An elimination approach to the synthesis of (+)-Scorodonin

Article abstract of DOI:10.1002/cjoc.201090277

1,2-Elimination of optically-active vinyl sulfoxide-allylic acetates led to corresponding allenynes in excellent yields. When the chirality of the sulfinyl group "matched" that at the allylic position, the chirality at the allylic stereogenic center could be efficiently transferred to the allenic axis.

Full text of DOI:10.1002/cjoc.201090277

FULL PAPER
An Elimination Approach to the Synthesis of (＋)-Scorodonin†
Zhang, Yan(张艳)
Wu, Yikang*(伍贻康)
State Key Laboratory of Bioorganic and Natural Products Chemistry, Shanghai Institute of Organic Chemistry,
Chinese Academy of Sciences, 345 Lingling Road, Shanghai 200032, China
1,2-Elimination of optically-active vinyl sulfoxide-allylic acetates led to corresponding allenynes in excellent
yields. When the chirality of the sulfinyl group “matched” that at the allylic position, the chirality at the allylic
stereogenic center could be efficiently transferred to the allenic axis.
Keywords elimination, natural products, allenes, alkynes, sulfoxides
Introduction
Results and discussion
Scorodonin (1) is a natural antibiotic isolated from
Marasmius scorodonius.1 Preliminary biotesting has
shown that this compound can inhibit the growth of
bacteria, yeasts and filamentous fungi, and the incorpo-
ration of thymidine and uridine into DNA and RNA in
cells of the ascitic form of Ehrlich carcinoma. Recently,
we reported the first synthesis of this natural product,
with the key allenic axis formed in 63% ee via a cou-
pling reaction between an optically-active bromoallene
(95% ee) and a zincated terminal alkyne.2 Because the
chirality transfer in this case was not as good as that in
the similar couplings in our synthesis of Nemotin3 (2)
and Phomallenic acid C4 (3) (Figure 1), alternative ap-
proaches were also sought. Herein we wish to report an
elimination approach to the construction of an allenyne
intermediate, from which using our earlier procedures it
would be possible to obtain the antipode of the natural
Scorodonin.
1,2-Elimination of optically-active sulfoxide-allylic
acetates leading to corresponding allenes was initially
developed by Satoh and co-workers.5 Although this ap-
proach is not so atom-economic as elimination of simi-
lar iodides,6 it does enjoy a distinct advantage—the di-
astereomers of the elimination precursors (sulfoxide-
allyl alcohols, vide infra) are often separable by chro-
matography on silica gel because of the sulfoxide
chirality. This benefit is particularly evident when both
epimers of the allylic stereogenic center are needed in
the studies, such as the present one.
The optically-active sulfinyl functionality required
for chromatographic separation of the two allylic
epimers and consequent definition of the absolute
stereochemistry of the allenic axis at a later stage of the
synthesis was prepared according to the literature pro-
cedures. In the event, treatment of thioanisole (4) with
NCS (N-chloro-succinimide) in CCl4 at ambient tem-
perature followed by heating with P(OEt)3 gave the de-
sired phenylthiomethylphosphate 5 in 79% overall yield
(Scheme 1).7 Asymmetric oxidation of the 5 was real-
ized under the conditions of (i-PrO)4Ti/(R)-BINOL
(1,1'-bi-2-naphthol)/TBHP (tert-butylhydroperoxide) as
reported by Naso and coworkers.8
7
O
Cl
O
H
3
C
2
4
H
C
(aS)
1
1
H
H
OH
Scorodonin
Condensation of the resulting optically-active sulf-
oxide 6 (88.5% ee) with the known aldehyde 79 in the
presence of LiCl/DBU/MeCN delivered the α,β-unsatu-
rated sulfoxide 810 in 60% yield as a 4∶1 mixture of
the (E)/(Z) isomers. As in the next step of reaction both
isomers reacted in the same way leading to a single
double bond isomer, it was not necessary to isolate the
two C-C double bond isomers at this stage.
