Asymmetric epoxidation of (Z)-enol esters catalyzed by titanium(salalen) complex with aqueous hydrogen peroxide

Article abstract of DOI:10.1016/j.tet.2011.06.022

Titanium(salalen) complex 1 was an effective catalyst for asymmetric epoxidation of enol esters. Although (E)-enol esters were reluctant to proceed, (Z)-enol esters underwent asymmetric epoxidation to give the epoxides in high yields with high enantioselectivity ranging from 86 to >99% ee in the presence of aqueous hydrogen peroxide as the stoichiometric oxidant. Complete enantioselectivity was observed in the reaction of (Z)-3,3-dimethylbut-1-en-1-yl 4-methoxybenzoate. The obtained epoxide was readily transformed into the corresponding 1,2-diol by reduction with lithium borohydride without erosion of the high enantiomeric excess.

Full text of DOI:10.1016/j.tet.2011.06.022

Tetrahedron 67 (2011) 6474e6478
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Asymmetric epoxidation of (Z)-enol esters catalyzed by titanium(salalen) complex
with aqueous hydrogen peroxide
,
,
,c,
*
Kazuhiro Matsumoto a b, Chao Feng a, Satoshi Handa a, Takuya Oguma a b, Tsutomu Katsuki b
a Department of Chemistry, Faculty of Science, Graduate School, Kyushu University, 6-10-1 Hakozaki, Higashi-ku, Fukuoka 812-8581, Japan
b International Institute for Carbon-Neutral Energy Research (I2CNER), Kyushu University, Japan
c Institute for Advanced Study, Kyushu University, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Titanium(salalen) complex 1 was an effective catalyst for asymmetric epoxidation of enol esters. Al-
though (E)-enol esters were reluctant to proceed, (Z)-enol esters underwent asymmetric epoxidation to
give the epoxides in high yields with high enantioselectivity ranging from 86 to >99% ee in the presence
of aqueous hydrogen peroxide as the stoichiometric oxidant. Complete enantioselectivity was observed
in the reaction of (Z)-3,3-dimethylbut-1-en-1-yl 4-methoxybenzoate. The obtained epoxide was readily
transformed into the corresponding 1,2-diol by reduction with lithium borohydride without erosion of
the high enantiomeric excess.
Received 30 April 2011
Accepted 8 June 2011
Available online 16 June 2011
This paper is dedicated to Professor Satoshi
ꢀ
Omura on the occasion of his receipt of the
Tetrahedron Prize for Creativity in Organic
Chemistry for 2010
Ó 2011 Elsevier Ltd. All rights reserved.
Keywords:
Asymmetric reaction
Epoxidation
Hydrogen peroxide
Titanium
Enol ester
1. Introduction
epoxidation of enol esters and ethers, in which enol esters and
ethers are transformed into the corresponding epoxides and
a-
Enantioenriched epoxides are one of the most versatile chiral
building blocks in organic transformations, and thus many efficient
asymmetric epoxidation methods using chiral transition metal-
based catalysts and organocatalysts have been developed in the
last three decades.1e3 Epoxides prepared from enol esters and
ethers are also synthetically useful compounds, because these ep-
hydroxy ketones with high enantioselectivity, respectively.5 In ad-
dition, Shi and co-workers demonstrated that enol ester epoxides
can rearrange to
a-acyloxy ketones in a highly stereoselective
manner.5c In this way, efficient epoxidation reactions of enol esters
and ethers have been reported and high enantioselectivity has been
achieved. However, no examples of asymmetric epoxidation of al-
dehyde enol esters and ethers have yet been reported.
