Biocatalytic asymmetric reduction of 3-acetylisoxazoles

Article abstract of DOI:10.1016/j.tetasy.2005.02.024

The reduction of the carbonyl group in 3-acetylisoxazole derivatives by algae (Cyanobacterium: Synechococcus elongatus PCC 7942 and Synechosystis sp. PCC 6803) and plant cells (Caragana chamlagu) gave the corresponding (S)-alcohols with high enantioselect

Full text of DOI:10.1016/j.tetasy.2005.02.024

Tetrahedron:
Asymmetry
Tetrahedron: Asymmetry 16 (2005) 1403–1408
Biocatalytic asymmetric reduction of 3-acetylisoxazoles
Ken-ichi Itoh,a,* Hiroshi Sakamaki,a Kaoru Nakamurab and C. Akira Horiuchic
aCollege of Science and Technology, Nihon University, 7-24-1 Funabashi-si, Chiba 274-8501, Japan
bInstitute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan
cDepartment of Chemistry, Rikkyo (St. PaulÕs) University, Nishi-Ikebukuro, Toshima-ku, Tokyo 171-8501, Japan
Received 18 January 2005; accepted 21 February 2005
Abstract—The reduction of the carbonyl group in 3-acetylisoxazole derivatives by algae (Cyanobacterium: Synechococcus elongatus
PCC 7942 and Synechosystis sp. PCC 6803) and plant cells (Caragana chamlagu) gave the corresponding (S)-alcohols with high
enantioselectivities.
Ó 2005 Elsevier Ltd. All rights reserved.
1. Introduction
cyanobacterium and the plant-cultured cells of Caragana
chamlagu. Herein, we report an efficient asymmetric
reduction of the heterocyclic carbonyl compounds,
3-acetylisoxazoles with these biocatalysts.
Isoxazole heterocycles have been employed in a wide
variety of starting materials in organic chemistry.
Isoxazoles can be converted into synthetically useful
functional building blocks such as a,b-unsaturated
oximes,1 b-hydroxy ketones,2 and c-amino alcohols.3
Additionally, isoxazole derivatives,4,5 in particular,
those with hydroxyl functionalities,6 express a wide
range of interesting pharmacological properties. Re-
cently, we have reported a novel one-pot synthesis of
3-acetylisoxazole derivatives using ammonium cerium
nitrate (CAN).7 The reaction of alkenes and alkynes
with CAN in acetone under reflux gave the correspond-
ing 3-acetylisoxazole derivatives in good yields.
2. Results and discussion
2.1. Reduction of 3-acetylisoxazole derivatives by
cyanobacterium
The substrates for biotransformation were prepared
from the corresponding alkynes according to Scheme 1.7
N
O
CAN(III) / formic acid
Acetone / reflux
From the viewpoint of Ôgreen chemistryÕ, biocatalysts
have been used for the transformation of natural or arti-
ficial substrates into useful compounds.8 Among them,
we have so far developed the use of plant cultured cells
for the biotransformation of natural products such as
thujopsene9 and ionone10 and unnatural substrates such
as 1,2-diketone.11 Among photosynthetic organisms
such as microalgae and higher plants, other than con-
ventional yeasts and fungi, are especially very useful
for biocatalytic reduction, a method for preparing opti-
cally active compounds. Acetophenone derivatives,12
camphorquinones,13 and 1,3-diketones14 could be
reduced with high enantioselectivities by applying a
R
R
O
CAN(III) : (NH4)2Ce(NO3)5
Scheme 1. One-pot synthesis of 3-acetylisoxazoles.
First, the reaction of 3-acetyl-5-propylisoxazole 1a with
S. elongatus PCC 7942 was investigated. These results
are summarized in Table 1 and Scheme 2. When 3-acet-
yl-5-propylisoxazole 1a was added to the suspension
of S. elongatus PCC 7942 and shaken under dark condi-
tions, no reduction occurred (Table 1, run 12). However,
the reduction of 1a proceeded when the reaction was
done under illumination with fluorescence light
(2000 lux). After 96 h, the corresponding (S)-alcohol
1b was obtained in 67% yield (92% ee) (Table 1, run 8).
