Asymmetric reduction of aliphatic ketones and acyl silanes using chiral anti-pentane-2,4-diol and a catalytic amount of 2,4-dinitrobenzenesulfonic acid

Article abstract of DOI:10.1016/j.tet.2010.06.012

Aliphatic ketones were reduced to the corresponding secondary alcohols by using anti-1,3-diol and a catalytic amount of 2,4-dinitrobenzenesulfonic acid (DNBSA) in benzene at reflux. Addition of 1-octanethiol in that media improved the efficiency of the reduction. Asymmetric reduction of aliphatic ketones was performed by using chiral anti-pentane-2,4-diol, and highly asymmetric induction (up to >99% ee) was observed in the reduction of tert-alkyl ketones. Asymmetric reduction of acyl silanes using chiral anti-pentane-2,4-diol and DNBSA proceeded efficiently in the absence of octanethiol and the corresponding α-silyl alcohols were obtained in high yields with high ees.

Full text of DOI:10.1016/j.tet.2010.06.012

Tetrahedron 66 (2010) 6062e6069
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Tetrahedron
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Asymmetric reduction of aliphatic ketones and acyl silanes using chiral anti-
pentane-2,4-diol and a catalytic amount of 2,4-dinitrobenzenesulfonic acid
*
Jun-ichi Matsuo , Yu Hattori, Mio Hashizume, Hiroyuki Ishibashi
School of Pharmaceutical Sciences, Institute of Medical, Pharmaceutical and Health Sciences, Kanazawa University, Kakuma-machi, Kanazawa 920-1192, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 10 May 2010
Received in revised form 3 June 2010
Accepted 4 June 2010
Available online 10 June 2010
Aliphatic ketones were reduced to the corresponding secondary alcohols by using anti-1,3-diol and
a catalytic amount of 2,4-dinitrobenzenesulfonic acid (DNBSA) in benzene at reflux. Addition of 1-oc-
tanethiol in that media improved the efficiency of the reduction. Asymmetric reduction of aliphatic
ketones was performed by using chiral anti-pentane-2,4-diol, and highly asymmetric induction (up to
>99% ee) was observed in the reduction of tert-alkyl ketones. Asymmetric reduction of acyl silanes using
chiral anti-pentane-2,4-diol and DNBSA proceeded efficiently in the absence of octanethiol and the
Keywords:
Asymmetric reduction
Ketone
corresponding
a
-silyl alcohols were obtained in high yields with high ees.
Ó 2010 Elsevier Ltd. All rights reserved.
Acyl silane
MeerweinePonndorfeVerley reduction
Oppenauer oxidation
1. Introduction
Table 1
Brønsted acid-controlled selectivity between acetalization and reduction of ketone 1
with diol 2
MeerweinePonndorfeVerley (MPV) reduction of ketone has
distinguishing usefulness in organic synthesis.1 A stoichiometric
amount of metal alkoxides (usually aluminum triisopropoxide) is
usually employed as a reducing agent, and the metal part plays an
important role in the MPV reduction: it activates the carbonyl
group of ketones to be reduced and promotes hydride transfer from
the CeH bond of the alkoxide. Though extensive efforts have been
made to develop a catalytic method of MPV reduction,2,3 there
had been no report of metal-free MPV reduction of ketone with
alcohol until our previous brief report.4 We report here details
of asymmetric reduction of ketones and acyl silanes that uses
chiral anti-pentane-2,4-diol and a catalytic amount of a strong
Brønsted acid.
In the course of our study on stereoselective reduction of 24-oxo-
choresterol derivatives,5 we planned aluminum hydride-promoted
ring cleavage of chiral acetal 3.6 We attempted to prepare chiral acetal 3
from ketone 1 and chiral diol 2 by using a catalytic amount (5 mol %) of
pyridinium p-toluenesulfonate (PPTS) in benzene at reflux with con-
tinuous removal of water (Table 1). However, the desired acetal 3 was
obtained in only 8% yield, probably due to steric hindrance around the
carbonyl group of ketone 1(entry 1).7 The use of p-toluenesulfonic acid
(TsOH) instead of PPTS gave acetal 3 also in low (12%) yield, but alcohol
Entry
Catalyst
Time (h)
3 (% yielda)
4 (% yielda)
1
2
3
PPTS
34
6
2
8
12
0
0
4
TsOH
DNBSAb
23c
a
Isolated yield.
2,4-Dinitrobenzenesulfonic acid.
24-R/S¼88.5:11.5.
b
c
2,4-dinitrobenzenesulfonic acid (DNBSA), a stronger Brønsted acid
than TsOH, was employed, acetal 3 was not formed at all, but alcohol 4
was obtained in 23% yield (entry 3). Moreover, stereoselectivity for
this reduction (24-R/S¼88.5:11.5) was higher than that for
CoreyeShibataeBakshi (CBS) reduction8 (24-R/S¼76:24,5 Scheme 1).
4
was surprisingly obtained in 4% yield (entry 2). When
* Corresponding author. E-mail address: jimatsuo@p.kanazawa-u.ac.jp (J. Matsuo).
0040-4020/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2010.06.012

J.-ichi Matsuo et al. / Tetrahedron 66 (2010) 6062e6069
6063
Table 3
Effects of solvents in reduction of ketone 5 to alcohol 6 with diol 2a
Entry
Solvent
Time (h)
Isolated yield (%)
1
2
3
4
Benzene
Toluene
CCl4
4
1
5
1
13
4
5
ClCH2CH2Cl
9
a
Ketone 5 (1.0 equiv), diol 2 (1.1 equiv), and DNBSA (5 mol %) were used. Re-
actions were carried out at reflux. In all cases, optical purity of 6 was >99% ee, which
was determined by chiral HPLC.
Scheme 1. CBS reduction of 1.
Various diols were employed in reduction of methyl ketone 7 to
alcohol 8 in order to clarify what structural feature of diol was re-
quired for the DNBSA-reduction of ketone (Table 4). The effect of
methyl groups of diol 2 was first examined by using (3R)-butan-1,3-
2. Results and discussion
2.1. Asymmetric reduction of ketones
Various Brønsted acids were further tested for the reaction of
ketone 5 with chiral diol 2 in order to find an appropriate Brønsted
acidcatalystforthereductionofketones (Table 2). Inreductionof tert-
butyl ketone 5, trifluoroacetic acid (TFA) and TsOH did not work as
catalysts(entries1and2), thoughtheuseofTsOHgavealcohol 4inthe
reduction of isopropyl ketone 1 (Table 1, entry 2). The steric hindrance
of tert-butyl ketone 5 retarded the reduction with 2. The use of
stronger Brønsted acids such as 2-fluorobenzenesulfonic acid (FBSA)9
and 4-nitrobenzenesulfonic acid (NBSA)10 gave alcohol 6 in 4% and 3%
yields, respectively, while the use of 2,4-dinitrobenzenesulfonic acid
(DNBSA)11 and trifluoromethanesulfonic acid(TfOH)gave alcohol 6 in
13% and 11% yields, respectively (entries 3e5 and 7). Thus, a strong
Brønsted acid worked as an effective catalyst for the present re-
duction, and DNBSA was found to be an appropriate Brønsted acid
catalyst. Increasing the amount of DNBSA from 5 to 20 mol % resulted
in rapid disappearance of diol 2 and lowered the yield of 6, probably
because acid-catalyzed dehydration of 6 took place (entry 6). Ace-
talization of tert-butyl ketone 5 with diol 2 was not observed with any
of the Brønsted acids shown in Table 2. In all of the cases described
above, optical purity of the reduction product 6 was >99% ee (R), and
the enantioselectivity did not depend on the Brønsted acid employed.