oxides can be readily transformed into the corresponding
a-hy-
droxy carbonyl compounds and 1,2-diols, which are prevalent
structural motifs in natural products and biologically active com-
pounds.4e12 Thus, the development of asymmetric epoxidation of
enol esters and ethers has attracted attention. Chiral man-
ganese(salen) complexes can be applied to asymmetric epoxidation
of enol esters and ethers.4 For example, Fukuda and Katsuki
reported that cyclic enol ethers undergo enantioselective epoxi-
dation and subsequent epoxide ring opening in alcoholic solvent to
On the other hand, we have reported that Ti(salalen) complex 1 is
an effective catalyst for asymmetric epoxidation of various simple
olefins using aqueous hydrogen peroxide as the stoichiometric
oxidant.13,14 In particular, cis-disubstituted olefins exhibited high
reactivity and enantioselectivity. On the basis of our preceding
studies, we envisioned that the Ti(salalen) system shows high
enantioselectivity in the epoxidation of aldehyde enol esters, which
correspond to cis-disubstituted olefins. Here, we demonstrate highly
enantioselective epoxidation of aldehyde (Z)-enol esters (Scheme 1).
give a
-hydroxy acetals with high enantioselectivity.4c A fructose-
derived ketone catalyst also shows high enantioselectivity in the
2. Result and discussion
We first conducted asymmetric epoxidation of an E/Z mixture of
oct-1-enyl benzoate (E/Z¼4:5) with 2 mol % of Ti(salalen) complex
* Corresponding author. E-mail address: katsuscc@chem.kyushu-univ.jp
(T. Katsuki).
0040-4020/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2011.06.022

K. Matsumoto et al. / Tetrahedron 67 (2011) 6474e6478
6475
excess, the substitution with an electron-donating methoxy group
at the para-position slightly improved enantioselectivity (entries 2
and 3). Introduction of the ortho-methoxy group had no effect on
the enantioselectivity (entry 4). The reaction of 2,4-
dimethoxybenzoate also gave the epoxide 6 with 93% ee, but
lower epoxide yield was observed (entry 5). Aliphatic 3-
phenylpropanoate showed inferior reactivity and enantiose-
lectivity (entry 6). Consequently, we chose 4-methoxyphenyl ben-
zoate for further exploration. It is of note that no products other
than the desired epoxides were detected by 1H NMR analysis of the
crude reaction mixture.
Other (Z)-enol esters bearing a 4-methoxybenzoate group also
displayed high enantioselectivity in the titanium(salalen)-
catalyzed asymmetric epoxidation (Scheme 3). The enol ester
bearing an isobutyl group showed high enantioselectivity of 98%.
The reaction of cyclohexyl-substituted enol ester also furnished the
epoxide 9 with 98% ee. Excellent enantioselectivity of >99% ee was
observed with tert-butyl group. Irrespective of the steric hindrance,
the epoxide 10 was obtained in high yield.
O
O
Ti(salalen)
1
(2 mol%)
R1
R1
30% H2O2
O
R2
R2
CH2Cl2, 25°C
O
O
86->99% ee
H
N
N
O
Ti
O
Ph Ph
O
2
Ti(salalen)
1
Scheme 1. Ti(salalen)-catalyzed asymmetric epoxidation of (Z)-enol esters.
1 at 25 ꢀC (Scheme 2). As is the case with other olefin substrates in
Ti(salalen)-catalyzed asymmetric epoxidation, high reactivity, and
enantioselectivity were observed for (Z)-oct-1-enyl benzoate, and
the (E)-isomer gave poor yield and diminished enantioselectivity.
Thus, we focused on the asymmetric epoxidation of (Z)-enol esters,
which can be readily prepared in a highly stereoselective manner
by ruthenium-catalyzed anti-Markovnikov addition of carboxylic
acids to terminal alkynes reported by Goossen and co-workers.15
O
Ti(salalen) 1 (2 mol%)
30% H2O2
O
R
O
R
CH2Cl2, 25°C
O
O
8: 86%, 98% ee
R = 4-MeOC6H4
O
Ti(salalen) 1 (2 mol%)
30% H2O2
O
R
O
R
O
CH2Cl2, 25°C
Ti(salalen) 1 (2 mol%)
nC6H13
nC6H13
30% H2O2
O
O
O
Ph
O
Ph
9: 89%, 98% ee
CH2Cl2, 25°C
O
O
O
(E)-isomer: 19%, 71% ee
(Z)-isomer: >95%, 92% ee
E/Z = 4:5
Ti(salalen) 1 (2 mol%)
30% H2O2
O
R
O
R
Scheme 2. Asymmetric epoxidation of (Z)- and (E)-oct-1-enyl benzoate.