*
Corresponding author. Tel./fax: +81 80 47 469 5477; e-mail: k-itoh@
chem.ge.cst.nihon-u.ac.jp
0957-4166/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetasy.2005.02.024

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K. Itoh et al. / Tetrahedron: Asymmetry 16 (2005) 1403–1408
Table 1. Reduction of 3-acetyl-5-propylisoxazole 1a by Synechococcus
elongatus PCC 7942
PCC 7942 were carried out (Scheme 2, Table 2). It is
noteworthy that all substrates were reduced to the corre-
sponding (S)-alcohol in moderate chemical yields with
91–96% ee. The substrate specificities of the cyanobacte-
rium are wide. Thus, propyl, hexyl, phenyl, and chlo-
romethyl derivatives were reduced in high yields, with
92–96% ee, however, the yields of 5-bromomethyl deriv-
atives 6b were low (21%). Ketones 6a seemed to be poor
substrates, as no significant degradation of either 6a or
the product 6b was observed under incubation condi-
tions. Another cyanobacterium, Synechocystis sp. PCC
6803 could be used13 with the same isomers obtained
in high ee (>91%) (Table 3).
Run
Substrate
(1a/mg)
Time (h)
Yield (%)a,b
Ee (%)
(Config.)
1
10
25
50
75
25
25
25
25
25
25
25
25
144
144
144
144
24
62
66
91 (S)
92 (S)
92 (S)
89 (S)
86 (S)
89 (S)
89 (S)
92 (S)
92 (S)
—
2
3
44
12
4
5
11
24
6
48
72
7
49
67
8
96
9
120
120
120
120
67
10c
11d
12e
No reaction
No reaction
No reaction
—
—
Table 2. Reduction of 3-acetylisoxazoles (2a–7a) with Synechococcus
elongatus PCC 7942
a Compound 1b was obtained.
b Determined by GC analysis using n-dodecane as the internal
hydrocarbon standard.
c The reaction without the microbe.
d The dried cells of S. elongatus PCC 7942 were used.
e The reaction proceeded in the dark.
Run
Substrate
Yield (%)a
Ee (%) (Config.)
1
2
3
4
5
6
2a
3a
4a
5a
6a
7a
2b (55)
3b (54)
4b (47)
5b (57)
6b (21)
7b (53)
92 (S)
95 (S)
96 (S)
93 (S)
91 (S)
92 (S)
N
O
N
O
a Determined by GC analysis using n-dodecane as the internal hydro-
carbon standard.
S. elongatus PCC 7942
R
R
O
OH
1b-7b
1a : R=n-C3H7 5a : R=Ph
2a : R=n-C4H9 6a : R=CH2Br
3a : R=n-C5H11 7a : R=CH2Cl
4a : R=n-C6H13
Table 3. Reduction of 2a–7a with Synechocystis sp. PCC 6803
1a-7a
Run
Substrate
Yield (%)a
Ee (%) (Config.)
1
2
3
4
5
6
7
1a
2a
3a
4a
5a
6a
7a
1b (53)
2b (50)
3b (49)
4b (48)
5b (52)
6b (20)
7b (50)
91 (S)
91 (S)
95 (S)
95 (S)
91 (S)
91 (S)
92 (S)
Scheme 2.
Upon increasing the amount of 1a, the chemical yield
decreased according to the amount of 1a. The time
course of the reaction is shown in Figure 1. The reaction
required 96 h to obtain a high yield. Since the amount of
microbe used in the reaction was 20–30 mg (dry weight),
the catalyst/substrate ratio of the reaction was 1:2. This
ratio was superior to that in the conventional use of
BakerÕs yeast.15
a Determined by GC analysis using n-dodecane as the internal hydro-
carbon standard.
The reduction of the carbonyl groups in the methyl het-
erocyclic ketones such as acetylpyridine [85% ee (S)]16
and 2-isoxazoline [98% ee (S)]17 with BakerÕs yeast was
reported. The acetylpyridine derivatives [97% ee (R)]18
and acetylthiophenes [>99% ee (S)]19 were reduced with
Candida maris and Geotrichum candidum, respectively.
With the exception for Candida maris, the other mi-
crobes afforded (S)-alcohols upon reduction. Although
the enantioselectivities of the product alcohols in the
present reduction are slightly low compared to the
reduction of 2-isoxazoline with bakerÕs yeast, the biocat-
alyst/substrate ratio is superior when a cyanobacterium
was used as the biocatalyst (cyanobacterium = 1 and
BakerÕs yeast = 20).
100
90
80
N
O
70
60
50
40
30
20
10
0
C H
3
7
O
O
N
C H
3
7
OH
2.2. Reduction of 3-acetylisoxazole derivatives by
C. chamlagu
0
24
48
72
96
120
Time / h
Figure 1. Time course for reduction of 3-acetyl-5-propylisoxazole by
Synechococcus elongatus PCC 7942.