2
Nemotin
OH
O
H
3
C
Phomallenic acid C
H
The mixture of the (E)/(Z) isomers was deprotonated
with LDA (lithium diisopropylamide) in THF at －78
Figure 1 The structures of natural Scorodonin (1), Nemotin (2),
and Phomallenic acid C (3).
*
E-mail: yikangwu@sioc.ac.cn
Received May 4, 2010; revised and accepted July 16, 2010.
Project supported by the National Basic Research Program of China (973 Program) (No. 2010CB833200), the National Natural Science Foundation
of China (Nos. 20921091, 20672129, 20621062, 20772143) and the Chinese Academy of Sciences (“Knowledge Innovation”, KJCX2.YW.H08).
† Dedicated to the 60th Anniversary of Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences.
Chin. J. Chem. 2010, 28, 1635— 1639
© 2010 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
1635

Zhang & Wu
FULL PAPER
Scheme 1
Scheme 2
1) NCS/CCl4
r.t./1 h
2) P(OEt)3
(R)
(S)
(i-PrO)4Ti
(R)-BINOL
TBHP
(S)
O
O
S
OH
O
S
OH
O
P
SMe
OEt
OEt
O
Ph
.
Ph
.
P OEt
OEt
Ph
.
S
.
.
120 oC
CCl4/r.t.
60 h, 44%
(S)
(S)
SPh
.
TESO
TESO
79% from 2
6
10a
TBSO
10b TBSO
5
4
(The more polar isomer)
(The less polar isomer)
LiCl/DBU
MeCN/rt
60%
Ac2O/CH2Cl2
91%
Ac2O/CH2Cl2
DMAP/Py
(R)
TBSO
CHO
90%
O
S
OH
DMAP/Py
7
Ph
(less polar)
(R)
(S)
.
.
O
S
OAc
O
S
OAc
(S)
Ph
Ph
(R)
TESO
TESO
.
.
TBSO
O
10a
.
.
CHO
9
(S)
(S)
Ph
S
(10a/10b 1:1.28)
(S)
TESO
100%
TESO
80%
.
11a
TBSO
11b TBSO
.
LDA/THF/−78 oC
74%
O
S
OH
8
TBSO
(E)/(Z) 4:1
Ph
.
(S)
i-PrMgBr/THF
−100 oC/15 min
i-PrMgBr/THF
−100 oC/15 min
.
(more polar)
TESO
10b TBSO
OTES
48% ee
87% ee
OTES
TBSO
(aS)
C
℃ to generate the corresponding carbanion, which on
reaction with aldehyde 9 [could be readily prepared
from TES (triethylsilyl) protected proparyl alcohol and
DMF (N-dimethylformamide)] afforded a pair of sepa-
rable epimers (10a and 10b) in a 1∶1.28 ratio. The
configurations of the newly formed allylic stereogenic
centers in 10a and 10b were not experimentally deter-
mined at this stage, but deduced later from the end
products with the aid of the rules embedded in Satoh’s
work.5
H
(aR)
C
H
12b
H
H
12a
[α]D24 +98.2
OTBS
ref. 2
(+)-Scorodonin
genic center appeared also to have a substantial influ-
ence. With 11b as the substrate, which led to the (aS)
allene in the end, the efficiency for the chirality transfer
from the allylic position to the allenic axis was excellent
at a wide range of temperatures (Table 1, Entries 1—5).
In the beginning we expected similar efficiency with the
other isomer (11a) because at a glance the configuration
of the sulfinyl group did not seem to have any direct
relation to the elimination. Interestingly, the efficiency
for the chirality transfer in the case of 11a, which was of
(R) configuration at the allylic position, turned out to be
much lower than observed with 11b (Table 1, Entry 6).
Satoh et al.5 had also mentioned similar cases in their
work, though without any explanation or comments. It
seems that there exists a delicate interaction between the
configurations of the sulfinyl group and the allylic
stereogenic center. When the configuration at these two
positions matches with each other, the chirality at the
allylic carbon can be transferred to the allenic axis in a
highly stereoselective manner.