CH2Cl2, 25°C
O
O
The effect of the ester moiety on reactivity and enantiose-
lectivity was investigated in the reaction of (Z)-oct-1-enyl esters
(Table 1). The epoxidation of geometrically pure (Z)-oct-1-enyl
benzoate furnished the epoxide 2 in high yield with high enan-
tioselectivity of 92% ee (entry 1). The epoxidation proceeds in
a stereospecific manner, thus no trans-epoxide was observed.
While the introduction of an electron-withdrawing trifluoromethyl
group at the para-position resulted in loss of the enantiomeric
10: 90%, >99% ee
Scheme 3. Asymmetric epoxidation of aliphatic (Z)-enol esters.
Both aliphatic enol esters and aromatic esters underwent ep-
oxidation effectively (Scheme 4). While the reaction of (Z)-styryl
benzoate gave the epoxide with somewhat lower enantiomeric
excess of 86%, replacement of the benzoyl moiety with a 3-
phenylpropanoyl group led to the significant improvement of the
enantioselectivity to afford the epoxide 12 with 97% ee. It is of in-
terest that the ester moieties had the reverse effect on the asym-
metric induction in epoxidation of aromatic- and aliphatic-
substituted enol esters.
Table 1
Effect of ester moietya
O
Ti(salalen) 1 (2 mol%)
nC6H13
nC6H13
30% H2O2
O
R
O
R
CH2Cl2, 25°C
O
Ti(salalen) 1 (2 mol%)
O
O
Ph
Ph
2-7
30% H2O2
O
Ph
O
Ph
CH2Cl2, 25°C
Entry
R
Yield/%b
% eec
O
O
1
2
3
4
5
6
Ph (2)
4-CF3C6H4 (3)
4-MeOC6H4 (4)
2-MeOC6H4 (5)
2,4-(MeO)2C6H3 (6)
PhCH2CH2 (7)
>95 (94)
>95 (94)
>95 (91)
>95 (86)
82 (72)
92
87
93
92
93
63
11: 83%, 86% ee
O
Ti(salalen) 1 (2 mol%)
Ph
Ph
30% H2O2
36 (27)
O
CH2CH2Ph
O
CH2CH2Ph
CH2Cl2, 25°C
a
The reaction was carried out with enol ester (0.5 mmol), 30% H2O2 (0.6 mmol),
O
O
and Ti(salalen) complex (2 mol %) in CH2Cl2 at 25 ꢀC.
12: 78%, 97% ee
b
Determined by 1H NMR (400 MHz). The number in parentheses is isolated yield.
Determined by chiral HPLC analysis, see the Experimental section for details.
c
Scheme 4. Asymmetric epoxidation of aromatic (Z)-enol esters.

6476
K. Matsumoto et al. / Tetrahedron 67 (2011) 6474e6478
Kanto Chemical Co., Inc. and used as received. All enol esters were
The obtained epoxides could be transformed into useful com-
prepared by the procedure reported by Goossen co-workers.14
pounds without eroding enantiomeric excess. Reduction of epoxide
4 with lithium borohydride in diethyl ether afforded the corre-
sponding 1,2-diol 13 in high yield (Scheme 5).16 No decrease of the
high enantiomeric excess was observed during this transformation.
4.2. Asymmetric epoxidation: general procedure
To a solution of Ti(salalen) complex 1 (17.8 mg, 2 mol %) in
dichloromethane (0.5 mL) was added enol ester (0.5 mmol).
