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

Article abstract of DOI:10.1016/j.jorganchem.2004.07.063

(E)-α-Silylvinylstannanes have been synthesized by the hydromagnesiation reaction of alkynylsilanes, followed by the reaction with trialkylstannyl chlorides. (E)-α-Silylvinylstannanes can undergo the cross-coupling reaction with aryl iodides in the presence of a catalytic amounts of Pd(PPh₃)₄ and CuI to afford (Z)-1,2-disubstituted vinylsilanes in good yields.

Full text of DOI:10.1016/j.jorganchem.2004.07.063

Journal of Organometallic Chemistry 689 (2004) 3593–3597
www.elsevier.com/locate/jorganchem
A facile stereoselective synthesis of (E)-a-silylvinylstannanes via
hydromagnesiation of alkynylsilanes
a,
a
b
a
Mingzhong Cai *, Wenyan Hao , Hong Zhao , Jun Xia
a
Institute of Chemistry, Jiangxi Normal University, Nanchang 330027, PR China
b
Department of Pharmacy, Guangdong Pharmaceutical College, Guangzhou 510240, PR China
Received 15 March 2004; accepted 7 July 2004
Available online 11 September 2004
Abstract
(E)-a-Silylvinylstannanes have been synthesized by the hydromagnesiation reaction of alkynylsilanes, followed by the reaction
with trialkylstannyl chlorides. (E)-a-Silylvinylstannanes can undergo the cross-coupling reaction with aryl iodides in the presence
of a catalytic amounts of Pd(PPh3)4 and CuI to afford (Z)-1,2-disubstituted vinylsilanes in good yields.
ꢀ 2004 Elsevier B.V. All rights reserved.
Keywords: Hydromagnesiation; Alkynylsilane; (E)-a-Silylvinylstannane; Cross-coupling reaction; Stereoselective synthesis
1. Introduction
ported. Vinylsilanes are also important synthetic inter-
mediates [13], but the difunctional group reagent
containing tin and silicon has rarely aroused extensive
attention. Mitchell et al. [14] described that the alkynes
underwent the regio- and stereospecific addition with
(trimethylsilyl)trialkylstannanes in the presence of
Pd(PPh3)4 catalyst to give (Z)-b-silylvinylstannanes.
Hydromagnesiation has emerged as a unique hydrome-
tallation with some attractive features such as the high
regioselectivity and stereoselectivity observed with
alkynylsilanes [15]. We now wish to report that (E)-a-
silylvinylstannanes could be synthesized by hydromag-
nesiation of alkynylsilanes, followed by treatment with
trialkylstannyl chlorides (Scheme 1).
Methodologies for the stereoselective synthesis of
vinylstannanes are of considerable interest because the
vinylstannanes are proven synthons and very useful
building blocks in synthetic organic chemistry [1]. Due
to their synthetic utility, a variety of methods have been
developed for their preparation including those involv-
ing carbonyl addition chemistry [2]; transmetallation
of vinylmetallic species [3]; metallometallation of alky-
nes [4]; and the hydrostannylation of alkynes induced
by either radical initiators [5] or Lewis acid [6] or transi-
tion metal catalysts [7]. Difunctional group reagents,
which have two different functional groups linked to
the olefinic carbon atoms, for example, Sn–Al [8], Sn–
Cu [9], Sn–Mg [10], Sn–Zr [11] and Sn–Se [12] combina-
tions, play an important role in organic synthesis,
especially in developing many convenient methods for
the stereoselective synthesis of substituted alkenes. These
reagents and their synthetic applications have been re-
2. Results and discussion
Alkynylsilanes 1 were prepared according to the
literature procedure [16]. Hydromagnesiation of alkynyl-
silanes 1 at 25 ꢁC in diethyl ether for 6 h gave (Z)-a-
silylvinyl Grignard reagents 2, which reacted with
tributylstannyl chloride or trimethylstannyl chloride 3
*
Corresponding author. Fax: +86 791 8517500.
E-mail address: caimingz@tom.com (M. Cai).