The hydroxyl groups in 10a and 10b were then con-
verted into better leaving groups, respectively, by ace-
tylation with Ac2O in the presence of pyridine and
DMAP (4-dimethylaminopyridine) (Scheme 2). The
resulting 11a and 11b were then converted, respectively,
into corresponding allenes using the conditions of
Satoh.5 Thus, treatment of the acetates 11a or 11b with
i-PrMgBr in THF led to clean formation of the corre-
sponding allene. The reaction proceeded very fast even
at －100 ℃ (Table 1), requiring less than 15 min to go
to completion.
It is well established that the chiralty of the newly
formed allenic axis is dictated by the allylic stereogenic
center. However, the relative configuration of the
sulfinyl group with respect to that of the allylic stereo-
It should be noted that because 12a (the antipode of
12b) was an advanced intermediate in our previous
synthesis of (－)-Scorodonin, from 12b following the
procedure in that work would lead to (＋)-Scorodonin
of the same enantiopurity (87% ee), the antipode of 1. If
using the (R) sulfoxide instead of the (S) one (6) as used
in this work in the beginning, the same route should
allow for synthesis of natural Scorodonin.
Table 1 Reaction of 11 with i-PrMgBr in THF leading to 12
Entry Substrate Temperature
Product (yield, ee)
Eff.a
1
2
3
4
5
6
11b
11b
11b
11b
11b
11a
－30 ℃
－45 ℃
－60 ℃
－78 ℃
－100 ℃
－100 ℃
12b (93%, 85% ee) 96%
12b (93%, 84% ee) 94%
12b (93%, 82% ee) 93%
12b (90%, 84% ee) 95%
12b (80%, 87% ee) 98%
12a (100%, 48% ee) 54%
Conclusion
a Efficiency for the chirality transfer, defined as ee value of the
An elimination approach to the synthesis of the
product 12/the ee value of the starting 11 employed.
1636
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Chin. J. Chem. 2010, 28, 1635— 1639

An Elimination Approach to the Synthesis of (＋)-Scorodonin
chiral allene-alkyne assembly of the natural antibiotic
Scorodonin was developed. Starting from the (S)-sulf-
oxide of 88.5% ee, (aS)-allenyne was obtained in 87%
ee. The stereoselectivity is substantially higher than that
(63% ee) of the bromoallene-alkyne coupling approach
adopted in our previous synthesis. Following the pro-
cedures of deprotection and chlorination of 12a de-
scribed in that work, it should be possible to obtain
(＋)-Scorodonin from 12b. Similarly, using a (R)-sulf-
oxide instead of the (S) one may eventually give the
natural Scorodonin in significantly improved enantiose-
lectivity.
onto a silica gel column, first eluting with Et2O to re-
cover the unreacted starting phenylthiomethylphosphate
(1.196 g, 46%), then with EtOAc/MeOH (V∶V＝10∶1)
to obtain the known 6 (1.214 g, 44%) as a yellowish
liquid. [α] 2D3 ＋98.6 (c 1.0, CHCl3) [Lit.8 [α]D ＋98.1 (c
1.0, CHCl3)], 88.5% ee [tR(major)＝11.40 min, tR(minor)
＝13.06 min] as determined by HPLC on a CHIRAL-
PAK OJ-H column (0.46 cm×25.0 cm) eluting with
n-hexane/i-PrOH (V∶V＝80∶20) at a flow rate of 0.7
1
mL/min with the UV detector set to 214 nm. H NMR
(CDCl3, 500 MHz) δ: 7.73—7.70 (m, 2H), 7.53—7.50
(m, 3H), 4.18—4.05 (m, 4H), 3.39 (t, J＝14.6 Hz, 1H),
3.27 (dd, J＝15.4, 14.6 Hz, 1H), 1.30 (dt, J＝0.5, 7.1
Hz, 3H), 1.27 (dt, J＝0.5, 7.1 Hz, 3H).