Table 4
Effects of diols in DNBSA-catalyzed reduction of ketone 7 to alcohol 8 in benzene at
reflux
Entry
1
Diol
Time (h)
3
8 (% Yield)a
27b
2
3
4
5
6
7
2
4c
2
9
Table 2
Effects of Brønsted acids in reduction of ketone 5 to alcohol 6 with diol 2
2
Traced
Tracee
0
0.5
2
Entry
Brønsted acida
Time (h)
Isolated yield (%)
1
2
3
4
TFA
TsOH
FBSA
NBSA
DNBSA
DNBSA
TfOH
2
18
5.5
4
4
1.5
2
0
Trace
4
3
13
6
11
2
0f
5
6b
7
a
TFA: trifluoroacetic acid; TsOH: p-toluenesulfonic acid; FBSA: 2-fluo-
robenzenesulfonic acid; NBSA: 4-nitrobenzenesulfonic acid; DNBSA: 2,4-dini-
trobenzenesulfonic acid; TfOH: trifluoromethanesulfonic acid.
8
2
41
b
DNBSA (20 mol %) was used.
15a: R¼Et
9
15b: R¼i-Pr
15c: R¼t-Bu
15d: R¼i-Bu
15e: R¼Ph
2
3
1
1.5
46
10
11
12
18
28g
Trace
Next, the reduction of ketone 5 with diol 2 was carried out in
various solvents at reflux (Table 3). The reduction of 5 in toluene
gave alcohol 6 in 4% yield (entry 2), and the use of halogenated
hydrocarbons such as carbon tetrachloride and dichloroethane
gave alcohol 6 in low yields (entries 3 and 4). Reduction in other
polar solvents such as THF, diisopropyl ether, ethanol, and aceto-
nitrile did not give 6. Therefore, benzene was found to be the most
suitable solvent for the present reduction.
a
Isolated yield.
b
c
d
e
f
48% ee (R).
ee was not determined.
Compound 16 was isolated in 55% yield (dr¼61:39).
Compound 17 was isolated in 56% yield.
Compound 18 was isolated in 32% yield
g
Compound 19 was isolated in 18% yield (based on 7).

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J.-ichi Matsuo et al. / Tetrahedron 66 (2010) 6062e6069
diol (9) and propane-1,3-diol (10). It was found that lack of the
methyl substituent of 2 significantly decreased the yield of re-
duction product 8 from 27% to 4e9% (entries 1e3). It was noted that
even diol 10 reduced ketone 7 by the catalysis of DNBSA. With
regard to the stereochemistry of 1,3-diol, anti-configuration was
critical for the present reduction because syn-1,3-diol 11 gave the
reduction product 8 in a trace amount but gave acetal 16 in 55%
yield (entry 4). Also, the use of anti-1,2-diol 12 and anti-1,4-diol 13
did not give reduction product 8, suggesting that the two hydroxy
groups of diol had to be positioned at the 1,3-position (entries 5 and
6). Therefore, anti-1,3-diol structure was found to be required for
effective reduction of ketone. The use of (ꢀ)-anti-diol 14, which did
not have any hydrogens at its 3-position, did not give reduction
Various thiols 28aee were used for DNBSA-catalyzed reduction of
ketone 7 with diol 2 in order to improve the efficiency of the reduction
(Table 5). It was found that addition of aromatic thiols, such as ben-
zenethiol 28a, o-methylbenzenethiol 28b, and p-methoxy-
benzenethiol 28c improved the yield of alcohol 8(entries 2e4). Further
improvement was observed when aliphatic thiols were used: octane-
thiol 28d and 2-ethylhexanethiol 28e gave alcohol 8 in 62% and 61%
yields, respectively (entries 5 and 6). Increasing the amount of diol 2
from 1.1 to 2.0 equiv did not change the efficiency of the reduction
(compare entry 5 with entry 7.). b-Arylthio or b-alkylthio pentan-2-
ones 29aee, which were formed by conjugate addition of thiol to in
situ-formed enone, were isolated in all cases. However, alcohols 30aee,
which were formed by reduction of 29aee with diol 2, were also
obtained. These results suggested that DNBSA-catalyzed reduction of
ketone 7 with diol 2 was improved by adding octanethiol, but con-
sumption of diol 2, which resulted from competitive reduction of
ketone 29, was not inhibited.
product 8 but afforded b-alkoxy ketone 18 in 32% yield (entry 7).
Table 5
Effects of thiols 28aee in DNBSA-catalyzed reduction of ketone 7 to alcohol 8 in
benzene at reflux
anti-1,3-Diols (ꢀ)-15aee having various substituents at their 1,3-
positionwere next employed. It was found that as the steric bulkiness
increased from methyl to isopropyl groups, the yield of alcohol 8 in-
creased, whereas substitution with a tert-butyl group decreased the
yield of 8 (entries 8e10). The use ofdiol15d (R¼i-Bu) resulted inrapid
disappearance of 15d and the yield of 8 was not improved compared
to that in the case of diol 2. In this case, enone 19 was isolated in 18%
yield (entry 11). A diol having a phenyl group (15e) did not catalyze
the reduction of 7. Before reduction of 7, dehydration of benzylic al-
cohol 15e might proceed under acidic conditions (entry 12).
Entry
Thiol
28
Time (h)
8a
29a
30a
A plausible mechanism for reduction of ketone 20 with diol 15 by
catalysis with DNBSA is shown in Scheme 2. Ketone 20 reacts with
anti-1,3-diol 15 in the presence of Brønstedacidto give oxocarbenium
ion (21 or 22). Acetal 24 can be formed via oxocarbenium ion 22,12 but
DNBSA, a strong Brønsted acid, catalyzes stereoselective cleavage13 of
the acetal ring of 24 to regenerate oxocarbenium ion 22. Oxocarbe-
niumion 21, which has twoR groups inequatorial positions, isformed
by CeC bond rotation in oxocarbenium ion 22. Then 1,5-hydride
transfer14 proceeds via a six-membered transition state shown in 21
1
2
3
4
None
PhSH
3
3
27
40
50
50
62
61
62
d
d
5
9
12
16
15
24
28a
28b
28c
28d
28e
28d
18
44
56
55
55
61
o-MeC6H4SH
p-MeOC6H4SH
C8H17SH
BuCHEtCH2SH
C8H17SH
2.5
2.5
3.5
2.5
3
5
6
7b
a
Isolated yield (%) based on 7.