0022-328X/$ - see front matter ꢀ 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2004.07.063

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M. Cai et al. / Journal of Organometallic Chemistry 689 (2004) 3593–3597
1
R
SnCl (3)
SiMe3
R
H
SiMe3
MgBr
3
R
H
Cp TiCl (5 mol%)
2
2
R
SiMe3 i-BuMgBr
+
SnR1
Et O or THF
2
Et O, 25˚C
3
2
-MgBrCl
4
2
1
Scheme 1.
SiMe3
H
n-C4H9
H
at room temperature for 4 h to afford (E)-a-silylvinyl-
stannanes 4 in high yields. The intermediates 2 were
found to possess low reactivity with triphenylstannyl
chloride and the Mg/Sn metathesis reaction did not
occur in diethyl ether at 30 ꢁC. However, the Mg/Sn
metathesis reaction proceeded smoothly in THF at
60 ꢁC and the corresponding (E)-a-silylvinylstannanes
4 were obtained in good yields (Entry 3, 6, 9) after
8 h. The typical results are summarized in Table 1.
The hydromagnesiation of alkynylsilanes 1 at 25 ꢁC
in ether is almost 100% regio-and stereoselective as pre-
viously described [15]. We observed that the Mg/Sn
metathesis reaction on intermediates 2 occurs with total
retention of the configuration. Investigations of the
crude products 4 by 1H NMR spectroscopy (400
MHz) showed their isomeric purities to be more than
98%, one olefinic proton signal of 4a–j splits character-
istically into one triplet with a coupling constant of
J = 6.9 Hz, which indicated that the hydromagnesiation
of alkynylsilanes had taken place with strong preference
for the addition of the magnesium atom at the carbon
adjacent to the silyl group. The configuration of com-
pound 4a could be confirmed from compound 5 which
was obtained by treatment of 4a with n-butyllithium in
THF followed by hydrolysis, a reaction which occurs
stereoselectively (Scheme 2) [17]. The stereochemistry
SiMe3
SnBu3
n-C4H9
H
1. -78˚C , BuLi/THF
2. H O
2
5
4a
Scheme 2.
SiMe3
SnR1
SiMe3
Ar
R
H
R
Pd(PPh ) /CuI
3 4
+
ArI
DMF, r.t., 48 h
H
3
6
4
Scheme 3.
Table 2
Synthesis of (Z)-1,2-disubstituted vinylsilanes 6 according to Scheme 3
Entry
R
R1
Ar
Product
Yielda (%)
1
2
3
4
5
a
n-C4H9
n-C4H9
i-C5H11
n-C6H13
PhCH2
CH3
CH3
Ph
6a
6b
6c
6d
6e
78
83
71
84
75
4-ClC6H4
4-ClC6H4
Ph
n-C4H9
CH3
n-C4H9
Ph
Isolated yield based on the 4 used.
1
of compound 5 was easily established, since H NMR
when (E)-a-silylvinylstannanes 4 were allowed to react
with aryl iodides in the presence of a catalytic amounts
of Pd(PPh3)4 and CuI in DMF at room temperature un-
der Ar, the corresponding (Z)-1,2-disubstituted vinylsi-
lanes 6 were obtained in good yields according to
Scheme 3 and Table 2.
spectrum (400 MHz) of 5 gives rise to a doublet at
d = 5.44 with a coupling constant of 11.5 Hz, which is
consistent with an Z-configuration.
We have also carried out the cross-coupling reaction
of compounds 4 with aryl iodides. We observed that
In summary, our results showed that the hydromag-
nesiation–stannylation sequence of the alkynylsilanes
has the advantages of readily available starting materi-
als, straightforward and simple procedures, mild reac-
tion conditions and high yields. The investigation on
the synthetic applications of compounds 4 is in progress.
Table 1
Synthesis of (E)-a-silylvinylstannanes 4a–j
Entry
R
R1
Producta
Yield (%)b
1
2
n-C4H9
n-C4H9
n-C4H9
i-C5H11
i-C5H11
i-C5H11
n-C6H13
n-C6H13
n-C6H13
PhCH2
n-C4H9
CH3
Ph
4a
4b
4c
4d
4e
4f
90
87
69
89
86
72
88
85
70
81
3
4
n-C4H9
CH3
Ph
5
3. Experimental
6
1H and 13C NMR spectra were recorded in CDCl3 on
a Bruker AC 400 MHz spectrometer with TMS as an
internal standard. Chemical shifts are given in ppm
and spin–spin coupling constants, J, are given in Hz.