Experimental
(R,E)-3-tert-Butyldimethylsilyloxy-prop-1-enyl-
phenylsulfoxide (8) A solution of 6 (1.26 g, 4.56
mmol), DBU (0.744 mL, 4.98 mmol), LiCl (228 mg,
5.38 mmol) and aldehyde 7 (722 mg, 4.15 mmol) in dry
MeCN (25 mL) was stirred at ambient temperature
overnight. Removal of the volatiles on a rotary evapo-
rator left a residue, which was chromatographed
[V(PE)∶V(Et2O)∶V(CH2Cl2)＝9∶2∶1] on silica gel
to give pure (E)-isomer (accounted for the majority of
the product) along with a mixture of the (E)/(Z) isomers
(737 mg altogether, 2.49 mmol, 60%) as colorless oils.
Data for the (E)-isomer (the less polar component):
Dry THF was distilled over Na/Ph2CO under N2
prior to use. Dry CH2Cl2, dry DMF, and dry MeCN
were distilled over CaH2 under N2 prior to use. Addition
of air/moisture sensitive reagents was done using sy-
ringe techniques. PE (for chromatography) stands for
petroleum ether (b.p. 60—90 ℃). Column chromato-
graphy was performed on silica gel (300—400 mesh)
under slightly positive pressure. NMR spectra were re-
corded on a Varian Mercury or a Bruker Avance NMR
1
spectrometer operating at 300, 400, or 500 MHz for H
as indicated for each individual compound below with
Me4Si as the internal standard. IR spectra were meas-
ured on a FT-IR 440 or a Nicolet Avatar 360 infrared
spectrometer. ESI-MS data were acquired on a
HP5989A mass spectrometer. HRMS data were ob-
tained with a Bruker APEXIII 7.0 Tesla FT-MS spec-
trometer. Optical rotations were measured on Perkin-
Elmer Polarimeter 341 or an Agilent Technologies
P-1030 Polarimeter.
Diethyl (S)-phenylsulfinylmethylphosphate (6)
NCS (3.725 g, 27.9 mmol) was added to a solution of 4
(3.0 mL, 25.4 mmol) in CCl4 (25 mL) stirred at ambient
temperature. Stirring was continued for 11 h. The white
solids were filtered off. The filtrate was concentrated on
a rotary evaporator. To the residue was added triethyl
phosphite (5.3 mL, 30.48 mmol). The mixture was
stirred in a 120 ℃ oil bath for 48 h. After being cooled
to ambient temperature, the mixture was chromato-
graphed [V(EtOAc)∶V(PE)＝1∶1] on silica gel to
give the intermediate diethyl phenylthiomethylphosph-
ate (5.2 g, 79% from 4) as a yellowish oil.
A solution of (i-PrO)4Ti (80 µL, 0.27 mmol) in CCl4
(6.0 mL) was added to a solution of (R)-BINOL ([α] D25
＋33.4 (c 1.0, THF), 145 mg, 0.51 mmol) in CCl4 (40
mL) stirred at ambient temperature. To the resulting
solution was added H2O (91 µL, 5.0 mmol). Stirring
was continued at ambient temperature for 1 h before a
solution of the above mentioned diethyl phenylthio-
methylphosphate (2.6 g, 10 mmol) in CCl4 (6.0 mL) was
introduced. The mixture was stirred for another 30 min.
tert-Butylhydroperoxide (＞65% aq. solution, 1.72 mL,
12.2 mmol) was added. Stirring was then continued at
ambient temperature for 3 d. The mixture was loaded
1
[α] 2D4 ＋118.0 (c 1.0, CHCl3); H NMR (CDCl3, 400
MHz) δ: 7.65—7.60 (m, 2H), 7.53—7.42 (m, 3H), 6.67
(dtd, J＝14.9, 3.4, 0.3 Hz, 1H), 6.49 (dt, J＝14.9, 1.9
Hz, 1H), 4.37 (dd, J＝3.6 2.2 Hz, 2H), 0.86 (s, 9H),
0.03 (s, 3H), 0.02 (s, 3H); 13C NMR (CDCl3, 100 MHz)
δ: 143.8, 138.1, 133.4, 130.9, 129.2, 124.4, 62.0, 25.7,
25.6, 18.2, －5.6; FT-IR (film) ν: 3311, 2926, 2881,
1616, 1442, 1089, 1028, 932, 757, 692 cm–1; ESI-MS
m/z: 297.0 ([M＋H]＋); ESI-HRMS calcd for C15H25Si-
O2S 297.1339 ([M＋H]＋), found 297.1341.
