz) and 7.18–7.43 (5H, m); IR (neat):
1520 and 1343 cm−1; anal. calcd for C10H11NO2: C,
67.78; H, 6.26; N, 7.90%. Found: C, 67.86; H, 6.31; N,
7.86%.
4.6.2. (E)-3-Phenyl-2-nitro-2-butene 3b. 14% yield; 1H
NMR (CDCl3, TMS): l 2.12 (3H, q, J=1.1 Hz), 2.32
(3H, q, J=1.1 Hz) and 7.13–7.35 (5H, m); IR (neat):
1522 and 1352 cm−1; anal. calcd for C10H11NO2: C,
67.78; H, 6.26; N, 7.90%. Found: C, 67.64; H, 6.42; N,
7.89%.
1
4.7.3. 1-(3%-Chlorophenyl)-2-nitropropane 2d. H NMR
(CDCl3, TMS): l 1.56 (3H, d, J=6.7 Hz), 2.99 (1H, dd,
J=6.5, 14.1 Hz), 3.30 (1H, dd, J=7.7, 14.1 Hz), 4.69–
4.86 (1H, m), 7.02–7.07 (1H, m), 7.17 (1H, s) and
7.24–7.27 (2H, m); IR (neat): 1551 cm−1; anal. calcd for
C9H10NO2Cl: C, 54.15; H, 5.05; N, 7.02%. Found: C,
53.93; H, 5.10; N, 6.86%.
4.6.3. (Z)-3-(2%-Chlorophenyl)-2-nitro-2-butene 3c. 43%
1
yield; H NMR (CDCl3, TMS): l 1.97 (3H, q, J=1.6
Hz), 2.21 (3H, q, J=1.6 Hz), 7.13–7.18 (1H, m), 7.26–
7.34 (2H, m) and 7.43–7.48 (1H, m); IR (neat): 1524
and 1345 cm−1; anal. calcd for C10H10NO2Cl: C, 56.75;
H, 4.76; N, 6.62%. Found: C, 56.79; H, 4.85; N, 6.54%.
4.7.4. 1-(4%-Chlorophenyl)-2-nitropropane 2e. 1H NMR
(CDCl3, TMS): l 1.55 (3H, d, J=6.7 Hz), 2.99 (1H, dd,
J=6.4, 14.1 Hz), 3.29 (1H, dd, J=7.8, 14.1 Hz), 4.67–
4.84 (1H, m), 7.07–7.13 (2H, m) and 7.26–7.32 (2H, m);
IR (neat): 1551 cm−1; anal. calcd for C9H10NO2Cl: C,
54.15; H, 5.05; N, 7.02%. Found: C, 54.34; H, 5.17; N,
6.93%.
4.6.4. (Z)-3-(3%-Chlorophenyl)-2-nitro-2-butene 3d. 34%
1
yield; H NMR (CDCl3, TMS): l 2.09 (3H, q, J=1.5
Hz), 2.19 (3H, q, J=1.5 Hz), 7.07–7.12 (1H, m), 7.20–
7.26 (1H, m) and 7.34–7.36 (2H, m); IR (neat): 1522
and 1345 cm−1; anal. calcd for C10H10NO2Cl: C, 56.75;
H, 4.76; N, 6.62%. Found: C, 56.73; H, 4.81; N, 6.59%.
1
4.7.5. 1-(2%-Methylphenyl)-2-nitropropane 2f. H NMR
(CDCl3, TMS): l 1.55 (3H, d, J=6.6 Hz), 2.33 (3H, s),
2.98 (1H, dd, J=6.9, 13.9 Hz), 3.38 (1H, dd, J=7.5,
13.9 Hz), 4.68–4.88 (1H, m) and 7.04–7.19 (4H, m); IR
(neat): 1551 cm−1; anal. calcd for C10H13NO2: C, 67.02;
H, 7.31; N, 7.82%. Found: C, 66.92; H, 7.38; N, 7.82%.
4.6.5. (Z)-3-(4%-Chlorophenyl)-2-nitro-2-butene 3e. 37%
1
yield; H NMR (CDCl3, TMS): l 2.09 (3H, q, J=1.5
Hz), 2.20 (3H, q, J=1.5 Hz), 7.12–7.19 (2H, m) and
7.37–7.43 (2H, m); IR (neat): 1522 and 1343 cm−1; anal.
calcd for C10H10NO2Cl: C, 56.75; H, 4.76; N, 6.62%.
Found: C, 56.62; H, 4.78; N, 6.54%.
