A facile stereoselective synthesis of (E)-α-silylyinyl sulfides via hydromagnesiation of alkynylsilanes

Article abstract of DOI:10.1002/hc.20165

Hydromagnesiation of alkynylsilanes 1 in diethyl ether gave (Z)-α-silylvinyl Grignard reagents 2, which reacted with arylsulfenyl chlorides 3 to afford stereoselectively (E)-α-silylvinyl sulfides 4 in good yields. (E)-α-Silylvinyl sulfides 4 could undergo

Full text of DOI:10.1002/hc.20165

Heteroatom Chemistry
Volume 16, Number 7, 2005
A Facile Stereoselective Synthesis
of (E )-α-Silylvinyl Sulfides via
Hydromagnesiation of Alkynylsilanes
Mingzhong Cai,1 Jun Xia,1 and Pingping Wang2
1Department of Chemistry, Jiangxi Normal University, Nanchang 330027, People’s Republic
of China
2Department of Chemistry, Jiujiang College, Jiujiang 332000, People’s Republic of China
Received 2 August 2005; revised 1 September 2005
diates; the difunctional group reagents containing
ABSTRACT: Hydromagnesiation of alkynylsilanes
sulfur and silicon have attracted special attention as
1 in diethyl ether gave ( Z)-ꢀ-silylvinyl Grignard
important intermediates in various synthetic trans-
reagents 2, which reacted with arylsulfenyl chlo-
formations since the silyl and thioether functions
rides 3 to afford stereoselectively (E)-ꢀ-silylvinyl sul-
exert an opposing polarization on the olefinic bond
fides 4 in good yields. (E)-ꢀ-Silylvinyl sulfides 4
[6–12]. However, few convenient routes to (E)-
could undergo the cross-coupling reactions with Grig-
2-alkyl-1-silylvinyl sulfides are known. For exam-
nard reagents in the presence of NiCl2(PPh3)2 to
ple, 1-trimethylsilyl vinyl sulfide has been synthe-
give stereoselectively (Z)-1,2-disubstituted vinylsilanes
sized by the addition of phenylsulfenyl chloride to
ꢀ
C
5.
2005 Wiley Periodicals, Inc. Heteroatom Chem
vinyltrimethylsilane followed by dehydrohalogena-
tion with DBU [6] or by the treatment of vinyl
sulfides with LDA, followed by the reaction with
chlorotrimethylsilane [7]. But these methods are not
applicable to the more highly substituted derivatives.
The chlorination of 1-phenylthio-1-silylalkanes fol-
lowed by dehydrochlorination afforded a mixture
of (E) and (Z)-2-alkyl-1-silylvinyl sulfides [8]. Some
other methods give (Z)-2-alkyl-1-silylvinyl sulfides
[9,10]. Recently, Zhong et al. [13] reported the stere-
oselective synthesis of (E)-2-alkyl-1-silylvinyl sulfides
via hydrozirconation of alkynylsilanes.
Hydromagnesiation has emerged as a unique
hydrometallation with some attractive features
such as the regioselectivity and stereoselectivity
observed with alkynylsilanes [14]. Very recently,
we have reported the stereoselective syntheses of
(E)-α-selenenylvinylsilanes [15] and (E)-α-aryltell-
urenylvinylsilanes [16] via hydromagnesiation of
alkynylsilanes. Herein, we wish to report that (E)-
α-silylvinyl sulfides could be conveniently synthe-
sized via the hydromagnesiation of alkynylsilanes,
followed by the reaction with arylsulfenyl chlorides.
16:644–647, 2005; Published online in Wiley InterScience
(www.interscience.wiley.com). DOI 10.1002/hc.20165
INTRODUCTION
Difunctional group reagents, which have two differ-
ent functional groups linked to the olefinic carbon
atoms, for example, S-Cu [1], S-B [2], S-Sn [3], Si-Sn
[4], and Si-Zr [5] combinations, play an important
role in organic synthesis, especially in developing
many convenient methods for the stereoselective
preparation of substituted alkenes. Both vinylsilanes
and vinyl sulfides are important synthetic interme-
Correspondence to: Mingzhong Cai; e-mail: caimzhong@163.
com.
Contract grant sponsor: National Natural Science Foundation
of China.
Contract grant number: 20462002.
Contract grant sponsor: Natural Science Foundation of Jiangxi
Province of China.
Contract grant number: 0420015.
2005 Wiley Periodicals, Inc.
c
ꢀ
644