(3R)-7-tert-Butyldimethylsilyloxy-5-((S)-phenyl-
sulfinyl)-1-triethylsilyloxy-hept-5-en-2-yn-3-ol (10a)
and (3S)-7-tert-butyldimethylsilyloxy-5-((S)-phenyl-
sulfinyl)-1-triethylsilyloxy-hept-5-en-2-yn-3-ol (10b)
－1
n-BuLi (2.5 mol•L , in hexanes, 8.8 mL, 22 mmol)
was added dropwise to a solution of Et3SiOCH2C≡CH
(3.4 mL, 20 mmol) in dry THF (40 mL) stirred at 0 ℃.
Stirring was continued at the same temperature for 15
min. Then the bath temperature was cooled to －78 ℃
before dry Me2NCHO (2.32 mL, 30 mmol) was intro-
duced dropwise. The stirring was continued while bath
was allowed to warm slowly to ambient temperature.
Aq. sat. NH4Cl was added. The mixture was extracted
with Et2O, washed with water and brine, and dried over
anhydrous Na2SO4. Removal of the solvent on a rotary
evaporator and column chromatography [V(EtOAc)∶
V(PE)＝1∶100] on silica gel gave the aldehyde 9 (3.8 g,
1
19 mmol, 95%) as a colorless oil. The NMR for 9: H
NMR (CDCl3, 300 MHz) δ: 9.23 (s, 1H), 4.49 (s, 2H),
0.97 (t, J＝8.0 Hz, 9H), 0.65 (q, J＝7.9 Hz, 6H); 13C
NMR (CDCl3, 75 MHz) δ: 176.4, 94.8, 84.1, 51.1, 6.5,
4.2.
Chin. J. Chem. 2010, 28, 1635— 1639
© 2010 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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1637

Zhang & Wu
FULL PAPER
－1
n-BuLi (2.5 mol•L , in hexanes, 0.40 mL, 1.0 mmol)
was added dropwise to a solution of dry i-Pr2NH (0.14
mL, 1.01 mmol) in dry THF (3.0 mL) stirred at 0 ℃.
Stirring was continued at the same temperature for 15
min. The bath temperature was cooled to －78 ℃
before a solution of 8 (200 mg, 0.676 mmol) in dry THF
(1.0 mL) was introduced. The mixture was stirred at
－78 ℃ for another 15 min. A solution of the above
mentioned aldehyde 9 (200 mg, 1.01 mmol) in dry THF
(1.0 mL) was then added. The stirring was continued at
the same temperature for 1 h. Aq. sat. NH4Cl (10 mL)
was added, followed by water (10 mL). The mixture
was extracted with Et2O (20 mL×3), washed with wa-
ter and brine, and dried over anhydrous Na2SO4. Re-
moval of the solvent on a rotary evaporator and column
chromatography [V(PE)∶V(CH2Cl2)∶V(Et2O)＝3∶
3∶1] on silica gel afforded 10a and 10b (247 mg alto-
gether, 74% in total) as colorless oils.
mmol, 91%, which is more polar than 11a) as a color-
less oil. The epimer 11a was prepared from 10a in a
similar manner.