1
4.7.6. 1-(3%-Methylphenyl)-2-nitropropane 2g. H NMR
(CDCl3, TMS): l 1.54 (3H, d, J=6.6 Hz), 2.33 (3H, s),
2.96 (1H, dd, J=6.9, 13.9 Hz), 3.29 (1H, dd, J=7.5,
13.9 Hz), 4.69–4.86 (1H, m) and 6.94–7.26 (4H, m); IR
(neat): 1551 cm−1; anal. calcd for C10H13NO2: C, 67.02;
H, 7.31; N, 7.82%. Found: C, 66.81; H, 7.35; N, 7.77%.
4.7. General procedure for the reduction of a,b-disubsti-
tuted nitroalkenes by baker’s yeast
1
Nitroalkene (2.5 mmol) dissolved in ethanol (5.0 mL)
was added to a stirred suspension of dry baker’s yeast
(25 g) in water (150 mL) at 35°C. The reaction was
followed by gas chromatography. When the substrate
was consumed completely or after 24 h, the reaction
was worked up as follows. Acetone (150 mL) was
added to the reaction mixture and the mixture was
filtered through hyflo super-cel®. The residue was
washed three times with acetone and the washing solu-
tion was combined with the filtrate. The mixture was
evaporated under reduced pressure to 100 mL and the
organic materials were extracted with diethyl ether. The
ether solution was dried over anhydrous magnesium
sulfate. Evaporation of the solvent gave a crude
product, which was purified by column chromatogra-
4.7.7. 1-(4%-Methylphenyl)-2-nitropropane 2h. H NMR
(CDCl3, TMS): l 1.52 (3H, d, J=6.6 Hz), 2.31 (3H, s),
2.96 (1H, dd, J=6.9, 14.3 Hz), 3.27 (1H, dd, J=7.4,
14.3 Hz), 4.66–4.83 (1H, m), 7.04 (2H, d, J=8.1 Hz)
and 7.12 (2H, d, J=8.1 Hz); IR (neat): 1551 cm−1; anal.
calcd for C10H13NO2: C, 67.02; H, 7.31; N, 7.82%.
Found: C, 66.93; H, 7.23; N, 7.67%.
1
4.7.8. 1-(2%-Methoxyphenyl)-2-nitropropane 2i. H NMR
(CDCl3, TMS): l 1.53 (3H, d, J=6.7 Hz), 3.05 (1H, dd,
J=6.5, 13.5 Hz), 3.27 (1H, dd, J=7.7, 13.5 Hz), 3.84
(3H, s), 4.83–5.00 (1H, m) and 6.84–7.30 (4H, m); IR
(neat): 1549 and 1248 cm−1; anal. calcd for C10H13NO3:
C, 61.53; H, 6.71; N, 7.17%. Found: C, 61.27; H, 6.80;
N, 7.11%.

316
Y. Kawai et al. / Tetrahedron: Asymmetry 12 (2001) 309–318
1
4.7.9. 1-(3%-Methoxyphenyl)-2-nitropropane 2j. H NMR
(CDCl3, TMS): l 1.55 (3H, d, J=6.7 Hz), 2.98 (1H, dd,
J=7.0, 13.8 Hz), 3.31 (1H, dd, J=7.4, 13.8 Hz), 3.79
(3H, s), 4.70–4.87 (1H, m), 6.69–6.83 (3H, m) and
7.20–7.28 (1H, m); IR (neat): 1551 and 1263 cm−1; anal.
calcd for C10H13NO3: C, 61.53; H, 6.71; N, 7.17%.
Found: C, 61.81; H, 6.81; N, 7.12%.
(2H, d, J=8.3 Hz) and 7.11 (2H, d, J=8.3 Hz); IR
(neat): 1551 cm−1; anal. calcd for C11H15NO2: C, 68.37;
H, 7.82; N, 7.25%. Found: C, 68.18; H, 7.88; N, 7.29%.
4.8. General procedure for the reduction of trisubsti-
tuted nitroalkenes by baker’s yeast
The procedure described for a,b-disubstituted
nitroalkenes was followed using baker’s yeast (50 g)
and water (250 mL). The yields, diastereomeric
excesses, and enantiomeric excesses are summarized in
Table 3. The spectral data are shown below.
4.7.10. 1-(4%-Methoxyphenyl)-2-nitropropane 2k. 1H
NMR (CDCl3, TMS): l 1.53 (3H, d, J=6.7 Hz), 2.95
(1H, dd, J=6.7, 14.1 Hz), 3.25 (1H, dd, J=7.5, 14.1
Hz), 3.78 (3H, s), 4.65–4.82 (1H, m) and 7.14–7.32 (4H,
m); IR (neat): 1549 and 1245 cm−1; anal. calcd for
C10H13NO3: C, 61.53; H, 6.71; N, 7.17%. Found: C,
61.55; H, 6.88; N, 7.09%.