Aqueous hydrogen peroxide (61.9 mL) was added to the solution,
O
OH
and then the resulting mixture was stirred at 25 ꢀC. After 12 h, the
reaction was quenched with saturated Na2S2O3. The reaction mix-
ture was extracted with dichloromethane, and the extracts was
dried over anhydrous Na2SO4. The crude product was purified by
column chromatography on silica gel (n-hexane/ether) to give the
desired epoxide. The enantiomeric excess was determined by HPLC
analysis on a chiral stationary phase.
nC6H13
LiBH4
OH
O
R
nC6H13
13: 93%
Et2O, RT
O
R = 4-MeOC6H4
4: 93% ee
BzCl, Et3N
OBz
4.2.1. cis-3-Hexyloxiran-2-yl benzoate (2). Colorless oil; 116.5 mg,
94%; 92% ee (CHIRALPAK IC, n-hexane/i-PrOH 95/5); [a 19
]
ꢁ26.8 (c
OBz
D
nC6H13
1.50, CHCl3); FTIR (neat): 2926, 2855, 1732, 1601, 1583, 1454, 1375,
1315, 1263, 1177, 1094, 1069, 1026, 978, 831, 710, 687, 673,
14: 91%, 92% ee
536 cmꢁ1; 1H NMR (CDCl3):
d
8.04 (d, J¼7.3 Hz, 2H), 7.62e7.58 (m,
Scheme 5. Reduction of enol ester-derived epoxide 4 to 1,2-diol 13.
1H), 7.48e7.44 (m, 2H), 5.79 (d, J¼2.4 Hz, 1H), 3.10 (ddd, J¼2.4, 5.9,
6.3 Hz, 1H), 1.86e1.72 (m, 2H), 1.61e1.48 (m, 2H), 1.43e1.37 (m, 6H),
We further investigated asymmetric epoxidation of ketone enol
esters under the titanium-catalyzed conditions. Although cyclo-
pent-1-en-1-yl benzoate underwent epoxidation with good enan-
tioselectivity of 85%, a low yield of epoxide 15 was observed
(Scheme 6).5a,c
0.88 (t, J¼6.3 Hz, 3H) ppm; 13C NMR (CDCl3):
d 166.1, 133.6, 129.8,
129.1, 128.5, 76.5, 56.8, 31.6, 29.0, 27.0, 26.0, 22.5, 14.0 ppm; ele-
mental analysis: calcd (%) for C15H20O3: C 72.55, H 8.12; found: C
72.73, H 8.14.
4.2.2. cis-3-Hexyloxiran-2-yl 4-trifluoromethylbenzoate (3). Colorless
oil; 148 mg, 94%; 87% ee (CHIRALPAK IC, n-hexane/i-PrOH 95/5);
O
O
Ti(salalen) 1 (2 mol%)
a 19
]
ꢁ18.1 (c 2.29, CHCl3); FTIR (neat): 2930, 2912, 2856, 1746, 1514,
Ph
O
Ph
O
30% H2O2
[
D
O
1458, 1412, 1327, 1267, 1171, 1096, 1067, 1018, 862, 831, 773, 702,
CH2Cl2, 25°C
689 cmꢁ1; 1H NMR (CDCl3):
d
8.15 (d, J¼7.8 Hz, 2H), 7.74 (d, J¼7.8 Hz,
2H), 5.82 (d, J¼2.4 Hz,1H), 3.12 (ddd, J¼2.4, 5.9, 6.3 Hz,1H),1.86e1.71
15: 21%, 85% ee
Scheme 6. Asymmetric epoxidation of ketone enol esters.
(m, 2H), 1.64e1.26 (m, 8H), 0.88 (t, J¼6.3 Hz, 3H) ppm; 13C NMR
(CDCl3):
d
165.0, 135.1 (q, JCeF¼33 Hz), 132.3, 130.2, 125.6 (q,
JCeF¼3 Hz), 123.5 (q, JCeF¼273 Hz), 77.0, 56.8, 31.7, 29.0, 27.0, 26.0,
22.5, 14.0 ppm; elemental analysis: calcd (%) for C16H19F3O3: C 60.75,
H 6.05; found: C 60.90, H 6.12.