Two equivalents of diol 2 were employed.
b
Effects of substituents of diol 15 bearing ethyl, propyl, isopropyl,
to form b-alkoxy ketone 23. Thus, intramolecular MPV reduction and
Oppenauer oxidation15 proceed in this step. Alcohol 25 and enone 26
are formed from 23 by Brønsted acid-catalyzed elimination. The in-
and isobutyl groups as the R group in the reduction of ketone 7 were
investigated again in the presence of octanethiol (Table 6). Compared
withdiol2, theuseof15a (R¼Et) and 15b (R¼i-Pr)didnotimprovethe
yield of alcohol 8 (entries 1, 2, and 4), though diols 15a and 15b clearly
improved the efficiency of the reduction in the absence of octanethiol
(Table 4, entries 8 and 9). When sterically hindered diol 15b was
volvement of b-alkoxy ketone 23 and enone 26 was confirmed by
isolation of compounds 18 and 19, respectively.
Table 6
Effects of diol 15 in DNBSA-catalyzed reduction of ketone 7 to alcohol 8 in the
presence of octanethiol
Scheme 2. Plausible mechanism for DNBSA-catalyzed reduction of ketone 20 to
alcohol 25 using anti-1,3-diol 15.
Competitive reduction of enone 26 with diol 15 was thought to
be the main reason for the low efficiency in DNBSA-catalyzed re-
duction of ketone 20 with diol 15.16 The improved efficiency in the
reduction with diol 15b (R¼i-Pr) was attributed to slow reduction
of sterically demanding enone 26b (R¼i-Pr). It was then expected
that addition of thiol to enone 26 would give 27, which was less
reactive for the reduction with diol 15 compared with enone 26.
Entry
Diol (R)
Time (h)
8a
31a
32a
1
2
3
4
5
2 (Me)
15a (Et)
15f (n-Pr)
15b (i-Pr)
15d (i-Bu)
3.5
1.5
1.5
1
62
64
62
50
54
55
52
52
32
29
16
7
6
0
0
2
a
Isolated yield (%) based on 7.

J.-ichi Matsuo et al. / Tetrahedron 66 (2010) 6062e6069
6065
Table 7
employed, the addition of octanethiol to in situ-formed enone took
place slowly to afford the corresponding -octylthio ketone 31b in
Asymmetric reduction of various ketones 33 using diol 2 and DNBSAa
b
Entry
Ketone
Product Yieldb (%) eec (%)
32% yield, which was lower than that in the case of diol 2 (55%) (en-
tries 1 and 4). Insufficient trapping of enone with octanethiol might
cause the undesired reduction of enone with diol, which was the
reason why further improvement was not observed when sterically
demanding diols were employed in the presence of octanethiol.
Therefore, the combination of octanethiol and diol 2, which is com-
mercially available as a chiral compound, was employed in the fol-
lowing experiments as optimized conditions.
The scope and limitations of DNBSA-catalyzed asymmetric re-
duction of ketones 33 with chiral diol 2 were investigated by using
octanethiol as an additive (Table 7). Reduction of tert-alkyl ketones such
as 33a,b and 5 proceeded with high asymmetric induction (99e>99% ee)
in 18e36% yields (entries 1e3). Reduction of sec-alkyl methyl ketones
31cef proceeded to give the corresponding alcohols 34cef in 42e57%
yields with 82e93% ees (entries 4e7), while reduction of isopropyl
ketones 33g and 1 proceeded in low yields with moderate selectivities
(entries 8 and 9). The steric hindrance around the carbonyl group of 33g
and 1, which was increased by substitution with a longer alkyl chain
than the methyl group of 33cef, wasthereasonforthelowyieldsof34g
and 4. Reduction of n-alkyl methyl ketones 33hejproceeded in 50e64%
yields and with about 50% ees (entries 10e12). In reduction of aromatic
ketone, acetophenone 33k did not give the desired alcohol 34k (entry
13). Detection of styrene by TLC analysis suggested that dehydration of
the formed benzylic alcohol 34k with DNBSA took place.
1
34a
6
18c
21d
>99
>99
2
3
4
5
34b
34c
34d
36
57
52
99
93
87
6
34e
50
82
2.2. Asymmetric reduction of acyl silanes
a
-Hydoxy silanes are useful building blocks in organic synthe-
sis.17 Optically active hydroxy silanes have been employed as
7
8
34f
42
82
66
a chiral auxiliary for oxocarbenium ion,18 and they have been used
for the synthesis of chiral alcohol by rearrangement of a-acetoxy
silane.19 The present method for reduction of ketone with chiral
alcohol 2 was applied to asymmetric reduction20 of acyl silanes21
34g
26d
for synthesis of optically active
Attempted reduction of acyl silane 35 by using diol 2 and DNBSA
in the presence of octanethiol did not give the desired -hydroxy
a-hydroxy silanes.
a
silane 36 at all, and alkenyl sulfide 37 was obtained in 25% yield (Eq.
1). The formation of alkenyl sulfide by the reaction of acyl silane and
thiol has already been reported,22 and this result suggested that the
reaction of acyl silane 35 and octhanethiol took place preferentially
compared to the reduction of acyl silane 35 with diol 2. Therefore,
the reduction of 35 with diol 2 was carried out in the absence of
octanethiol. It was surprisingly found that the reduction of 35 pro-
9
4
24d
24-R/S¼88:12
10
34h
50
51
ceeded verysmoothlytoafford a-hydroxysilane 34 in 83% yield with
high enantioselectivity (98% ee (R), Eq. 2). This result suggested that
the reduction of acyl silane 35 with diol 2 proceeded more rapidly
than the reactionwith pent-3-en-2-one, which is formed from diol 2
(see Scheme 2). The high reactivity of acyl silane can be ascribed to
its higher HOMO level, which is caused by interaction of the CeSi
bond (sCeSi) with lone pair electrons of the carbonyl group (no).23
11
12
34i
34j
60
64
52
51
Asymmetric reduction of various acyl silanes 38 was performed
by using chiral diol 2 and a catalytic amount of DNBSA in benzene at
reflux (Table 8). Asymmetric reduction of octanoyl silanes 38aec
bearing a trimethylsilyl, tert-butyldimethylsilyl, or dimethylphe-
nylsilyl group proceeded smoothly to afford the corresponding
13
34k
0
d
a
Ketone (1.0 equiv), diol 2 (1.1 equiv), C8H17SH (1.1 equiv), and DNBSA (5 mol %)
were refluxed in benzene using a DeaneStark apparatus.
a
-hydroxy silanes 39aec in good yields with high enantiose-
lectivities (entries 1e3). It was noted that asymmetric reduction of
acetyl silane 38d proceeded within 5 min, and alcohol 38d was
obtained in 85% yield with 95% ee (entry 5), while prolonged re-
action time (10 min) resulted in 77% yield of 39d with 75% ee. Thus,
b
Determined by 1H NMR analysis using an internal standard.