Data for 11a (less polar than 11b): [α] 2D7 ＋43.9 (c
1.0, CHCl3); 1H NMR (CDCl3, 400 MHz) δ: 7.68—7.64
(m, 2H), 7.47—7.44 (m, 3H), 6.80 (t, J＝5.2 Hz, 1H),
6.25 (t, J＝1.9 Hz, 1H), 4.73—4.59 (m, 2H), 4.27 (d,
J＝1.9 Hz, 2H), 1.57 (s, 3H), 0.95 (t, J＝7.8 Hz, 9H),
0.92 (s, 9H), 0.60 (q, J＝8.1 Hz, 6H), 0.10 (s, 6H); 13C
NMR (CDCl3, 100 MHz) δ: 168.4, 143.0, 139.4, 139.0,
131.4, 129.0, 126.0, 86.3, 78.6, 60.4, 57.3, 51.1, 25.8,
19.9, 18.2, 6.6, 4.3, －5.36, －5.38; FT-IR (film) ν:
3400, 2955, 2930, 2858, 2081, 1751, 1370, 1219, 1086,
1015, 837, 748 cm–1; ESI-MS m/z: 537.1 ([M＋H]＋);
ESI-HRMS calcd for C27H44Si2O5SNa 559.2340 ([M＋
Na]＋), found 559.2337.
Data for 11b (more polar than 11a): [α] 2D7 ＋29.6 (c
1.1, CHCl3); 1H NMR (CDCl3, 400 MHz) δ: 7.68—7.64
(m, 2H), 7.48—7.43 (m, 3H), 6.72 (t, J＝5.3 Hz, 1H),
6.19 (d, J＝2.0 Hz, 1H), 4.63 (ddd, J＝21.6, 16.0, 4.8,
2H), 4.00 (d, J＝1.8 Hz, 2H), 1.95 (s, 3H), 0.92 (s, 9H),
0.90 (t, J＝7.9 Hz, 9H), 0.54 (q, J＝7.7 Hz, 6H), 0.10 (s,
Data for 10a (the less polar isomer): [α] 2D7 ＋23.0 (c
1
0.97, CHCl3); H NMR (CDCl3, 300 MHz) δ: 7.71—
7.65 (m, 2H), 7.49—7.43 (m, 3H), 6.60 (t, J＝4.9 Hz,
1H), 5.06 (d, J＝7.6 Hz, 1H), 4.63 (dd, J＝15.6, 4.9 Hz,
1H), 4.57 (dd, J＝15.6, 5.1 Hz, 1H), 4.19—4.08 (m,
2H), 3.99 (d, J＝7.6 Hz, 1H), 0.93 (t, J＝8.2 Hz, 9H),
0.90 (s, 9H), 0.58 (q, J＝7.7 Hz, 6H), 0.11 (s, 6H); 13C
3H), 0.08 (s, 3H); 13C NMR (CDCl3, 100 MHz)
δ: 168.3,

142.3, 139.2, 139.2, 131.4, 129.0, 125.8, 85.5, 78.5,
60.5, 57.3, 50.8, 25.8, 20.4, 18.2, 6.5, 4.2, －5.38,
NMR (CDCl3, 75 MHz) δ: 143.7, 142.5, 135.2, 131.4,
129.0, 126.0, 84.6, 81.9, 60.5, 57.5, 51.0, 25.7, 18.2, 6.6,
4.2, －5.4, －5.6; FT-IR (film) ν: 3346, 2955, 2929,
2857, 2080, 1442, 1259, 1084, 1020, 836, 780 cm–1;
ESI-MS m/z: 495.1 ([M＋H]＋);＋ESI-HRMS calcd for
C25H43Si2O4S 495.2415 ([M＋H] ), found 495.2415.
Data for 10b (the more polar isomer): [α] 2D4 －16.9
－5.41; FT-IR (film) ν: 3393, 2955, 2928, 2856, 1752,
1372, 1257, 1219, 1＋084, 1020, 837, 779 cm–1; ESI-MS
m/z: 537.1 ([M＋H] ); ESI-HRMS calcd for C27H45Si2-
O5S 537.2521 ([M＋H]＋), found 537.2519.