In contrast to cyanobacterium, the reduction of ketone
1a and other substrates (Table 4) by applying the
plant-cultured cells of C. chamlagu proceeded more eas-
ily than those by cyanobacterium. For example, the
alcohol (S)-1b was obtained in 72% yield and 94% ee
On the basis of these reaction conditions, reductions
using other 3-acetylisoxazoles 2a–7a by S. elongatus

K. Itoh et al. / Tetrahedron: Asymmetry 16 (2005) 1403–1408
Table 4. Reduction of 1a with Caragana chamlagu Table 6. Reduction of 2a–7a with Caragana chamlagu
1405
Run
Substrate
(1a/mg)
Time (h)
Yield (%)a,b
Ee (%) (Config.)
Run
Substrate
Time (h)
Yield (%)a
Ee (%) (Config.)
1
2
3
4
5
6
2a
3a
4a
5a
6a
7a
12
12
12
24
15
15
2b (72)
3b (76)
4b (75)
5b (88)
6b (41)
7b (82)
95 (S)
95 (S)
97 (S)
99 (S)
98 (S)
97 (S)
1
10
20
40
60
80
20
20
20
20
20
20
24
24
48
48
48
1
70
72
59
46
16
18
48
66
72
72
71
94 (S)
94 (S)
94 (S)
94 (S)
91 (S)
92 (S)
93 (S)
94 (S)
94 (S)
94 (S)
94 (S)
2
3
4
5
6
a Determined by GC analysis using n-dodecane as the internal hydro-
carbon standard.
7
3
8
6
9
9
10
11
12
48
4). The reduction of sterically hindered ketone 6a
proceeded more efficiently (6b: 41%) than those by
cyanobacterium as described above (Table 6, run 5).
a Compound 1b was obtained.
b Determined by GC analysis using n-dodecane as the internal
hydrocarbon standard.
There is an advantage in the use of cultured plant cells.
Although the efficiency (biocatalyst/substrate ratio) in
the reduction with the cyanobacterium was better than
that with the plant cells, the increase of cyanobacterial
cell concentration is very difficult because of necessity
of light for the progress of the reduction. The problem
caused by the low activity of the plant cells can be over-
come by increasing the concentration.
100
90
O
N
80
70
60
50
40
30
20
10
0
C H
3
7
O
O
N
2.3. Absolute configuration of 3-(1-hydroxyethyl)-5-
alkyllisoxazole 1b–7b
C H
3
7
OH
The absolute configuration of product alcohols 1b–7b
from the reduction of 1a–7a with biocatalysts was deter-
mined as follows. The Mosher esters20 of 1b–7b (racemic
and biocatalytic product) with (S)-(+)-MTPA-Cl were
prepared and their 1H NMR spectra measured with
the results listed in Table 7. The Mosher esters derived
from (S)-(+)-MTPA-Cl with the (R)- or (S)-isomer
0
3
6
9
12
Time / h
Figure 2. Time course for reduction of 3-acetyl-5-propylisoxazole by
Caragana chamlagu.
(Table 4, run 9). The time course of the progress of this
reaction is shown in Figure 2.
Table 7. 1H NMR chemical shift of Mosher esters
Next we attempted the elaboration of the incubation
conditions (Table 5). The reduction by C. chamlagu
was independent of either light or initial pH conditions.
Various 3-acetylisoxazoles 2a–7a were incubated (Table
6), and the corresponding (S)-alcohols obtained; for
example, (S)-5b in 88% yield and 99% ee (Table 6, run
Mosher estersa
–CH3 (methyl)
–CH2– (methylene)
( )-1bb
1.63
1.71
1.71
1.63
1.7
2.71
2.66
2.66
2.73
2.69
2.69
2.72
2.68
2.68
2.72
2.68
2.68
—
1b
( )-2bb
2b
( )-3bb
1.7
1.63
1.7
Table 5. Reaction conditions for the reduction of 1a with Caragana
chamlagu
3b
( )-4bb
1.7
Run Condition pH in culture Yield (%)a,b Ee (%) (Config.)