3. Conclusions
We have demonstrated that titanium(salalen) complex 1 effec-
tively catalyzes asymmetric epoxidation of aldehyde (Z)-enol esters
in the presence of aqueous hydrogen peroxide as the stoichiometric
oxidant. A range of (Z)-enol esters gave the epoxides in high yield
with high enantioselectivity ranging from 86 to >99% ee. Ketone
enol esters also underwent epoxidation with good enantiose-
lectivity albeit with low epoxide yield. The obtained epoxides were
transformed into the corresponding 1,2-diols with no erosion of
high enantiomeric excess.
4.2.3. cis-3-Hexyloxiran-2-yl 4-methoxybenzoate (4). Colorless oil;
127 mg, 91%; 93% ee (CHIRALPAK IC, n-hexane/i-PrOH 90/10);
[
a 19
]
ꢁ30.0 (c 2.20, CHCl3); FTIR (neat): 2932, 2909, 2856, 2841,
D
1728, 1607, 1582, 1512, 1460, 1421, 1317, 1256, 1169, 1090, 1028, 847,
768, 694, 611 cmꢁ1; 1H NMR (CDCl3):
d
7.99 (d, J¼8.8 Hz, 2H), 6.94
(d, J¼8.8 Hz, 2H), 5.77 (d, J¼2.4 Hz, 1H), 3.87 (s, 3H), 3.09 (ddd,
J¼2.4, 5.9, 6.3 Hz, 1H), 1.85e1.71 (m, 2H), 1.63e1.26 (m, 8H), 0.89 (t,
J¼6.3 Hz, 3H) ppm; 13C NMR (CDCl3):
d 166.1, 164.3, 132.2, 121.7,
114.1, 76.7, 57.1, 55.8, 32.0, 29.3, 27.4, 26.3, 22.8, 14.3 ppm; ele-
mental analysis: calcd (%) for C16H22O4: C 69.04, H 7.97; found: C
69.02, H 7.97.
4. Experimental section
4.1. General
4.2.4. cis-3-Hexyloxiran-2-yl 2-methoxybenzoate (5). Colorless oil;
120 mg, 86%; 92% ee (CHIRALPAK AD-H, n-hexane/i-PrOH 99/1);
All reactions were carried out in an oven-dried glassware with
magnetic stirring under air. 1H and 13C NMR spectra were measured
on a JEOL AL-400 spectrometer. Tetramethylsilane (TMS) served as
internal standard (0 ppm) for 1H NMR and CDCl3 was used as in-
ternal standard (77.0 ppm) for 13C NMR. Optical rotations were
measured on a JASCO P-1020 polarimeter. Infrared spectra were
measured using disposal polyethylene or polytetrafluoroethylene
IR cards on a SHIMADZU FTIR-8600 spectrophotometer. High-
performance liquid chromatography was carried out using SHI-
MADZU LC-10AT-VP equipped with a variable wavelength detector
on chiral stationary columns from Daicel Chemical Industries, Ltd.
Hydrogen peroxide (30%, Cat. No. 18084-00) was purchased from
[
a
]
20 ꢁ23.0 (c 1.16, CHCl3); FTIR (neat): 2932, 2908, 2856,1717, 1601,
D
1582, 1491, 1466, 1437, 1375, 1298, 1238, 1128, 1051, 1024, 976, 870,
833, 756, 702, 660 cmꢁ1; 1H NMR (CDCl3):
d
7.84 (dd, J¼1.5, 7.8 Hz,
1H), 7.54e7.49 (m, 1H), 7.01e6.97 (m, 2H), 5.78 (d, J¼2.4 Hz, 1H),
3.91 (s, 3H), 3.08 (ddd, J¼2.4, 5.9, 6.3 Hz, 1H), 1.86e1.70 (m, 2H),
1.61e1.26 (m, 8H), 0.88 (t, J¼6.8 Hz, 3H) ppm; 13C NMR (CDCl3):
d
165.8, 160.1, 134.7, 132.4, 120.4, 118.8, 112.4, 76.7, 57.1, 56.2, 32.0,
29.4, 27.3, 26.3, 22.8, 14.3 ppm; elemental analysis: calcd (%) for
C16H22O4: C 69.04, H 7.97; found: C 69.10, H 7.95.