Determined by chiral HPLC (see Experimental section).
Isolated yield.
c
d
the formed
the reaction time, and partial racemization took place. Reduction of
-branched acyl silane 38e.proceeded in 55% yield with 97% ee
a
-hydroxy silane 39d was decomposed by extending
(entry 5), but the reduction of
proceed (entry 6). Reduction of enoyl silane 38g did not give the
desired -hydroxy silane 39g, probably due to dehydration of 39g
a-branced acyl silane 38f did not
b
a

6066
J.-ichi Matsuo et al. / Tetrahedron 66 (2010) 6062e6069
and diol 2 proceeded efficiently in the absence of octanethiol.
Highly asymmetric induction was observed when two substituents
attached on the carbonyl group of ketone and acyl silane were
sterically well-differentiated, and reduction of ketones and acyl
silanes bearing less-hindered substituents proceeded more
smoothly. It is generally believed that Brønsted acid-catalyzed re-
action of ketone and 1,3-diol gives the corresponding acetal, but the
present findings show that reduction can take place when a strong
Brønsted acid and some anti-1,3-diols are employed.
4. Experimental section
4.1. General
All melting points were determined on a Yanagimoto micro
melting point apparatus and are uncorrected. Infrared (IR) spectra
were recorded on a Shimadzu FTIRe8100. 1H NMR spectra were
recorded on a JEOL JNM EX270 (270 MHz), JEOL JNM ECS400
(400 MHz), JEOL JNM GSX500 (500 MHz), or JEOL JNM ECA600
Table 8
Asymmetric reduction of various acyl silanes 38 using diol 2 and DNBSAa
(600 MHz) spectrometer; chemical shifts (d) are reported in parts
Entry
Acyl silanes 38
Time
(min)
Product 39
Yieldb eec (%)
(%)
per million relative to tetramethylsilane. Splitting patterns are
designated as s, singlet; d, doublet; t, triplet; q, quartet; and m,
multiplet. 13C NMR spectra were recorded on a JEOL JNM EX270
(67.5 MHz), JEOL JNM ECS400 (100 MHz), JEOL JNM GSX500
(125 MHz), or JEOL JNM ECA600 (150 MHz) spectrometer with
complete proton decoupling. Chemical shifts are reported in parts
per million relative to tetramethylsilane with solvent resonance as
the internal standard CDCl3. High resolution mass spectra (HRMS)
were recorded on a JEOL JMS-SX-102A mass spectrometer (EI).
Elemental analyses were carried out on a Yanaco CHN Corder
MTe5. Analytical TLC was performed on Merck precoated TLC
plates (silica gel 60 GF254, 0.25 mm). Silica gel column chroma-
tography was carried out on silica gel 60 N (Kanto Kagaku Co., Ltd.,
1
2
3
4
5
6
7
30
60
81
74
78
85
51
0
98
99
92
95
97
d
30
spherical, neutral, 63e210 mm). Preparative thin-layer chromatog-
5
raphy (PTLC) was carried out on silica gel Wakogel Be5F. (2S,4S)-
Pentane-2,4-diol (2) was purchased from Wako Pure Chemical In-
dustries, Ltd. and used without purification (Lot No. ALQ4465, 97.0%
ee, [
a
]
20 þ52.9 (c 10, EtOH)). Characterization data of compounds 3,
D
120
180
4, 6, 8, 16, 29d, 30d, 34cef, 36, and 39aed were reported.4 Diols
15a,24, 15b,25, 15c,25, 15d,25 and 15e26 are known compounds. Acyl
silanes 35,27 38a,28 38b,29 38c,30 38d,30 38e, 38f, 38g,31 and 38h32
were prepared by the reported procedure.27 The absolute config-
uration was determined by converting alcohol to the corresponding
MTPA ester.33
10
90
0
d
4.1.1. (4R,5R)-4,5-Dimethyl-2-methyl-2-(2-phenylethyl)-1,3-dioxo-
lane (17). To a stirred mixture of 7 (50.2 mg, 0.34 mmol) and
(2R,3R)-butanediol 12 (34.2 mg, 0.38 mmol) in dry benzene (10 mL)
was added 2,4-dinitrobenzenesulfonic acid (4.9 mg, 0.017 mmol)
and the mixture was refluxed for 0.5 h with continuous azeotropic
removal of water. After cooling to room temperature, the reaction
was quenched with saturated aqueous NaHCO3 solution, and the
mixture was extracted with ethyl acetate. The combined organic
extracts were washed with brine, dried over anhydrous sodium
sulfate, filtered, and concentrated. The crude product was purified
by preparative TLC (hexane/ethyl acetate¼5:1) to afford 17
(41.7 mg, 0.19 mmol, 56%) as a colorless oil; 1H NMR (600 MHz,
8
17
74
a
For conditions, see Eq. 2.
Isolated yield.
Determined by chiral HPLC (see Experimental section).
b
c
under acidic conditions (entry 7). Asymmetric reduction of benzoyl
silane 38h proceeded very slowly, and the desired product 39h was
obtained in only 17% yield with 74% ee (entry 8).
CDCl3)
d
1.26 (d, J¼2.7 Hz, 3H), 1.27 (d, J¼3.4 Hz, 3H), 1.40 (s, 9H),
1.96 (m, 2H), 2.69e2.78 (m, 2H), 3.60e3.64 (m, 1H), 3.69e3.72 (m,
1H), 7.16e7.21 (m, 3H), 7.24e7.28 (m, 2H); 13C NMR (150 MHz,
3. Conclusion
CDCl3) d 16.4, 17.2, 25.9, 30.1, 42.2, 78.1, 79.0, 108.7, 125.6, 128.3,
142.2; IR (CHCl3, cmꢁ1) 1604, 1454; HRMS (EIþ) calcd for C14H20O2
Asymmetric reduction of aliphatic ketones proceeded by re-
action with chiral pentane-2,4-diol 2 in the presence of octanethiol
and a catalytic amount of DNBSA in benzene at reflux. On the other
hand, asymmetric reduction of various acyl silanes using DNBSA
(m/z) 220.14633, found 220.14580.