A Facile Stereoselective Synthesis of (E)-ꢀ-Silylvinyl Sulfides via Hydromagnesiation of Alkynylsilanes 645
RESULTS AND DISCUSSION
this aim, a study of NiCl2(PPh3)2-catalyzed cross-
coupling of 4a and 4g with methylmagnesium bro-
mide was carried out; the corresponding (Z)-1,2-
disubstituted vinylsilanes 5 were obtained in good
yields according to Scheme 2.
Vinylsilanes have been widely utilized in the syn-
thesis of natural products [20], by coupling with
electrophiles such as acyl halides [21], alkenyl or
aryl halides [22] as well as arenediazonium ion [23].
Therefore, (E)-α-silylvinyl sulfides 4 can be regarded
as the equivalent of the cation–anion synthon 6.
Alkynylsilanes 1 were prepared according to the liter-
ature procedure [17]. Hydromagnesiation of alkynyl-
silanes 1 at 25◦C in diethyl ether for 6 h gave (Z)-α-
silylvinyl Grignard reagents 2, which reacted with
arylsulfenyl chlorides 3 to afford stereoselectively
(E)-α-silylvinyl sulfides 4 in good yields (Scheme 1).
The typical results are summarized in Table 1.
1
Investigations of the crude products 4 by H-
NMR spectroscopy (400 MHz) showed their isomeric
purities by more than 97%. One olefinic proton sig-
nal of compounds 4a–i splits characteristically into
one triplet at δ = 6.23–6.58 with coupling constant
J = 7.6 Hz, which indicated that the hydromagnesia-
tion to the alkynylsilanes had taken place with strong
preference for the addition of the magnesium atom
at the carbon adjacent to the silyl group.
(E)-α-Silylvinyl sulfides 4 are difunctional group
reagents in which two synthetically versatile groups
are linked to the same olefinic carbon atom and can
be considered both as vinyl sulfides and vinylsilanes.
It is known that vinyl sulfides couple with Grignard
reagents in the presence of nickel(II)-phosphine
complexes to give olefins, with predominant reten-
tion of configuration [18]. Phenyl vinyl sulfides con-
taining a trimethylsilyl group in the ꢁ-position were
coupled with Grignard reagents to synthesize stere-
ospecifically monosubstituted E-vinylsilanes [19].
(Z)-ꢀ- Silylvinyl sulfides were coupled with Grignard
reagents in the presence of NiCl2(PPh3)2 to give stere-
oselectively (E)-1,2-disubstituted vinylsilanes [10].
(E)-α- Silylvinyl sulfides 4 could, in principle, afford
(Z)-1,2-disubstituted vinylsilanes 5 (Scheme 2). With
In summary, we have developed a new route
to stereoselective synthesis of (E)-α-silylvinyl sul-
fides. Compared to the reported method [13], the
present method has advantages of readily available
and cheap starting materials instead of the expensive
Cp2Zr(H)Cl, straightforward and simple procedures,
mild reaction conditions, and good yields.
EXPERIMENTAL
Diethyl ether was distilled from sodium immedi-
ately prior to use. THF was freshly distilled from
sodium-benzophenone prior to its use. IR spectra
were obtained on a Perkin-Elmer 683 instrument
1
as neat films. H-NMR spectra were recorded on a
Bruker AC-400 (400 MHz) spectrometer using CDCl3
SCHEME 1
TABLE 1 Synthesis of (E )-α-Silylvinyl Sulfides 4a–i
Entry
R
Ar
Product
Yield(%)a
1
2
3
4
5
6
7
8
9
n-C4H9
n-C4H9
n-C4H9
i -C5H
Ph
4a
4b
4c
4d
4e
4f
4g
4h
4i
76
70
73
67
71
66
62
69
65
4-CH3C6H4
4-ClC6H4
4-CH3C6H4
4-ClC6H4
Ph
4-CH3C6H4
4-ClC6H4
Ph
i -C5H11
11
n-C6H
n-C6H
n-C6H
13
13
13
PhCH2
aIsolated yield based on the arylsulfenyl chloride 3 used.