4.2.5. cis-3-Hexyloxiran-2-yl 2,4-dimethoxybenzoate (6). White
solid; 111 mg, 72%; 93% ee (CHIRALPAK AD-3, n-hexane/i-PrOH 95/

K. Matsumoto et al. / Tetrahedron 67 (2011) 6474e6478
6477
21
5); [
1574, 1505, 1462, 1418, 1373, 1213, 1136, 1105, 1069, 1030, 928, 835,
768, 729, 696 cmꢁ1 1H NMR (CDCl3):
a
]
ꢁ28.1 (c 2.06, CHCl3); FTIR (KBr): 2910, 2845, 1711, 1609,
[
a
]
21 þ18.0 (c 1.02, CHCl3); FTIR (neat): 3028, 2924,1755,1497,1454,
D
D
1416, 1352, 1134, 1078, 897, 872, 754, 698, 567 cmꢁ1
;
1H NMR
;
d
7.87 (d, J¼8.3 Hz, 1H),
(CDCl3): d 7.35e7.32 (m, 5H), 7.27e7.23 (m, 2H), 7.19e7.16 (m, 1H),
6.52e6.48 (m, 2H), 5.76 (d, J¼2.4 Hz, 1H), 3.89 (s, 3H), 2.86 (s, 3H),
7.08e7.06 (m, 2H), 5.73 (d, J¼2.4 Hz,1H), 4.04 (d, J¼2.4 Hz,1H), 2.80
3.06 (ddd, J¼2.4, 5.9, 6.3 Hz, 1H), 1.85e1.70 (m, 2H), 1.61e1.26 (m,
(t, J¼7.81 Hz, 2H), 2.61e2.47 (m, 2H) ppm; 13C NMR (CDCl3):
d 172.3,
8H), 0.88 (t, J¼6.8, 3H) ppm; 13C NMR (CDCl3):
d
165.0, 164.9, 162.1,
139.8, 132.4, 128.5, 128.4, 128.1, 128.0, 127.2, 126.3, 76.8, 57.2, 35.5,
30.3 ppm; elemental analysis: calcd (%) for C17H16O3: C 76.10, H
6.01; found: C 76.20, H 5.92.
134.3, 110.9, 104.7, 98.9, 76.1, 56.8, 55.9, 55.5, 31.7, 29.1, 27.1, 26.0,
22.5, 14.0 ppm; elemental analysis: calcd (%) for C17H24O5: C 66.21,
H 7.84; found: C 66.25, H 7.64.
4.2.12. 6-Oxabicyclo[3.1.0]hexan-1-yl benzoate (15). Colorless oil;
21%, 85% ee (DAICEL CHIRALPAK AD-H, n-hexane/i-PrOH 99:1);
4.2.6. cis-3-Hexyloxiran-2-yl 3-phenylpropanoate (7). Colorless oil;
20 ꢁ29.5 (c 0.66, CHCl3) [lit.5c
[a]
25 ꢁ26.8 (c 0.41, CHCl3), 80% ee];
20
[a]
D
D
37 mg, 27%; 63% ee (CHIRALPAK IC, n-hexane/i-PrOH 90/10); [a]
D
FTIR (neat): 2937, 2855,1730,1601,1421,1275,1252,1202,1067,1024,
ꢁ13.1 (c 0.62, CHCl3); FTIR (neat): 2910, 2856, 1757, 1497, 1454,
1358, 1136, 1109, 750, 700 cmꢁ1 1H NMR (CDCl3):
7.31e7.19 (m,
941, 903, 708 cmꢁ1; 1H NMR (400 MHz, CDCl3):
d 8.06e8.04 (m, 2H),
;
d
7.61e7.57 (m, 1H), 7.47e7.43 (m, 2H), 3.80 (s, 1H), 2.46 (dd, J¼8.8,
5H), 5.55 (d, J¼2.4, 1H), 2.99e2.95 (m, 3H), 2.73e2.69 (m, 2H),
1.68e1.24 (m, 10H), 0.89 (t, J¼6.3 Hz, 3H) ppm; 13C NMR (CDCl3):
13.2 Hz,1H), 2.18e2.10 (m,1H), 2.01e1.88 (m, 2H),1.81e1.73 (m,1H),
1.62e1.52 ppm (m, 1H); 13C NMR (100 MHz, CDCl3):
d 165.0, 133.6,
d
172.6, 140.0, 128.5, 128.2, 126.4, 76.1, 56.6, 35.7, 31.6, 30.5, 29.0,
129.9, 129.2, 128.5, 89.8, 62.6, 28.2, 26.0, 20.0 ppm; elemental anal-
ysis: calcd (%) for C12H12O3:C 70.57, H 5.92; found: C 70.51, H 6.00.