IR spectra were obtained on a Perkin–Elmer 683 instru-
ment as neat films. Mass spectra were determined on a
7
n-C4H9
CH3
Ph
4g
4h
4i
8
9
10
a
n-C4H9
4j
All the compounds 4 were characterized by IR, 1H NMR,
13C NMR, MS and elemental analyses.
b
Isolated yield based on the trialkylstannyl chloride used.

M. Cai et al. / Journal of Organometallic Chemistry 689 (2004) 3593–3597
3595
Finnigan 8230 mass spectrometer. Microanalyses were
measured using a Yanaco MT-3 CHN microelemental
analyzer. All solvents were dried, deoxygenated and
freshly distilled before use.
3.1.4. (E)-1-Trimethylsilyl-1-trimethylstannyl-5-methyl-
1-hexene (4e)
IR (film): m (cmÀ1) 2958, 2925, 2872, 1571, 1465,
1
1440, 1384, 1367, 856, 839. H NMR: d 6.51 (t, J = 6.9
Hz, 1H), 2.25–2.19 (m, 2H), 1.65–1.56 (m, 1H), 1.34–
1.28 (m, 2H), 0.92 (d, J = 6.8 Hz, 6H), 0.21 (s, 9H),
0.16 (s, 9H). 13C NMR: d 158.43, 141.92, 38.23, 34.63,
27.88, 22.59, 1.53, À8.02. MS: m/z 333 (M+, 9.8), 73
(100). Anal. Found: C, 46.62; H, 8.79. C13H30SiSn Calc.:
C, 46.85; H, 9.01%.
3.1. General procedure for the synthesis of (E)-a-silylvi-
nylstannanes 4a, 4b, 4d, 4e, 4g, 4h, 4j
To a solution of isobutylmagnesium bromide (4.5
mmol) in Et2O (7 ml) was added Cp2TiCl2 (50 mg, 0.2
mmol) at 0 ꢁC under Ar, and the mixture was stirred
for 30 min at that temperature. To this solution was
added alkynylsilane 1 (4.0 mmol), and the mixture was
stirred for 6 h at 25 ꢁC. After being cooled to 0 ꢁC, a
solution of trialkylstannyl chloride 3 (3.0 mmol) in
Et2O (2 ml) was added and the mixture was stirred at
room temperature for 4 h, quenched with saturated
aqueous NH4Cl (25 ml) and extracted with Et2O
(2 · 40 ml). The organic layer was washed with satu-
rated aqueous NH4Cl (25 ml) and H2O (3 · 30 ml)
and dried (MgSO4). Removal of solvent under reduced
pressure gave an oil, which was purified by column chro-
matography on silica gel using light petroleum ether (bp
30–60 ꢁC) as eluent.
3.1.5. (E)-1-Trimethylsilyl-1-tributylstannyl-1-octene (4g)
IR (film): m (cmÀ1) 2954, 2926, 2872, 2855, 1567,
1
1464, 1247, 856, 835. H NMR: d 6.48 (t, J = 6.9 Hz,
1H), 2.25–2.16 (m, 2H), 1.52–1.29 (m, 20H), 0.95–0.82
(m, 18H), 0.13 (s, 9H). 13C NMR: d 159.10, 141.15,
36.83, 31.84, 29.62, 29.20, 29.03, 27.38, 22.62, 14.04,
13.68, 10.49, 1.50. MS: m/z 473 (M+, 1.8), 73 (100).
Anal. Found: C, 58.12; H, 10.41. C23H50SiSn Calc.: C,
58.35; H, 10.57%.
3.1.6. (E)-1-Trimethylsilyl-1-trimethylstannyl-1-octene
(4h)
IR (film): m (cmÀ1) 2924, 2856, 1567, 1462, 1376,
1
1248, 839. H NMR: d 6.51 (t, J = 6.9 Hz, 1H), 2.26–
3.1.1.