4.1.2. 2,8-Dimethylnon-5-en-4-one (19). Obtained as a colorless oil:
1H NMR (600 MHz, CDCl3)
d
0.92 (d, J¼4.8 Hz, 6H), 0.94 (d, J¼4.8 Hz,

J.-ichi Matsuo et al. / Tetrahedron 66 (2010) 6062e6069
6067
6H), 1.77 (sep, J¼6.9 Hz, 1H), 2.10 (t, J¼7.6 Hz, 2H), 2.15 (m, 1H), 2.40
(d, J¼6.9 Hz, 2H), 6.07, (d, J¼15.8 Hz, 1H), 6.79 (dt, J¼15.8, 7.6 Hz,
(m, 18H), 2.15 (br s, 0.33H), 2.48e2.55 (m, 2H), 2.62e2.67 (m,
0.55H), 2.78 (dtd, J¼4.1, 6.9, 9.6 Hz, 0.43H), 2.92 (br s, 0.46H), 3.70
1H); 13C NMR (150 MHz, CDCl3)
d
22.4, 22.7, 25.2, 27.9, 41.7, 49.1,
(m, 0.54H), 3.87 (m, 0.42H); 13C NMR (150 MHz, CDCl3)
d 9.8, 10.0,
131.8, 146.2, 200.6; IR (CHCl3, cmꢁ1) 1662, 1623, 1465; HRMS (EIþ)
11.0, 11.4, 14.1, 22.6; IR (CHCl3, cmꢁ1) 3417, 1463; HRMS (EIþ) calcd
calcd for C11H20O (m/z) 168.15142, found 168.15127.
for C15H32SO (m/z) 260.21739, found 260.21735.
4.1.3. 4-Octylsulfanylpentan-2-one (29d). Obtained as a colorless
4.1.10. 6-Octylsulfanylnonan-4-ol (32f). Obtained as a colorless oil:
oil: 1H NMR (600 MHz, CDCl3)
d
0.88 (t, J¼6.6 Hz, 3H), 1.24e1.32 (m,
1H NMR (600 MHz, CDCl3, a mixture of diastereomers, 55:45)
d 0.88
10H),1.35e1.38 (m, 3H) 1.57 (quin, J¼7.56, 2H), 2.16, (s, 3H), 2.52 (t,
J¼7.56, 2H), 2.57 (dd, J¼8.2, 17.2 Hz, 1H), 2.73 (dd, J¼6.2, 17.2 Hz,
(t, J¼6.9 Hz, 3H), 0.91-0.94, (m, 6H), 1.22e1.32 (m, 9H), 1.34e1.72
(m, 13H), 2.21 (br s, 0.37H), 2.46e2.55 (m, 2H), 2.68 (m, 0.54H), 2.84
(m, 0.45H), 2.95 (br s, 0.46H), 3.78 (m, 0.53H), 3.95 (m, 0.43H); 13C
1H), 3.23 (sex, J¼6.2 Hz, 1H); 13C NMR (150 MHz, CDCl3)
d 14.0, 21.5,
22.5, 28.8, 28.9, 29.0, 29.6, 30.5, 30.6, 31.7, 34.8, 50.9, 206.6; IR
(CHCl3, cmꢁ1) 1713, 1456; HRMS (EIþ) calcd for C13H26SO (m/z)
230.17044, found 230.17032.
NMR (150 MHz, CDCl3) d 14.00, 14.09, 18.66, 19.82, 20.11, 22.64,
29.04, 29.06, 29.16, 29.18, 29.20, 29.76, 29.78, 29.83, 30.10, 31.80,
37.97, 38.00, 40.04, 40.06, 41.24, 42.05, 42.29, 44.28, 69.04, 71.30; IR
(CHCl3, cmꢁ1) 3419, 1465; HRMS (EIþ) calcd for C17H36SO (m/z)
288.24869, found 288.24866.
4.1.4. 4-Octylsulfanylpentan-2-ol (30d). Obtained as a colorless oil:
1H NMR (600 MHz, CDCl3, a mixture of diastereomers, 57:43)
d 0.88
(t, J¼6.9 Hz, 3H), 1.20 (d, J¼6.2 Hz, 3H), 1.25e1.40 (m, 13H),
1.55e1.61 (m, 3H), 1.65e1.71 (m, 1H), 2.55 (t, J¼7.6 Hz, 2H), 2.87
(sex, J¼6.9 Hz, 0.44H), 2.98 (sex, J¼6.9 Hz, 0.59H), 3.96 (m, 0.44H),
4.2. General procedure for asymmetric reduction of ketones
(Table 7, entry 4)
4.11 (m, 0.58H); 13C NMR (150 MHz, CDCl3)
d
14.1, 22.1, 22.2, 23.7,
To a stirred mixture of 33c (49.4 mg, 0.44 mmol), (2S,4S)-pen-
23.9, 29.0, 29.1, 29.2, 29.7, 29.8, 29.9, 30.2, 31.8, 37.0, 38.1, 45.2, 45.7,
65.4, 67.0; IR (CHCl3, cmꢁ1) 3567, 1456; HRMS (EIþ) calcd for
C13H28SO (m/z) 232.18609, found 232.18592.
tane-2,4-diol
(2)
(49.8 mg,
0.48 mmol),
and
2,4-dini-
trobenzenesulfonic acid (DNBSA, 6.3 mg, 0.022 mmol) in dry
benzene (5 mL) was added a solution of 1-octanethiol (70.5 mg,
0.48 mmol) in dry benzene (5 mL), and the mixture was refluxed
for 1.5 h with continuous azeotropic removal of water. After cooling
to room temperature, the reaction was quenched with saturated
aqueous NaHCO3 solution, and the mixture was extracted with
ether. The combined organic extracts were washed with brine,
dried over anhydrous sodium sulfate, filtered, and concentrated.
The crude product was purified by column chromatography on
silica gel (hexane/Et2O¼40/1) to afford 34c4 (28.5 mg, 0.25 mmol
57%) as a colorless oil.
4.1.5. 5-Octylsulfanylheptan-3-one (31a). Obtained as a colorless
oil: 1H NMR (600 MHz, CDCl3)
d
0.88 (t, J¼7.6 Hz, 3H), 0.98 (t,
J¼7.6 Hz, 3H), 1.07 (t, J¼7.6 Hz, 3H), 1.24e1.38 (m, 10H), 1.53e1.62
(m, 4H), 2.41e2.50 (m, 4H), 2.59 (dd, J¼6.2, 16.5 Hz, 1H), 2.67 (dd,
J¼7.6, 16.5 Hz, 1H), 3.07 (quin, J¼6.2 Hz, 1H); 13C NMR (150 MHz,
CDCl3)
d 7.6, 11.2, 14.1, 22.6, 28.2, 29.0, 29.2, 29.8, 31.1, 31.8, 37.0,
42.4, 48.0, 209.8; IR (CHCl3, cmꢁ1) 1712, 1459; HRMS (EIþ) calcd for
C13H26SO (m/z) 230.17044, found 230.17032.