26.8, 25.9, 22.5, 14.0 ppm; elemental analysis: calcd (%) for;
C17H24O3: C 73.88, H 8.75; found: C 74.04, H 8.78.
4.3. Reduction of epoxide 4
4.2.7. cis-3-Isobutyloxiran-2-yl 4-methoxybenzoate (8). Colorless
oil; 107 mg, 86%, 98% ee (DAICEL CHIRALPAK IC, hexane/i-PrOH
20
To a solution of epoxide 4 (100.0 mg) in diethyl ether (3.0 mL)
was added lithium borohydride (23.5 mg) at 0 ꢀC and the resulting
mixture was stirred at room temperature. After 30 min, the reaction
was quenched with saturated NH4Cl aq. The reaction mixture was
extracted with ether, and the extracts were washed with water and
brine and then dried over anhydrous Na2SO4. The crude product
was purified by column chromatography on basic silica gel (n-
hexane/ether¼4:1) to give the 1,2-diol 13 (48.9 mg, 93%). To a so-
lution of diol 13 (30.0 mg) in CH2Cl2 (1.0 mL) was added triethyl-
80:20); [
a
]
ꢁ28.6 (c 2.43, CHCl3); FTIR (neat): 2957, 1730, 1605,
D
1512, 1466, 1317, 1261, 1165, 1142, 1099, 1024, 843, 770 cmꢁ1
;
1H
NMR (400 MHz, CDCl3): 8.01e7.97 (m, 2H), 6.96e6.92 (m, 2H),
d
5.77 (d, J¼2.4, 1H), 3.87 (s, 3H), 3.14e3.10 (m, 1H), 1.96e1.86 (m,
1H), 1.75e1.61 (m, 2H), 1.03 (d, J¼6.8 Hz, 3H), 1.02 ppm (d, J¼6.8 Hz,
3H); 13C NMR (100 MHz, CDCl3):
d 165.8, 163.9, 131.9, 121.4, 113.8,
76.1, 55.7, 55.4, 35.7, 26.3, 22.8, 22.4 ppm; elemental analysis: calcd
(%) for C14H18O4:C 67.18, H 7.25; found: C 67.13, H 7.25.
amine (85.4
mL) and benzoylchloride (72.6 mL). After stirring
4.2.8. cis-3-Cyclohexyloxiran-2-yl 4-methoxybenzoate (9). Colorless
oil; 123 mg, 89%; 98% ee (CHIRALPAK IC, n-hexane/i-PrOH 80/20);
overnight, the reaction was quenched with saturated NaHCO3 aq.
The reaction mixture was extracted with CH2Cl2, and the extracts
were washed with brine and then dried over anhydrous Na2SO4.