(4a)
(E)-1-Trimethylsilyl-1-tributylstannyl-1-hexene
2.17 (m, 2H), 1.41–1.25 (m, 8H), 0.90 (t, J = 6.8 Hz,
3H), 0.15 (s, 9H), 0.12 (s, 9H). 13C NMR: d 158.39,
141.76, 36.65, 31.80, 29.56, 29.12, 22.60, 14.06, 1.54,
À8.01. MS: m/z 347 (M+, 8.2), 73 (100). Anal. Found:
C, 48.19; H, 9.04. C14H32SiSn Calc.: C, 48.42; H, 9.22%.
IR (film): m (cmÀ1) 2955, 2926, 2871, 1567, 1464,
1
1376, 1246, 858, 834. H NMR: d 6.47 (t, J = 6.9 Hz,
1H), 2.25–2.15 (m, 2H), 1.49–1.29 (m, 16H), 0.95–0.82
(m, 18H), 0.12 (s, 9H). 13C NMR: d 159.20, 141.17,
36.37, 31.84, 29.25, 27.38, 22.53, 14.06, 13.68, 10.47,
1.53. MS: m/z 445 (M+, 3.7), 73 (100). Anal. Found:
C, 56.44; H, 10.15. C21H46SiSn Calc.: C, 56.63; H,
10.34%.
3.1.7. (E)-1-Trimethylsilyl-1-tributylstannyl-3-phenyl-1-
propene (4j)
IR (film): m (cmÀ1) 3061, 3018, 2955, 2853, 1579,
1492, 1464, 839, 730, 690. 1H NMR: d 7.43–6.94
(m, 5H), 6.51 (t, J = 6.9 Hz, 1H), 3.56 (d, J = 7.2
Hz, 2H), 1.47–1.29 (m, 12 H), 0.93–0.82 (m, 15H),
0.13 (s, 9H). 13C NMR: d 159.21, 140.22, 130.17,
129.11, 128.40, 126.04, 39.55, 29.05, 27.32, 13.63,
9.87, 0.75. MS: m/z 479 (M+, 1.4), 73 (100). Anal.
Found: C, 59.87; H, 9.24. C24H44SiSn Calc.: C,
60.13; H, 9.19%.
3.1.2. (E)-1-Trimethylsilyl-1-trimethylstannyl-1-hexene
(4b)
IR (film): m (cmÀ1) 2924, 2855, 1568, 1465, 1378,
1
1248, 839. H NMR: d 6.51 (t, J = 6.9 Hz, 1H), 2.26–
2.19 (m, 2H), 1.45–1.29 (m, 4H), 0.93 (t, J = 7.2 Hz,
3H), 0.15 (s, 9H), 0.12 (s, 9H). 13C NMR: d 158.33,
141.78, 36.35, 31.73, 22.52, 14.07, 1.54, À8.01. MS: m/
z 319 (M+, 8.4), 73 (100). Anal. Found: C, 44.96; H,
8.62. C12H28SiSn Calc.: C, 45.14; H, 8.78%.
3.2. General procedure for the synthesis of (E)-a-silylvi-
nylstannanes 4c, 4f, 4i
3.1.3. (E)-1-Trimethylsilyl-1-tributylstannyl-5-methyl-1-
hexene (4d)
To a solution of isobutylmagnesium bromide (4.5
mmol) in Et2O (7 ml) was added Cp2TiCl2 (50 mg, 0.2
mmol) at 0 ꢁC under Ar, and the mixture was stirred
for 30 min at that temperature. To this solution was
added alkynylsilane 1 (4.0 mmol), and the mixture was
stirred for 6 h at 25 ꢁC. After removal of the Et2O under
reduced pressure (2 h, r.t./2 Torr), the residue was dis-
solved in THF (6 ml), and a solution of Ph3SnCl (3.0
mmol) in THF (4 ml) was added and the reaction
mixture was stirred at 60 ꢁC for 8 h, quenched with
IR (film): m (cmÀ1) 2955, 2926, 2872, 1567, 1465,
1
1384, 1366, 1247, 1071, 856, 834. H NMR: d 6.48 (t,
J = 6.9 Hz, 1H), 2.25–2.16 (m, 2H), 1.61–1.27 (m,
15H), 0.95–0.83 (m, 21H), 0.13 (s, 9H). 13C NMR: d
159.11, 140.94, 38.90, 34.87, 29.20, 27.99, 27.38, 22.61,
13.69, 10.48, 1.50. MS: m/z 459 (M+, 4.2), 73 (100).
