K. Fukuda et al. / Tetrahedron Letters 51 (2010) 4523–4525
4525
DIBAL followed by the hydrogenation of the resulting alkynyl alco-
hol over Lindlar’s catalyst in 98% overall yield.
1) mCPBA, CH2Cl2
(ClCH2CO)2O
pyridine
Me
(99%)
OH
SiPhMe2
rac-12
The stereochemistry of the allylsilanes was determined as
shown in Scheme 6. The hydrogenetion of allylsilane (S)-11 fol-
lowed by acetylation afforded acetate (S)-15 which was subjected
to the Tamao oxidation reaction. The optical rotation value of the
product (S)-16 was compared with that of the known hydroxy es-
SiPhMe2
Me
CH2Cl2
96%
2) Me
MgBr
CuBr·SMe2
BF3·OEt2, THF (89%)
16
O
ter, showing that the configuration of the allylsilane as S.
Lipase QLM
Cl
In summary, we have developed practical methods for the syn-
thesis of the optically active 2-(dimethylphenylsilyl)-3-penten-1-
ols with high enantiopurity. That is, the optically pure (E)-allylsi-
lane (R)-10 was synthesized from commercially available (R)-3-bu-
tyn-2-ol in five steps involving the alkylation reaction of the
alkenylzirconocene intermediate with BOMCl as the key step. On
the other hand, both enantiomers of (Z)-allylsilanes, (R)-11 (97%
ee) and (S)-11 (96% ee), were successfully prepared from commer-
cially available dimethylphenylvinylsilane through epoxidation,
the regioselective epoxide-opening reaction with 1-propynylmag-
nesium bromide, and subsequent optical resolution using the li-
pase QLM. The synthetic potential and utility of these optically
active allylsilanes will be described in the following Letter.
(R)-12
(S)-13
O
phosphate buffer
acetone, 3 ºC
55%
38%
SiPhMe2
rac-13
(66%ee)
(96%ee)
(ClCH2CO)2O
pyridine
Lipase QLM
(R)-12
(R)-13
(R)-12
phosphate buffer
acetone, 3 ºC
CH2Cl2, rt
98%
(66%ee)
(66%ee)
(97%ee)
43%
Lindlar's cat.
H2, AcOEt
99%
1) DIBAL
Acknowledgments
THF (100%)
OH
OH
Me SiPhMe2
(R)-11
(S)-13
Me SiPhMe2
2) Lindlar's cat.
H2, AcOEt
98% (Z/E=98:2)
This work was partially supported by the Global COE Program
(Project No. B01: Catalysis as the Basis for Innovation in Materials
Science) and Grant-in-Aid for Scientific Research on Innovative
Areas (Project No. 2105: Organic Synthesis Based on Reaction Inte-
gration) from the Ministry of Education, Culture, Sports, Science,
and Technology, Japan.
(96%ee)
(S)-11
Scheme 5. Synthesis of the optically active allylsilane 11.
Next, we turned our attention to the development of practical
methods for the synthesis of the optically active (Z)-allylsilanes,
(R)-11 and (S)-11. Since the palladium-catalyzed intramolecular si-
lyl transfer reaction is not applicable to a (Z)-alkene, we set out to
use optical resolution of racemic alcohols by enzyme.14 To this
end, initially, commercially available dimethylphenylvinylsilane
was oxidized to the corresponding epoxy silane, which was sub-
jected to the ring-opening reaction with 1-propynylmagnesium bro-
mide in the presence of CuBrÁSMe2 and BF3ÁOEt2 to furnish rac-12 in
high overall yield (Scheme 5). The alcohol 12 was then converted to
chloroacetate 13 and the subsequent key asymmetric hydrolysis of
theacetatewascarriedoutinaphosphatebuffersolutioninthepres-
ence of a lipase.15 After a number of trials, lipase QLM was found to
afford the alcohol (R)-12 with 66% ee in 55% yield, along with 38%
of the ester (S)-13 with 96% ee. The optical purity of the products
was evaluated by a HPLC analysis using a chiral column.
Supplementary data
Supplementary data (experimental procedures and character-
ization data for the allylsilanes) associated with this article can
References and notes
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H
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Ac2O
pyridine
DMAP
H2, PtO2
OH
OH
Me SiPhMe2
(S)-11
SiPhMe2
(S)-14
CH2Cl2
93%
AcOEt
95%
AcOOH
KBr
OAc
SiPhMe2
(S)-15
NaOAc
OAc
OH
AcOH
76%
(S)-16
15. The reactions of the corresponding acetate with lipases in a buffer solution
were found to be extremely sluggish.
16. Ishihara, K.; Sakai, T.; Tsuboi, S.; Utaka, M. Tetrahedron Lett. 1994, 35, 4569.
Scheme 6. Determination of the stereochemistry of the allylsilane.