4.1.6. 2,6-Dimethyl-5-octylsulfanylheptan-3-one (31b). Obtained as
4.2.1. (R)-3,3-Dimethyl-4-phenyl-butan-2-ol
(34a)34. Compound
a colorless oil: 1H NMR (600 MHz, CDCl3)
d
0.88 (t, J¼6.9 Hz, 3H),
34a (>99% ee (R)) was obtained as a colorless oil. The enantiomeric
excess was determined by HPLC analysis using a chiral column.
Chiral HPLC: Daicel Chiralpak AD-H 46ꢂ150 mm, 254 nm UV de-
tector, room temperature, eluent: (hexane/i-PrOH) 40:1, flow rate:
0.92 (d, J¼6.2 Hz, 3H), 0.99 (d, J¼6.9 Hz, 3H), 1.10 (d, J¼2.1, 3H), 1.12
(d, J¼2.1 Hz, 3H), 1.24e1.38 (m, 10H), 1.53 (quin, J¼7.6 Hz, 2H), 1.88
(m, 1H), 2.50 (t, J¼7.6 Hz, 1H), 2.60e2.65 (m, 2H), 2.71 (dd, J¼8.9,
17.2 Hz, 1H), 3.07 (m, 1H); 13C NMR (150 MHz, CDCl3)
d
14.1, 17.9,
0.5 mL/min, retention time (min) 14.4 (R isomer). [
a
]
D
22 ꢁ7.93 (c 1.9,
18.0, 18.9, 19.6, 22.6, 28.9, 29.2, 29.8, 31.8, 32.4, 32.9, 41.6, 44.1, 47.8,
213.1; IR (CHCl3, cmꢁ1) 1713, 1456; HRMS (EIþ) calcd for C17H34SO
(m/z) 286.23304, found 286.23319.
CHCl3) (lit.34
[
a]
ꢁ4.66 (c 3.0, CHCl3)); 1H NMR (600 MHz, CDCl3)
D
d
0.80 (s, 3H), 0.86 (s, 3H),1.16 (d, J¼6.2 Hz, 3H), 2.50 (d, J¼13.1 Hz,
1H), 2.68 (d, J¼13.1 Hz, 1H), 3.53 (q, J¼6.2 Hz, 1H), 7.16e7.21 (m,
3H), 7.25e7.28 (m, 2H); 13C NMR (150 MHz, CDCl3)
d; 17.9, 21.7,
4.1.7. 2,8-Dimethyl-6-octylsulfanylnonan-4-one (31d). Obtained as
23.0, 38.6, 44.5, 73.7, 125.8, 127.7, 130.5, 138.9.
a colorless oil: 1H NMR (600 MHz, CDCl3)
d 0.86e0.92 (m, 15H),
1.24e1.42 (m, 12H), 1.53e1.57 (m, 2H), 1.81 (m, 1H), 2.15 (sep,
J¼6.9 Hz, 1H), 2.30 (dd, J¼2.7, 6.9 Hz, 2H), 2.48 (td, J¼6.9, 4.8 Hz,
2H), 2.55 (dd, J¼6.9, 17.2 Hz, 1H), 2.68 (dd, J¼6.9, 17.2 Hz, 1H), 3.14
4.2.2. (R)-2,2-Dimethylcyclopentanol (34b)35. Compound 34b (99%
ee (R)) was obtained as a colorless oil. The enantiomeric excess (93%
ee) was determined by HPLC analysis using a chiral column after
derivatization to the corresponding p-nitrobenzoate. Chiral HPLC:
Daicel Chiralpak ADeH 46ꢂ150 mm, 254 nm UV detector, room
temperature, eluent: (hexane/i-PrOH) 200:1, flow rate: 0.5 mL/min,
(m, 1H); 13C NMR (150 MHz, CDCl3)
d 14.1, 22.0, 22.6, 22.7, 22.9,
24.4, 25.5, 29.0, 29.2, 29.7, 30.6, 31.8, 38.5, 44.8, 50.0, 52.7, 209.1; IR
(CHCl3, cmꢁ1) 1708, 1467; HRMS (EIþ) calcd for C19H38SO (m/z)
314.26434, found 314.26412.
retention time (min) 13.3 (S isomer), 14.4 (R isomer). [
a
]
23 ꢁ19.49 (c
D
0.9, benzene) (lit.35
(600 MHz, CDCl3)
[
a]
ꢁ15.8 (c 10.1, benzene)); 1H NMR
D
4.1.8. 6-Octylsulfanylnonan-4-one (31f). Obtained as a colorless oil:
d
0.94 (s, 3H), 0.96 (s, 3H), 1.35e1.40 (m, 1H),
1H NMR (600 MHz, CDCl3)
d
0.88 (t, J¼6.9 Hz, 3H), 0.89e0.93 (m,
1.52e1.62 (m, 1H), 1.68e1.77 (m, 1H), 2.00e2.05 (m, 1H), 3.67 (t,
6H), 1.24e1.32 (m, 8H), 1.34e1.64 (m, 10H), 2.40 (td, J¼6.9, 4.8 Hz,
2H), 2.49 (td, J¼7.6, 2.1 Hz, 2H), 2.60 (dd, J¼6.9, 17.2 Hz, 1H), 2.67
(dd, J¼6.9, 17.2 Hz, 1H), 3.11 (quin, J¼6.9 Hz, 1H); 13C NMR
J¼5.5 Hz, 1H); 13C NMR (150 MHz, CDCl3)
d; 19.8, 21.2, 26.6, 32.6,
37.4, 42.0, 81.2.
(150 MHz, CDCl3)
d
13.7, 13.9, 14.1, 17.1, 20.0, 22.6, 29.0, 29.2, 29.8,
4.2.3. (R)-2-Methyl-5-phenyl-3-pentanol (34g)36. Compound 34g
(66% ee (R)) was obtained as a colorless oil. The enantiomeric excess
was determined by HPLC analysis using a chiral column Daicel
Chiralpak ADeH 46ꢂ150 mm, 254 nm UV detector, room temper-
ature, eluent: (hexane/i-PrOH) 20:1, flow rate: 0.5 mL/min, re-
31.0, 31.8, 37.6, 40.4, 45.7, 48.9, 209.4; IR (CHCl3, cmꢁ1) 1710, 1465;
HRMS (EIþ) calcd for C17H34SO (m/z) 286.23304, found 286.23317.