Anal. Found: C, 57.31; H, 10.27. C22H48SiSn Calc.: C,
57.52; H, 10.46%.

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M. Cai et al. / Journal of Organometallic Chemistry 689 (2004) 3593–3597
saturated aqueous NH4Cl (25 ml) at 0 ꢁC and extracted
with Et2O (2 · 40 ml). The organic layer was washed
with saturated aqueous NH4Cl (25 ml) and H2O
(3 · 30 ml) and dried (MgSO4). Removal of solvent un-
der reduced pressure gave an oil, which was purified by
column chromatography on silica gel using light petro-
leum ether (bp 30–60 ꢁC) as eluent.
tography on silica gel eluting with light petroleum (30–
60 ꢁC).
3.3.1. (Z)-1-Trimethylsilyl-1-phenyl-1-hexene (6a)
IR (film): m (cmÀ1) 2956, 2858, 1602, 1598, 1489,
1249, 839. 1H NMR: d 7.40–6.91 (m, 5H), 6.01 (t,
J = 7.0 Hz, 1H), 2.35–2.17 (m, 2H), 1.49–1.23 (m,
4H), 0.91 (t, J = 7.1 Hz, 3H), 0.12 (s, 9H). Anal.
Found: C, 77.31; H, 10.25. C15H24Si Calc.: C, 77.59;
H, 10.34%.
3.2.1. (E)-1-Trimethylsilyl-1-triphenylstannyl-1-hexene
(4c)
IR (film): m (cmÀ1) 3064, 3015, 2954, 2871, 2858,
1639, 1568, 1480, 1428, 1247, 1073, 836, 727, 700. H
1
3.3.2. (Z)-1-Trimethylsilyl-1-(4-chlorophenyl)-1-hexene
(6b)
NMR: d 7.53–7.24 (m, 15H), 6.60 (t, J = 6.9 Hz, 1H),
2.27–2.19 (m, 2H), 1.36–1.18 (m, 4H), 0.89 (t, J = 7.2
Hz, 3H), 0.18 (s, 9H). 13C NMR: d 164.17, 140.34,
137.43, 137.08, 128.73, 128.39, 36.87, 31.71, 22.58,
14.09, 1.70. MS: m/z 505 (M+, 1.4), 73 (100). Anal.
Found: C, 63.93; H, 6.56. C27H34SiSn Calc.: C, 64.16;
H, 6.73%.
IR (film): m (cmÀ1) 2957, 2858, 1605, 1597, 1485,
1
1249, 839. H NMR: d 7.08 (d, J = 8.8 Hz, 2H), 6.78
(d, J = 8.8 Hz, 2H), 5.94 (t, J = 7.0 Hz, 1H), 2.32–2.18
(m, 2H), 1.47–1.25 (m, 4H), 0.90 (t, J = 7.2 Hz, 3H),
0.15 (s, 9H). Anal. Found: C, 67.66; H, 8.56. C15H23SiCl
Calc.: C, 67.54; H, 8.63%.