646 Cai, Xia, and Wang
SCHEME 2
as solvent. Mass spectra were determined on a Finni-
gan 8230 mass spectrometer. Microanalyses were
measured using a Yanaco MT-3 CHN microelemen-
tal analyzer. Arylsulfenyl chlorides 3 were prepared
according to the literature method [24]. Methylmag-
nesium bromide was purchased from Aldrich, and
NiCl2(PPh3)2 was prepared according to the proce-
dure described by Venanzi [25].
3H), 2.25–2.17 (m, 2H), 1.38–1.20 (m, 4H), 0.89 (t,
J= 7.2 Hz, 3H), 0.15 (s, 9H); MS: m/z 278 (M+, 13),
263 (29), 187 (22), 91 (31), 73 (100); Anal. found: C,
68.78; H, 9.19. C16H26SiS calcd: C, 69.06; H, 9.35.
(E)-1-(4-Chlorophenyl)sulfanyl-1-trimethylsilyl-
1-hexene 4c. IR (film): ꢂ (cm−1) 3076, 2956, 2928,
2873, 1576, 1474, 1389, 1249, 1093, 1012, 839, 735;
1H NMR (CDCl3): δ 7.07 (d, J = 8.0 Hz, 2H), 7.02 (d,
J = 8.0 Hz, 2H), 6.39 (t, J = 7.6 Hz, 1H), 2.15–2.07
(m, 2H), 1.28–1.18 (m, 4H), 0.78 (t, J = 7.2 Hz, 3H),
−0.01 (s, 9H); MS: m/z 299 (M+, 10.5), 284 (47),
187 (29), 73 (100); Anal. found: C, 60.25; H, 7.53.
C15H23ClSiS calcd: C, 60.20; H, 7.69.
General Procedure for the Synthesis
of (E)-ꢀ-Silylvinyl Sulfides 4a–i
To
a solution of isobutylmagnesium bromide
(2.5 mmol) in diethyl ether (4 mL) was added
Cp2TiCl2 (25 mg, 0.1 mmol) at 0◦C under Ar, and
the mixture was stirred for 30 min at that temper-
ature. To this solution was added alkynylsilane 1
(2.0 mmol), and the mixture was stirred for 6 h
at 25◦C. After being cooled to 0◦C a solution of
arylsulfenyl chloride 3 (1.5 mmol) in Et2O (2 mL)
was added dropwise over 30 min with stirring, and
the mixture was stirred for 2 h at 25◦C, quenched
with sat. aq. NH4Cl (15 mL) and extracted with Et2O
(2 × 30 mL). The organic layer was washed with sat.
aq. NH4Cl (20 mL) and water (3 × 20 mL) and dried
(MgSO4). Removal of the solvent under reduced pres-
sure gave an oil, which was purified by column chro-
matography on silica gel using light petroleum as
eluent.
(E)-1-(4-Methylphenyl)sulfanyl-1-trimethylsilyl-
5-methyl-1-thexene 4d. IR (film): ꢂ (cm−1) 3071,
3019, 2956, 2869, 1578, 1490, 1467, 1384, 1249, 839,
1
806, 757; H NMR (CDCl3): δ 7.04 (d, J = 8.0 Hz,
2H), 6.95 (d, J = 8.0 Hz, 2H), 6.23 (t, J = 7.6 Hz,
1H), 2.18 (s, 3H), 2.14–2.07 (m, 2H), 1.46–1.41 (m,
1H), 1.18–1.10 (m, 2H), 0.78 (d, J = 6.8 Hz, 6H),
0.03 (s, 9H); MS: m/z 292 (M+, 8.3), 277 (47), 201
(35), 91 (25), 73 (100); Anal. found: C, 69.59; H, 9.42.
C17H28SiS calcd: C, 69.86; H, 9.59.
(E)-1-(4-Chlorophenyl)sulfanyl-1-trimethylsilyl-
5-methyl-1-hexene 4e. IR (film): ꢂ (cm−1) 3076,
2958, 2870, 1630, 1577, 1474, 1385, 1249, 1092,
1
1012, 870, 840, 816, 756; H NMR (CDCl3): δ 7.09
(E)-1-Phenylsulfanyl-1-trimethylsilyl-1-hexene
(d, J = 8.0 Hz, 2H), 7.02 (d, J = 8.0 Hz, 2H), 6.38 (t,
J = 7.6 Hz, 1H), 2.15–2.08 (m, 2H), 1.46–1.39 (m,
1H), 1.18-1.11 (m, 2H), 0.76 (d, J = 6.8 Hz, 6H), 0.01
(s, 9H); MS: m/z 313 (M+, 14), 298 (40), 201 (26),
73 (100); Anal. found: C, 61.07; H, 7.80. C16H25ClSiS
calcd: C, 61.34; H, 7.99.
4a. IR (film): ꢂ (cm−1) 3070, 3051, 2960, 2865,
1
1585, 1481, 1456, 1250, 1020, 840, 742; H NMR
(CDCl3): δ 7.28–7.14 (m, 5H), 6.52 (t, J = 7.6 Hz, 1H),
2.28–2.20 (m, 2H), 1.41–1.28 (m, 4H), 0.92 (t, J =
7.2 Hz, 3H), 0.14 (s, 9H); MS: m/z 264 (M+, 17.2),
249 (33), 207 (26), 187 (27), 77 (19), 73 (100); Anal.
found: C, 67.89; H, 8.85. C15H24SiS calcd: C, 68.18;
H, 9.09.
(E)-1-Phenylsulfanyl-1-trimethylsilyl-1-octene 4f.
IR (film): ꢂ (cm−1) 3070, 3022, 2959, 2920, 2865,
1
1579, 1490, 1468, 1249, 1020, 839, 740; H NMR
(E)-1-(4-Methylphenyl)sulfanyl-1-trimethylsilyl-
1-hexene 4b. IR (film): ꢂ (cm−1) 3071, 3019, 2958,
2925, 1580, 1491, 1464, 1382, 1248, 839, 805, 756;
1H NMR (CDCl3): δ 7.16 (d, J = 8.0 Hz, 2H), 7.07 (d,
J = 8.0 Hz, 2H), 6.36 (t, J = 7.6 Hz, 1H), 2.30 (s,
(CDCl3): δ 7.26–7.14 (m, 5H), 6.51 (t, J = 7.6 Hz,
1H), 2.26–2.19 (m, 2H), 1.46–1.25 (m, 8H), 0.89 (t,
J = 7.2 Hz, 3H), 0.14 (s, 9H); MS: m/z 292 (M+, 6.7),
277 (39), 215 (23), 77 (34), 73 (100); Anal. found: C,
69.57; H, 9.62. C17H28SiS calcd: C, 69.86; H, 9.59.