4.1.9. 5-Octylsulfanylheptan-3-ol (32a). Obtained as a colorless oil:
1H NMR (600 MHz, CDCl3, a mixture of diastereomers, 56:44)
d
0.88
tention time (min) 10.2 (S isomer), 10.9 (R isomer). [
a
]
30 þ25.19 (c
D
(t, J¼6.9 Hz, 3H), 0.94e0.97 (m, 3H), 0.98e1.02 (m, 3H), 1.22e1.72
3.0, EtOH); 1H NMR (500 MHz, CDCl3)
d
0.90 (d, J¼6.8 Hz, 6H), 1.61

6068
J.-ichi Matsuo et al. / Tetrahedron 66 (2010) 6062e6069
(br s, 1H), 1.67 (m, 1H), 2.63 (m, 1H), 2.83 (ddd, J¼5.2 10.0, 13.7 Hz,
1H), 3.37 (ddd, J¼3.6, 5.2, 8.8 Hz, 1H), 7.15e7.21 (m, 3H), 7.25e7.28
and the mixture was heated at reflux for 0.5 h with continuous
azeotropic removal of water. After cooling to room temperature, the
reactionwas quenched with saturated aqueous NaHCO3 solution, and
the mixture was extracted with ethyl acetate. The combined organic
extracts were washed with brine, dried over anhydrous sodium sul-
fate, filtered, and concentrated. The crude product was purified by
column chromatography on silica gel (hexane/ethyl acetate¼20/1) to
afford 364 (64.3 mg, 0.31 mmol 83%) as a colorless oil.
(m, 2H); 13C NMR (125 MHz, CDCl3)
125.7, 128.3, 128.4, 142.3.
d 17.1, 18.7, 32.4,33.6, 35.9, 76.0,
4.2.4. (R)-Heptan-2-ol (34h)37. Compound 34h (51% ee (R)) was
obtained as a colorless oil. The enantiomeric excess was de-
termined by HPLC analysis using a chiral column after de-
rivatization to the corresponding benzoate. Chiral HPLC: Daicel
Chiralpak AD-H 46ꢂ150 mm, 254 nm UV detector, room tempera-
ture, eluent: (hexane/i-PrOH) 200:1, flow rate: 0.5 mL/min, re-
4.3.1. (S)-1-tert-Butyldimethylsilyl-3-methybutan-1-ol (39e). Com-
pound 39e (97% ee (S)) was obtained as a colorless oil. The enantio-
meric excess was determined by HPLC analysis using a chiral column
after derivatization to the corresponding p-nitrobenzoate. Chiral
HPLC:DaicelChiralpak OD-H46ꢂ150 mm, 254 nmUVdetector, room
temperature, eluent: (hexane/i-PrOH) 400:1, flow rate: 0.5 mL/min,
tention time (min) 6.6 (R isomer), 7.3 (S isomer). [
a
]
29 ꢁ5.54 (c 0.67,
D
CHCl3); 1H NMR (400 MHz, CDCl3)
d
; 0.89 (t, J¼6.9 Hz, 3H), 1.17 (d,
J¼6.0 Hz, 3H), 1.26e1.48 (m, 9H), 3.77 (m, 1H); 13C NMR (100 MHz,
CDCl3)
d 14.0, 22.6, 23.3, 25.4, 31.8, 39.2, 68.0.
retention time (min): 7.4 (R isomer), 10.7 (S isomer). [
a
]
20 þ19.46 (c
D
4.2.5. (R)-Octan-2-ol (34i)35. Compound 34i (52% ee (R)) was
obtained as a colorless oil. The enantiomeric excess was determined
by HPLC analysis using a chiral column after derivatization to the
corresponding benzoate. Chiral HPLC: Daicel Chiralpak ADeH
46ꢂ150 mm, 254 nm UV detector, room temperature, eluent:
(hexane/i-PrOH) 300:1, flow rate: 0.5 mL/min, retention time (min):
0.8, CHCl3); 1H NMR (400 MHz, CDCl3)
d
ꢁ0.06 (s, 3H), 0.01 (s, 3H),
0.90(d, J¼6.9 Hz,3H), 0.94(m,12H),1.17(ddd, J¼2.3,10.5,14.2 Hz,1H),
1.58 (ddd, J¼2.3,12.4,14.2 Hz, 1H),1.80e1.90 (m, 1H), 3.59 (dd, J¼2.3,
12.4 Hz, 1H); 13C NMR (100 MHz, CDCl3)
d
ꢁ8.7, ꢁ7.7, 16.8, 20.8, 24.0,
24.1, 27.1, 43.4, 61.9; IR (CHCl3, cmꢁ1) 1250, 1466, 3603.
6.6 (Risomer), 7.2 (Sisomer). [
a
]
20 ꢁ4.19 (c1.0, CHCl3) (lit.35
[
a
]D ꢁ5.8
4.3.2. (S)-a
-(Trimethylsilyl) benzyl alcohol (39h)24. Compound 39h
D
(c 8.8, CHCl3)); 1H NMR (400 MHz, CDCl3)
d
0.89 (m, 3H), 1.17 (d,
(74% ee (S)) was obtained as a colorless oil. The enantiomeric excess
was determined by HPLC analysis using a chiral column Daicel Chir-
alpak OD-H 46ꢂ150 mm, 254 nm UV detector, room temperature,
J¼5.5 Hz, 3H), 1.22e1.50 (m, 10H), 1.95 (br s, 1H), 3.77 (m, 1H); 13C
NMR (100 MHz, CDCl3) d 14.0, 22.5, 23.3, 25.7, 29.3, 31.8, 39.3, 68.0.
eluent: (hexane/i-PrOH) 20:1, flow rate: 0.5 mL/min, retention time
30
4.2.6. (R)-Nonane-2-ol (34j)38. Compound 34j (51% ee (R)) was
obtained as a colorless oil. The enantiomeric excess was de-
termined by HPLC analysis using a chiral column after de-
rivatization to the corresponding benzoate. Chiral HPLC: Daicel
Chiralpak ADeH 46ꢂ150 mm, 254 nm UV detector, room temper-
ature, eluent: (hexane/i-PrOH) 300:1, flow rate: 0.5 mL/min, re-
(min): 8.85 (S isomer), 12.2 (R isomer). [
a
]
ꢁ59.37 (c 0.16,CHCl3)
D
(lit.20c
[a
]D ꢁ79.7 (c 1.08, CHCl3)); 1H NMR (600 MHz, CDCl3)
d 0.02 (s,
9H),1.68 (br s,1H), 4.53 (s,1H), 7.16e7.20 (m, 3H), 7.30e7.32 (m, 2H);
13C NMR (150 MHz, CDCl3)
d
ꢁ4.2, 70.6, 124.9, 125.8, 128.1, 144.2.