3.2.2. (E)-1-Trimethylsilyl-1-triphenylstannyl-5-methyl-
1-hexene (4f)
3.3.3. (Z)-1-Trimethylsilyl-1-(4-chlorophenyl)-5-methyl-
1-hexene (6c)
IR (film): m (cmÀ1) 3064, 3016, 2955, 2869, 1639,
1568, 1480, 1429, 1384, 1366, 1248, 838, 727, 699. H
IR (film): m (cmÀ1) 2955, 2870, 1606, 1486, 1384,
1
1
1366, 1249, 838. H NMR: d 7.06 (d, J = 8.8 Hz, 2H),
NMR: d 7.49–7.22 (m, 15H), 6.57 (t, J = 6.9 Hz, 1H),
2.29–2.18 (m, 2H), 1.50–1.36 (m, 1H), 1.20–1.13 (m,
2H), 0.87 (d, J = 6.4 Hz, 6H), 0.15 (s, 9H). 13C NMR:
d 164.30, 140.35, 137.46, 137.11, 128.77, 128.44, 38.71,
35.26, 28.22, 22.67, 1.74. MS: m/z 519 (M+, 2.2), 73
(100). Anal. Found: C, 64.51; H, 6.85. C28H36SiSn Calc.:
C, 64.74; H, 6.94%.
6.74 (d, J = 8.8 Hz, 2H), 5.91 (t, J = 7.0 Hz, 1H),
2.34–2.16 (m, 2H), 1.67–1.23 (m, 3H), 0.91 (d, J = 6.4
Hz, 6H), 0.13 (s, 9H). Anal. Found: C, 68.61; H, 8.99.
C16H25SiCl Calc.: C, 68.45; H, 8.91%.
3.3.4. (Z)-1-Trimethylsilyl-1-phenyl-1-octene (6d)
IR (film): m (cmÀ1) 2955, 2855, 1602, 1573, 1488,
1249, 837. 1H NMR: d 7.36–6.97 (m, 5H), 5.98 (t,
J = 7.0 Hz, 1H), 2.41–2.19 (m, 2H), 1.59–1.21 (m, 8H),
0.90 (t, J = 7.1 Hz, 3H), 0.11 (s, 9H). Anal. Found: C,
78.22; H, 10.53. C17H28Si Calc.: C, 78.46; H, 10.77%.
3.2.3. (E)-1-Trimethylsilyl-1-triphenylstannyl-1-octene
(4i)
IR (film): m (cmÀ1) 3064, 3016, 2927, 2855, 1638,
1570, 1480, 1429, 1247, 1074, 835, 727, 700. H NMR:
1
d 7.63–7.35 (m, 15H), 6.65 (t, J = 6.9 Hz, 1H), 2.29–
2.19 (m, 2H), 1.40–1.19 (m, 8H), 0.84 (t, J = 7.2 Hz,
3H), 0.16 (s, 9H). 13C NMR: d 164.26, 140.36, 137.36,
137.11, 128.76, 128.23, 37.14, 31.63, 29.18, 28.89,
22.53, 14.09, 1.68. MS: m/z 533 (M+, 1.7), 73 (100).
Anal. Found: C, 65.04; H, 7.21. C29H38SiSn Calc.: C,
65.29; H, 7.13%.
3.3.5. (Z)-1-Trimethylsilyl-1,3-diphenyl-1-propene (6e)
IR (film): m (cmÀ1) 2958, 2860, 1605, 1596, 1490,
1249, 839. 1H NMR: d 7.46–6.87 (m, 10H), 5.96 (t,
J = 7.0 Hz, 1H), 3.52 (d, J = 7.2 Hz, 2H), 0.12 (s, 9H).
Anal. Found: C, 81.07; H, 8.11. C18H22Si Calc.: C,
81.20; H, 8.27%.
3.3. General procedure for the synthesis of (Z)-1,2-
disubstituted vinylsilanes (6a–e)
Acknowledgements
Project 20062002 was supported by the National Nat-
ure Science Foundation of China and this work was also
supported by the Nature Science Foundation of Jiangxi
Province in China.
To a solution of compound 4 (1.0 mmol), aryl iodide
(1.1 mmol) and Pd(PPh3)4 (58 mg, 0.05 mmol) in DMF
(5 ml) was added CuI (19 mg, 0.1 mmol) under Ar. The
reaction mixture was stirred at room temperature for 48 h,
treated with saturated aqueous NH4Cl (10 ml) and ex-
tracted with CH2Cl2 (2 · 15 ml). The organic layer was
washed with saturated aqueous NH4Cl (2 · 10 ml),
water (3 · 20 ml) and dried (MgSO4). After removal of
the solvent, the residue was purified by column chroma-
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