4.8.1. (2R,3R)-3-Phenyl-2-nitrobutane 4a. [h]2D0=+8.5 (c
1.0, EtOH), e.e.=98%; 1H NMR (CDCl3, TMS): l 1.31
(3H, d, J=6.6 Hz), 1.32 (3H, d, J=6.9 Hz), 3.22 (1H,
dq, J=10.0, 6.9 Hz), 4.67 (1H, dq, J=10.0, 6.6 Hz) and
7.15–7.40 (5H, m); IR (neat): 1551 cm−1; anal. calcd for
C10H13NO2: C, 67.02; H, 7.31; N, 7.82%. Found: C,
66.89; H, 7.38; N, 7.81%.
4.7.11. 1-Cyclohexyl-2-nitropropane 2l. 1H NMR
(CDCl3, TMS): l 0.80–2.04 (16H, m) and 4.61–4.79
(1H, m); IR (neat): 2926, 2853 and 1551 cm−1; anal.
calcd for C9H17NO2: C, 63.13; H, 10.00; N, 8.18%.
Found: C, 62.94; H, 10.08; N, 8.12%.
4.8.2. (2S,3R)-3-Phenyl-2-nitrobutane 5a. [h]2D0=+91.5
1
(c 1.0, EtOH), e.e.=97%; H NMR (CDCl3, TMS): l
1
4.7.12. 4-Methyl-2-nitropentane 2m. H NMR (CDCl3,
1.33 (3H, d, J=7.2 Hz), 1.56 (3H, d, J=6.7 Hz), 3.38
(1H, dq, J=8.4, 7.2 Hz), 4.72 (1H, dq, J=8.4, 6.7 Hz)
and 7.17–7.37 (5H, m); IR (neat): 1549 cm−1; anal.
calcd for C10H13NO2: C, 67.02; H, 7.31; N, 7.82%.
Found: C, 66.91; H, 7.42; N, 7.81%.
TMS): l 0.92 (3H, d, J=6.5 Hz), 0.96 (3H, d, J=6.3
Hz), 1.40–1.62 (5H, m), 1.92–2.03 (1H, m) and 4.62–
4.72 (1H, m); IR (neat): 1553 cm−1; anal. calcd for
C6H13NO2: C, 54.94; H, 9.99; N, 10.68%. Found: C,
55.18; H, 10.18; N, 10.46%.
4.8.3. (2R,3R)-3-(3%-Chlorophenyl)-2-nitrobutane 4d.
[h]2D0=+7.5 (c 1.0, EtOH), e.e.=82%; 1H NMR (CDCl3,
TMS): l 1.31 (3H, d, J=6.9 Hz), 1.33 (3H, d, J=6.6
Hz), 3.22 (1H, dq, J=9.9, 6.9 Hz), 4.64 (1H, dq,
J=9.9, 6.6 Hz), 7.04–7.10 (1H, m), 7.17–7.19 (1H, m)
and 7.26–7.30 (2H, m); IR (neat): 1553 cm−1; anal.
calcd for C10H12NO2Cl: C, 56.21; H, 5.66; N, 6.56%.
Found: C, 56.38; H, 5.69; N, 6.44%.
4.7.13. 4,4-Dimethyl-2-nitropentane 2n. 1H NMR
(CDCl3, TMS): l 0.93 (9H, s), 1.04 (1H, dd, J=3.7, 8.8
Hz), 1.53 (3H, d, J=6.7 Hz), 2.21 (1H, dd, J=8.8, 15.1
Hz) and 4.63–4.79 (1H, m); anal. calcd for C7H15NO2:
C, 57.90; H, 10.41; N, 9.65%. Found: C, 58.81; H,
10.57; N, 10.19%.
4.7.14. 1-Phenyl-2-nitrobutane 2o. 1H NMR (CDCl3,
TMS): l 0.98 (3H, t, J=7.4 Hz), 1.73–2.14 (2H, m),
3.03 (1H, dd, J=5.9, 14.1 Hz), 3.26 (1H, dd, J=8.5,
14.1 Hz), 4.56–4.70 (1H, m) and 7.13–7.36 (5H, m); IR
(neat): 1549 cm−1; anal. calcd for C10H13NO2: C, 67.02;
H, 7.31; N, 7.82%. Found: C, 66.78; H, 7.34; N, 7.79%.
4.8.4. (2S,3R)-3-(3%-Chlorophenyl)-2-nitrobutane 5d.