A Facile Stereoselective Synthesis of (E)-ꢀ-Silylvinyl Sulfides via Hydromagnesiation of Alkynylsilanes 647
(E)-1-(4-Methylphenyl)sulfanyl-1-trimethylsilyl-
3H), 0.11 (s, 9H); Anal. found: C, 70.36; H, 12.79.
C10H22Si calcd: C, 70.59; H, 12.94.
1-octene 4g. IR (film): ꢂ (cm−1) 3072, 3019, 2956,
2923, 1579, 1491, 1456, 1249, 840, 806, 758; 1H
NMR (CDCl3): δ 7.17 (d, J = 8.0 Hz, 2H), 7.08 (d, J=
8.0 Hz, 2H), 6.37 (t, J = 7.6 Hz, 1H), 2.31 (s, 3H),
2.25–2.18 (m, 2H), 1.43–1.22 (m, 8H), 0.91 (t, J =
7.2 Hz, 3H), 0.16 (s, 9H); MS: m/z 306 (M+, 16),
291 (43), 215 (30), 91 (27), 73 (100); Anal. found: C,
70.33; H, 9.74. C18H30SiS calcd: C, 70.59; H, 9.81.
(Z)-2-Trimethylsilyl-2-nonene. IR
(film):
ꢂ
1
(cm−1) 2926, 2856, 1607, 1458, 1248, 837; H NMR
(CDCl3): δ 5.81 (t, J = 7.2 Hz, 1H), 2.17–2.03 (m,
2H), 1.73 (s, 3H), 1.47–1.22 (m, 8H), 0.88 (t, J =
7.2 Hz, 3H), 0.11 (s, 9H); Anal. found: C, 72.51; H,
13.02. C12H26Si calcd: C, 72.73; H, 13.13.
(E)-1-(4-Chlorophenyl)sulfanyl-1-trimethylsilyl-
1-octene 4h. IR (film): ꢂ (cm−1) 3067, 3022, 2957,
2928, 2857, 1577, 1474, 1388, 1249, 1093, 839, 759,
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696; H NMR (CDCl3): δ 7.22 (d, J = 8.0 Hz, 2H),
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A 3.0 M THF solution of MeMgBr (15 mmol) was
slowly added, under Ar, to a stirred suspension of
NiCl2(PPh3)2 (0.03 mmol) and the (E)-ꢀ-silylvinyl sul-
fide 4 (1 mmol) in THF (6 mL) at room temperature.
The mixture was stirred at reflux temperature for
48 h. After being cooled to room temperature, the
mixture was quenched with sat. aq. NH4Cl (15 mL)
and extracted with Et2O (2 × 30 mL). The organic
layer was washed with water (3 × 10 mL) and dried
(MgSO4). Removal of the solvent under reduced pres-
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ꢂ
(cm−1) 2958, 2860, 1620, 1466, 1249, 838; H NMR
(CDCl3): δ 5.84 (t, J = 7.2 Hz, 1H), 2.16–2.05 (m, 2H),
1.74 (s, 3H), 1.37–1.21 (m, 4H), 0.89 (t, J = 7.2 Hz,
1
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