medium
1.63
1.7
1c
2d
3
Dark
Dark
Dark
Dark
Dark
Light
Light
Light
Light
5.8
5.8
4.0
7.0
8.5
4.0
5.8
7.0
8.5
No reaction
No reaction
—
—
4b
( )-5bb
1.7
1.7
70
68
69
69
70
70
67
94 (S)
94 (S)
94 (S)
94 (S)
94 (S)
94 (S)
94 (S)
1.77
1.77
1.65
1.72
1.72
1.65
1.72
1.72
—
—
4
5b
( )-6bb
5
4.59
4.55
4.55
4.59
4.55
4.55
6
7
6b
( )-7bb
8
9
7b
a Compound 1b was obtained.
b Determined by GC analysis using n-dodecane as the internal
hydrocarbon standard.
a Alcohol (0.1 mmol), (S)-(+)-MTPA-Cl (0.4 mmol), pyridine (0.1 mL)
and tetrachloride (1.0 mL) were employed.
b Alcohol (0.1 mmol), NaBH4 (0.3 mmol) and Et2O (10.0 mL) were
employed.
c The reaction without the plant-cultured cells.
d The cells of C. chamlagu were dried.

1406
K. Itoh et al. / Tetrahedron: Asymmetry 16 (2005) 1403–1408
downfield
H3C
upfield
O
O
N
N
n-Pr
S
n-Pr
R
CH3
CH3O
CH3O
CF3
CF3
N
O
n-Pr
OH
1b
Scheme 3. Absolute configuration.
would give configurations as shown in Scheme 3. In this
configuration, the methyl group (CH–CH3) in the
(R)-isomer faces the phenyl ring in the (S)-MTPA and
should exhibit an upfield chemical shift relative to the
(S)-isomer in the NMR spectrum.21
uous illumination provided by fluorescent lamps
(2000 lux) with air-bubbling at 25 °C. The callus tissues
used in this experiment were derived from the leaves of
C. chamlagu and maintained in our laboratory for eight
years on agar plate containing an MS medium (pH 5.8)
plus 3% sucrose and 2,4-dichlorophonoxacetic acid at
25 °C in the dark.9a
In the present experiment, all of the (S)-(+)-MTPA esters
of the alcohols from the biocatalytic reduction of the 3-
acetylisoxazoles afforded downfield methyl signals than
those of the isomers in the 1H NMR spectra. The config-
urations of the products were then determined to be (S).
Also, the NMR spectrum in the methylene group of the
side chain shows a characteristic upfield chemical shift.
4.3. Typical procedures: reduction of 3-acetylisoxazole
derivatives by cyanobacterium (S. elongatus PCC 7942
and Synechosystis sp. PCC 6803)
3-Acetylisoxazole derivatives 1a–7a (25 mg) were added
to the suspended culture of S. elongatus PCC 7942 or
Synechosystis sp. PCC 6803 (1 g/L as dry weight) in a
BG-11 medium (50 mL). The mixture was shaken at
120 rpm and 25 °C in the fluorescence light illumination
(2000 lux). The resulting mixture was extracted with
EtOAc. The chemical and enantiomeric purities were
determined by GC analyses. For the enantiomeric puri-
ties, the GC conditions and retention times of the prod-
ucts are as follows: tR/min; 1b: (120 °C) 5.3 (R), 5.4 (S);
2b: (120 °C) 6.7 (R), 6.8 (S); 3b: (120 °C) 8.9 (R), 9.0 (S);
4b: (120 °C) 13.0 (R), 13.2 (S); 5b: (160 °C) 5.8 (R), 6.5
(S); 6b: (120 °C) 5.8 (R), 6.5 (S); 7b: (120 °C) 11.7 (R),
12.2 (S).
3. Conclusion
In conclusion, the present study revealed some charac-
teristic feature and potency of cyanobacterium and
cultured cell, in the biocatalytic reduction of various
heterocyclic, isoxazole ketones to provide the optically
active forms of the corresponding alcohols.
4. Experimental
4.1. General
4.4. Typical procedures: reduction of 3-acetylisoxazole
derivatives by C. chamlagu
The IR spectra were recorded using a Jasco FT-IR 230
1
spectrometer. The H and 13C NMR spectra were mea-
sured using a JEOL GSX 400 Model spectrometer in
deuteriochloroform solutions with tetramethylsilane as
the internal standard. The gas chromatographic analy-
ses were performed using a chiral GC-column (CP-
cyclodextrin-B-2,3,6-M-19 [CPCD]; 25 m) attached to
a Shimazu GC-17A and a GC-column (DB-1, 25 m)
attached to a Shimazu GC-14A. S. elongatus PCC
7942 and Synechosystis sp. PCC 6803 were obtained
from the Institu Pasteur.