[h]2D0=+54.8 (c 0.90, EtOH), e.e.=81%; 1H NMR
(CDCl3, TMS): l 1.32 (3H, d, J=7.2 Hz), 1.57 (3H, d,
J=6.7 Hz), 3.36 (1H, dq, J=8.6, 7.2 Hz), 4.70 (1H, dq,
J=8.6, 6.7 Hz), 7.06–7.11 (1H, m) and 7.18–7.26 (3H,
m); IR (neat): 1549 cm−1; anal. calcd for C10H12NO2Cl:
C, 56.21; H, 5.66; N, 6.56%. Found: C, 56.39; H, 5.75;
N, 6.35%.
1
4.7.15. 1-(2%-Methylphenyl)-2-nitrobutane 2q. H NMR
(CDCl3, TMS): l 0.98 (3H, t, J=7.3 Hz), 1.73–2.17
(2H, m), 2.33 (3H, s), 3.05 (1H, dd, J=6.1, 14.4 Hz),
3.28 (1H, dd, J=8.3, 14.4 Hz), 4.54–4.69 (1H, m) and
7.06–7.18 (4H, m); IR (neat): 1551 cm−1; anal. calcd for
C11H15NO2: C, 68.37; H, 7.82; N, 7.25%. Found: C,
68.21; H, 7.91; N, 7.16%.
4.8.5. (2R,3R)-3-(4%-Chlorophenyl)-2-nitrobutane 4e.
[h]2D0=+8.2 (c 1.0, EtOH), e.e.=94%; 1H NMR (CDCl3,
TMS): l 1.31 (3H, d, J=6.9 Hz), 1.32 (3H, d, J=6.6
Hz), 3.23 (1H, dq, J=9.8, 6.9 Hz), 4.62 (1H, dq,
J=9.8, 6.6 Hz), 7.12 (2H, dt, J=8.9, 2.3 Hz) and 7.33
(2H, dt, J=8.9, 2.3 Hz); IR (neat): 1551 cm−1; anal.
calcd for C10H12NO2Cl: C, 56.21; H, 5.66; N, 6.56%.
Found: C, 56.29; H, 5.69; N, 6.56%.
1
4.7.16. 1-(3%-Methylphenyl)-2-nitrobutane 2r. H NMR
(CDCl3, TMS): l 0.97 (3H, t, J=7.4 Hz), 1.72–2.13
(2H, m), 2.32 (3H, s), 2.98 (1H, dd, J=6.0, 14.1 Hz),
3.22 (1H, dd, J=8.5, 14.1 Hz), 4.55–4.69 (1H, m) and
6.93–7.24 (4H, m); IR (neat): 1551 cm−1; anal. calcd for
C11H15NO2: C, 68.37; H, 7.82; N, 7.25%. Found: C,
68.46; H, 7.95; N, 7.10%.
4.8.6. (2S,3R)-3-(4%-Chlorophenyl)-2-nitrobutane 5e.
[h]2D0=+82.6 (c 1.0, EtOH), e.e.=92%; 1H NMR
(CDCl3, TMS): l 1.33 (3H, d, J=7.2 Hz), 1.57 (3H, d,
J=6.7 Hz), 3.34 (1H, dq, J=8.7, 7.2 Hz), 4.68 (1H, dq,
J=8.7, 6.7 Hz), 7.13 (2H, dt, J=8.7, 2.2 Hz) and 7.29
(2H, dt, J=8.7, 2.2 Hz); IR (neat): 1551 cm−1; anal.
calcd for C10H12NO2Cl: C, 56.21; H, 5.66; N, 6.56%.
Found: C, 56.29; H, 5.70; N, 6.52%.
1
4.7.17. 1-(4%-Methylphenyl)-2-nitrobutane 2s. H NMR
(CDCl3, TMS): l 0.97 (3H, t, J=7.4 Hz), 1.72–2.12
(2H, m), 2.31 (3H, s), 2.98 (1H, dd, J=5.9, 14.0 Hz),
3.21 (1H, dd, J=8.5, 14.0 Hz), 4.53–4.67 (1H, m), 7.03

Y. Kawai et al. / Tetrahedron: Asymmetry 12 (2001) 309–318
317
4.9. Determination of enantiomeric excess of nitro-
alkane
Acknowledgements
Anhydrous ammonium formate (7 mmol) was added to
a stirred suspension of nitroalkane (1 mmol) and palla-
dium on carbon (10%, 0.05 g) in dry methanol (2 mL)
and the mixture was stirred for 6 h at room tempera-
ture under an atmosphere of argon. The mixture was
filtered and the filtrate was evaporated at reduced pres-
sure. The residue was dissolved in a mixture of ethyl
acetate and water. The organic layer was separated and
dried over anhydrous magnesium sulfate. Evaporation
of the solvent gave a corresponding amine, which was
used without further purification.
This work was partially supported by a Grant-in-Aid
for Scientific Research No. 12680634 from the Ministry
of Education, Science, Sports, and Culture of Japan.
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,
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