The crude product was purified by column chromatography on
basic silica gel (n-hexane/ether¼20:1) to give the dibenzoate 14
(66.2 mg, 91%); 92% ee (CHIRALPAK AD-H, n-hexane/i-PrOH 99/1);
[
a]
20 ꢁ31.5 (c 1.60, CHCl3); FTIR (neat): 2910, 2857, 1726, 1607, 1582,
D
1512, 1450, 1421, 1252, 1169, 1094, 1028, 970, 879, 831, 799, 768,
696, 613, 554, 509 cmꢁ1 1H NMR (CDCl3):
; d 7.99e7.96 (m, 2H),
6.96e6.92 (m, 2H), 5.78 (d, J¼2.4 Hz, 1H), 3.87 (s, 3H), 2.81 (dd,
J¼2.4, 8.8 Hz, 1H), 2.03e2.01 (m, 1H), 1.77e1.55 (m, 5H), 1.36e1.11
[
a
]
25 þ4.97 (c 0.71, CHCl3) [lit.17
[
a
]
D
24 þ5.4 (c 0.63, CHCl3), >99% ee];
(m, 5H) ppm; 13C NMR (CDCl3):
d 166.2, 164.3, 132.2, 121.7, 114.1,
D
FTIR (neat): 2920, 2851, 1715, 1684, 1649, 1583, 1458, 1261, 1177,
76.7, 60.9, 55.8, 36.5, 30.6, 28.9, 26.5, 25.8, 25.6 ppm; elemental
analysis: calcd (%) for C16H20O4: C 69.54, H 7.30; found: C 69.80,
H 7.28.
1069, 1026, 849, 716, 689 cmꢁ1 1H NMR (CDCl3):
; d 8.06e8.00 (m,
4H), 7.57e7.52 (m, 2H), 7.45e7.39 (m, 4H), 5.53e5.47 (m, 1H), 4.56
(dd, J¼3.4, 11.7 Hz, 1H), 4.47 (dd, J¼6.3, 11.7 Hz, 1H), 1.89e1.74 (m,
2H), 1.52e1.26 (m, 8H), 0.87 (t, J¼6.8 Hz, 3H) ppm; 13C NMR
4.2.9. cis-3-tert-Butyloxiran-2-yl 4-methoxybenzoate (10). Colorless
oil; 113 mg, 90%; >99% ee (CHIRALPAK IC, n-hexane/i-PrOH 80/20);
(CDCl3):
d 166.3, 166.1, 133.0, 133.0, 130.2, 129.9, 129.7, 128.4, 72.2,
65.7, 31.6, 31.0, 29.1, 25.1, 22.5, 14.0 ppm; elemental analysis: calcd
(%) for C22H26O4: C 74.55, H 7.39; found: C 74.48, H 7.32.
[
a
]
19 ꢁ26.3 (c 1.89, CHCl3); FTIR (neat): 2950, 1728, 1607, 1582, 1512,
D
1421, 1367, 1256, 1090, 1007, 959, 930, 847, 806, 768, 696, 617,
554 cmꢁ1
2H), 5.72 (d, J¼2.4 Hz, 1H), 3.87 (s, 3H), 2.81 (d, J¼2.4, 1H), 1.13 (s,
9H) ppm; 13C NMR (CDCl3):
165.9, 164.0, 131.9, 121.4, 113.9, 77.6,
; d 8.00e7.96 (m, 2H), 6.96e6.92 (m,
1H NMR (CDCl3):
Acknowledgements
d
We are grateful to Nissan Chemical Industries and the Global
COE program ‘Science for Future Molecular Systems’ from MEXT
(Japan) for generous financial support. T.O. is grateful for JSPS Re-
search Fellowship for Young Scientists.
64.0, 55.5, 31.2, 27.3 ppm; elemental analysis: calcd (%) for
C14H18O4: C 67.18, H 7.25; found: C 67.19, H 7.23.
4.2.10. cis-3-Phenyloxiran-2-yl benzoate (11). Colorless oil; 100 mg,
83%; 86% ee (CHIRALPAK IC, n-hexane/i-PrOH 95/5); [
a
]
21 þ42.5 (c
D
References and notes
1.15, CHCl3); FTIR (neat): 2924, 2852, 1734, 1601, 1495, 1454, 1360,
1315, 1252, 1205, 1177, 1094, 1069, 1026, 904, 862, 756, 710, 583,
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