The callus tissues (5 g) of C. chamlagu were transferred
to an MS medium (50 mL) containing 2 ppm of 2,4-D
and 3% sucrose. Then the 3-acetylisoxazole derivatives
1a–7a (20 mg) were added to this suspension. The mix-
ture was shaken at 120 rpm at 25 °C in the dark. The
resulting mixture was filtered to separate the callus tis-
sues and extracted with EtOAc. The chemical and enan-
tiomeric purities were determined by GC analyses.
4.4.1. 3-(1-Hydroxyethyl)-5-propylisoxazole 1b. Pale-
4.2. Cultivation
yellow oil; IR (NaCl) 3387 and 1601 cmÀ1
;
[a]D = À17.4 (c 0.38, CHCl3); 1H NMR (CDCl3)
d = 6.00 (s, 1H), 4.99–5.00 (m, 1H), 2.71 (t, J = 7.56,
2H), 2.34 (br s, 1H), 1.68–1.77 (m, 2H), 1.54 (d,
S. elongatus PCC 7942 and Synechosystis sp. PCC 6803
were grown in a BG-11 medium (pH 8.0) under contin-

K. Itoh et al. / Tetrahedron: Asymmetry 16 (2005) 1403–1408
1407
J = 6.56, 3H) and 0.99 (t, J = 7.56, 3H); 13C NMR
(CDCl3) d = 174.0, 167.4, 98.2, 63.5, 28.7, 22.8, 20.9
and 13.7; HRMS found: m/z 155.0947 [M]+. Calcd for
C8H13NO2: 155.0946.
4.5. Preparation of Mosher ester (a-methoxy-a-tri-
22
fluoromethylphenylacetyl derivatives)
(+)-a-Methoxy-a-trifluoromethylphenylacetyl chloride
[(S)-(+)-MTPA-Cl, 100 mg, 0.40 mmol] was added to a
mixture of alcohol (0.1 mmol) and pyridine (0.1 mL) in
carbon tetrachloride (1.0 mL) at 0–5 °C. The resulting
mixture was stirred at room temperature for 2 h and
then extracted with diethyl ether (30 mL).
4.4.2. 3-(1-Hydroxyethyl)-5-butylisoxazole 2b. Pale-
yellow oil; IR (NaCl) 3395 and 1601 cmÀ1
;
[a]D = À23.6 (c 0.28, CHCl3); 1H NMR (CDCl3)
d = 6.01 (s, 1H), 4.95–5.00 (m, 1H), 2.72 (t, J = 7.32,
2H), 2.17 (br s, 1H), 1.64–1.71 (m, 2H), 1.53 (d,
J = 6.59, 3H), 1.32–1.44 (m, 2H) and 0.94 (t, J = 7.32,
3H); 13C NMR (CDCl3) d = 174.1, 167.6, 98.2, 63.3,
29.6, 26.5, 22.8, 22.2 and 13.7; HRMS found: m/z
169.1102 [M]+. Calcd for C9H15NO2: 169.1102.
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4.4.3. 3-(1-Hydroxyethyl)-5-pentylisoxazole 3b. Pale-
yellow oil; IR (NaCl) 3387 and 1601 cmÀ1
;
[a]D = À17.6 (c 0.41, CHCl3); 1H NMR (CDCl3)
d = 6.01 (s, 1H), 4.95–5.00 (m, 1H), 2.72 (t, J = 7.56,
2H), 2.17 (br s, 1H), 1.65–1.73 (m, 2H), 1.53 (d,
J = 6.59, 3H), 1.31–1.39 (m, 4H) and 0.91 (t, J = 7.56,
3H); 13C NMR (CDCl3) d = 174.1, 167.6, 98.2, 63.2,
31.3, 27.2, 26.7, 22.8, 22.3, and 13.9; HRMS found:
m/z 183.1242 [M]+. Calcd for C10H17NO2: 183.1249.
4.4.4. 3-(1-Hydroxyethyl)-5-hexylisoxazole 4b. Pale-
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;
[a]D = À22.0 (c 0.30, CHCl3); 1H NMR (CDCl3)
d = 6.00 (s, 1H), 4.95–5.00 (m, 1H), 2.72 (t, J = 7.56,
2H), 2.17 (br s, 1H), 1.65–1.72 (m, 2H), 1.53 (d,
J = 6.59, 3H), 1.29–1.39 (m, 6H) and 0.89 (t, J = 7.56,
3H); 13C NMR (CDCl3) d = 174.1, 167.6, 98.2, 63.2,
31.4, 28.8, 27.5, 26.8, 22.8, 22.5 and 14.0; HRMS found:
m/z 197.1406 [M]+. Calcd for C11H19NO2: 197.1406.