(3aS)-1-(tert-Butyldimethylsilyloxy)-7-triethylsilyl-
oxy-hepta-2,3-dien-5-yne (12b) A solution of 11b
(25 mg, 0.0466 mmol) in dry THF (1.0 mL) was added
1
－1
(c 1.0, CHCl3); H NMR (CDCl3, 300 MHz) δ: 7.67—
to a solution of i-PrMgBr (2.5 mol•L , 0.11 mL, 0.28
7.61 (m, 2H), 7.50—7.44 (m, 3H), 6.57 (t, J＝4.9 Hz,
1H), 5.03 (dt, J＝6.2, 1.6 Hz, 1H), 4.67 (dd, J＝6.5, 4.9
Hz, 1H), 4.63 (dd, J＝6.5, 5.4 Hz, 1H), 4.41 (d, J＝6.4
Hz, 1H), 4.08 (d, J＝1.7 Hz, 2H), 0.91 (t, J＝7.7 Hz,
9H), 0.90 (s, 9H), 0.55 (q, J＝8.0 Hz, 6H), 0.11 (s, 3H),
mmol) in dry THF (1.5 mL) stirred at －100 ℃
(Et2O-liq. N2 bath) under argon. The mixture was stirred
at the same temperature for 15 min. Aq. sat. NH4Cl was
added. The mixture was extracted with Et2O (5 mL×3).
The combined organic layers were washed with water
and brine before being dried over anhydrous Na2SO4.
Removal of the solvent on a rotary evaporator and col-
umn chromatography [V(Et2O)∶V(PE)＝1∶75] on
silica gel afforded the known allene 12b2 (13 mg,
0.0373 mmol, 80%) as a colorless oil. [α] 2D4 ＋98.2 (c
0.6, CHCl3), of 87% ee [tR(major)＝11.65 min, tR(minor)
＝10.92 min] as determined by HPLC on a CHIRAL-
PAK OD column (0.46 cm×25.0 cm) eluting with
n-hexane at a flow rate of 0.7 mL/min with the UV de-
0.09 (s, 3H); 13C NMR (CDCl3, 75 MHz)
δ: 143.8,

141.8, 137.0, 131.3, 129.0, 125.6, 83.9, 82.2, 60.6, 56.5,
50.9, 25.8, 18.2, 6.6, 4.2, －5.4, －5.5; FT-IR (film) ν:
3344, 3053, 2954, 2861, 2081, 1645, 1463, 1257, 1084,
1019, 836, 746, 688 cm–1; ESI-MS m/z: 495.1 ([M＋
H]＋ ); ESI-HRMS calcd for C25H43Si2O4S 495.2415
([M＋H]＋), found 495.2420.
(3S)-3-Acetyloxy-7-tert-butyldimethylsilyloxy-5-
((S)-phenylsulfinyl)-1-triethylsilyloxy-hept-5-en-2-
yne (11b) To a solution of 10b (70 mg, 0.142 mmol)
in dry CH2Cl2 (1.5 mL) stirred in an ice-water bath were
added in turn Ac2O (44 µL, 0.426 mmol), pyridine (36
µL, 0.65 mmol) and DMAP (1.7 mg, 0.0142 mmol).
The stirring was then continued at ambient temperature
for 2 h. The mixture was diluted with Et2O (30 mL),
washed in turn with aq. sat. CuSO4, aq. sat. NH4Cl, aq.
sat. NaHCO3, and brine, and dried over anhydrous
Na2SO4. Removal of the solvent on a rotary evaporator
and column chromatography [V(PE)∶V(EtOAc)＝6∶1]
on silica gel afforded the acetate 11b (69 mg, 0.129
1
tector set to 214 nm. H NMR (CDCl3, 300 MHz) δ:
5.50 (dt, J＝6.4, 6.2 Hz, 1H), 5.49 (dt, J＝5.0, 3.4 Hz,
1H), 4.41 (s, 2H), 4.23 (dd, J＝5.1, 3.6 Hz, 2H), 0.98 (t,
J＝7.9 Hz, 9H), 0.90 (s, 9H), 0.65 (q, J＝7.9 Hz, 6H),
0.09 (s, 6H).
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