23 ꢁ6.35 (c
Acknowledgements
tention time (min): 6.40 (R isomer), 6.87 (S isomer). [
a
]
D
0.88, CHCl3) (lit.38
[
a]
ꢁ6.95 (c 1.1, CHCl3)); 1H NMR (600 MHz,
D
This work was partially supported by a Grant-in-Aid for Scien-
tific Research from the Ministry of Education, Culture, Sports, Sci-
ence, and Technology, Japan. The authors thank Teijin Pharma Ltd.
for financial support and also thank Dr. Osamu Nishikawa, Mr.
Kenzo Watanabe, Mr. Jun-ichi Oshida, and Mr. Toru Minoshima (all
in Teijin Pharma Ltd.) for discussions.
CDCl3)
d
0.88 (t, J¼6.5 Hz, 3H), 1.18 (d, J¼6.2 Hz, 3H), 1.25e1.58 (m,
13H), 3.79 (sex, J¼1H); 13C NMR (150 MHz, CDCl3)
d 14.1, 22.6, 23.4,
25.7, 29.3, 29.6, 31.8, 39.3, 68.2.
4.2.7. (Z)-1-Octylsulfanyl-3-phenyl-1-trimethylsilylprop-1-en (37).
To a stirred mixture of 35 (49.4 mg, 0.24 mmol), (2S,4S)-pentane-
2,4-diol 2 (28.5 mg, 0.27 mmol) and 2,4-dinitrobenzenesulfonic
acid (DNBSA, 3.4 mg, 0.012 mmol) in dry benzene (5 mL) was added
a solution of 1-octanethiol (70.5 mg, 0.48 mmol) in dry benzene
(5 mL), and the mixture was refluxed for 20 min with continuous
azeotropic removal of water. After cooling to room temperature, the
reaction was quenched with saturated aqueous NaHCO3 solution,
and the mixture was extracted with ethyl acetate. The combined
organic extracts were washed with brine, dried over anhydrous
sodium sulfate, filtered, and concentrated. The crude product was
purified by preparative TLC (hexane/benzene¼20:1) to afford 37
(20.2 mg, 0.060 mmol, 25%) as a colorless oil; 1H NMR (600 MHz,
References and notes
1. (a) Wilds, A. L. Org. React. 1944, 2, 178; (b) de Graauw, C. F.; Peters, J. A.; van
Bekkum, H.; Huskens, J. Synthesis 1994, 1007.
2. (a) Kow, R.; Nygren, R.; Rathke, M. W. J. Org. Chem. 1977, 42, 826; (b) Akamanchi,
K. G.; Varalakshmy, N. R. Tetrahedron Lett. 1995, 36, 3571; (c) Ooi, T.; Miura, T.;
Maruoka, K. Angew. Chem., Int. Ed. 1998, 37, 2347; (d) Campbell, E. J.; Zhou, H.;
Nguyen, S. T. Org. Lett. 2001, 3, 2391; (e) Ooi, T.; Itagaki, Y.; Miura, T.; Maruoka,
K. Tetrahedron Lett. 1999, 40, 2137; (f) Gal, G.; Krasznai, I. Magy. Kem. Foly. 1956,
62, 155; (g) Gal, G.; Krasznai, E. Acta Chim. Acad. Sci. Hung. 1958, 17, 171; (h) Ko,
B.-T.; Wu, C.-C.; Lin, C.-C. Organometallics 2000, 19, 1864; (i) Konishi, K.; Makita,
K.; Aida, T.; Inoue, S. J. Chem. Soc., Chem. Commun. 1988, 643; (j) Namy, J. L.;
Souppe, J.; Collin, J.; Kagan, H. B. J. Org. Chem. 1984, 49, 2045; (k) Lebrun, A.;
Namy, J. L.; Kagan, H. B. Tetrahedron Lett. 1991, 32, 2355.
CDCl3)
d
0.17 (s, 9H), 0.88 (t, J¼6.9 Hz, 3H), 1.22e1.40 (m, 10H), 1.57
(quin, J¼7.6 Hz, 2H), 2.65 (t, J¼7.6 Hz, 2H), 3.78 (d, J¼6.2 Hz, 2H),
3. Asymmetric catalysis (a) Evans, D. A.; Nelson, S. G.; Gagne, M. R.; Muci, A. R.
J. Am. Chem. Soc. 1993, 115, 9800; (b) Campbell, E. J.; Zhou, H.; Nguyen
SonBinh, T. Angew. Chem., Int. Ed. 2002, 41, 1020.
6.37 (t, J¼6.9 Hz, 1H); 13C NMR (150 MHz, CDCl3)
d
ꢁ0.7, 14.1, 22.6,
28.8, 29.1, 29.2, 30.1, 31.8, 34.6, 36.9, 125.9,128.4, 136.9, 140.3, 146.2;
IR (CHCl3, cmꢁ1) 1602, 1247; HRMS (EIþ) calcd for C13H26SO (m/z)
230.17044, found 230.17032. The (Z)-configuration was determined
by NOE experiments (between CH]C and Me3Si).
4. Matsuo, J.; Hattori, Y.; Ishibashi, H. Org. Lett. 2010, 12, 2294.
5. Matsuo, J.; Kozai, T.; Nishikawa, O.; Hattori, Y.; Ishibashi, H. J. Org. Chem. 2008, 73, 6902.
6. (a) Mori, A.; Fujiwara, J.; Maruoka, K.; Yamamoto, H. Tetrahedron Lett.1983, 24, 4581;
(b) Mori, A.; Fujiwara, J.; Maruoka, K.; Yamamoto, H. J. Organomet. Chem.1985,285, 83.
7. Dauben, W. G.; Gerdes, J. M.; Look, G. C. J. Org. Chem. 1986, 51, 4964.
8. (a) Corey, E. J.; Helal, C. J. Angew. Chem., Int. Ed. 1998, 37, 1986; (b) Itsuno, S. Org.
React. 1998, 52, 395.
9. Dong, H.; Du, H.; Wickramasinghe, S. R.; Qian, X. J. Phys. Chem. B 2009,113,14094.
10. Crumrine, D. S.; Shankweiler, J. M.; Hoffman, R. V. J. Org. Chem. 1986, 51, 5013.
11. Bos, M.; Dahmen, E. A. M. F. Anal. Chim. Acta 1971, 57, 361.
4.3. General procedure for asymmetric reduction of acyl
silanes (Eq. 2)
To a stirred mixture of 35 (77.0 mg, 0.37 mmol) and (2S,4S)-pen-
tane-2,4-diol 2 (42.2 mg, 0.40 mmol) in dry benzene (10 mL) was
added 2,4-dinitrobenzenesulfonic acid (DNBSA, 5.3 mg, 0.019 mmol),
12. Acetal 24 was not detected in DNBSA-catalyzed reduction of ketones with anti-
1,3-diols 15. On the other hand, syn-1,3-diol 11 gave the corresponding acetal
16 which has two methyl groups both in equatorial positions (Table 4, entry 4).

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