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4.4.5. 3-(1-Hydroxyethyl)-5-phenylisoxazole 5b. Pale-
yellow oil; IR (NaCl) 3387 and 1601 cmÀ1
;
[a]D = À24.0 (c 0.25, CHCl3); 1H NMR (CDCl3)
d = 7.79–7.88 (m, 2H), 7.43–7.53 (m, 3H), 6.78 (s, 1H),
4.94–4.99 (m, 1H), 2.15 (br s, 1H) and 1.55 (d,
J = 6.59, 3H); 13C NMR (CDCl3) d = 171.2, 170.2,
131.3, 130.1, 128.8, 126.8, 98.5, 63.7 and 23.1; HRMS
found: m/z 189.0791 [M]+. Calcd for C11H11NO2:
189.0790.
13. Utsukihara, T.; Chai, W.; Kato, N.; Nakamura, K.;
Horiuchi, C. A. J. Mol. Catal. B: Enzym. 2004, 31, 19–24.
14. Chai, W.; Sakamaki, H.; Kitanaka, S.; Horiuchi, C. A.
Bull. Chem. Soc. Jpn. 2003, 76, 177–182.
15. (a) Nakamura, K.; Yamanaka, R. Tetrahedron: Asymme-
try 2003, 14, 2659–2681; (b) Nakamura, K.; Matsuda, T.
In Enzyme Catalysis in Organic Synthesis A Comprehensive
Handbook; Drauz, K., Waldmann, H., Eds.; Wiley-VCH:
Weinheim, 2002, pp 991–1047.
4.4.6. 3-(1-Hydroxyethyl)-5-bromomethylisoxazole 6b.
Pale-yellow oil; IR (NaCl) 3380 and 1605 cmÀ1
;
[a]D = À12.0 (c 0.35, CHCl3); 1H NMR (CDCl3)
d = 6.49 (s, 1H), 4.86–4.91 (m, 1H), 4.61 (s, 2H), 2.15
(br s, 1H) and 1.48 (d, J = 6.59, 3H); 13C NMR (CDCl3)
d = 169.9, 169.5, 102.6, 63.6, 23.0 and 19.3; HRMS
found: m/z 204.9741 [M]+. Calcd for C6H8NO2Br:
204.9738.
16. Bajiley, D.; OÕHangan, D.; Dyer, U.; Lamont, R. B.
Tetrahedron: Asymmetry 1993, 4, 1255–1258.
17. Ticozzi, C.; Zanarotti, A. Tetrahedron Lett. 1988, 29,
6167–6170.
18. Kawano, S.; Horikawa, N.; Yasohara, Y.; Hasegawa, J.
Biosci. Biotech. Biochem. 2003, 67, 809–814.
19. Matsuda, T.; Harada, T.; Nakajima, N.; Itoh, T.;
Nakamura, K. J. Org. Chem. 2000, 65, 157–163.
20. Ohtani, I.; Kusumi, T.; Kashman, Y.; Kakisawa, H.
J. Am. Chem. Soc. 1991, 113, 4092–4096.
4.4.7. 3-(1-Hydroxyethyl)-5-chloromethylisoxazole 7b.
Pale-yellow oil; IR (NaCl) 3374 and 1607 cmÀ1
;
[a]D = À15.8 (c 0.39, CHCl3); 1H NMR (CDCl3)
d = 6.49 (s, 1H), 4.87–4.92 (m, 1H), 4.74 (s, 2H), 2.15
(br s, 1H) and 1.48 (d, J = 6.59, 3H); 13C NMR (CDCl3)
d = 169.8, 169.4, 102.7, 63.6, 35.0 and 23.0; HRMS
found: m/z 161.0245 [M]+. Calcd for C6H8NO2Cl:
161.0244.

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K. Itoh et al. / Tetrahedron: Asymmetry 16 (2005) 1403–1408
21. Nakamura, K.; Takenaka, K. Tetarehedron: Asymmetry
2002, 13, 415–422.
22. (a) Dale, J. A.; Mosher, H. S. J. Am. Chem. Soc. 1973, 95,
512–519; (b) Trost, B. M.; Belletire, J. L.; Godleski, S.;
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