Stereoselective synthesis of (Z)-1-Silyl-2-stannylethene by palladium-catalyzed silastannation of ethyne and its synthetic transformations

Article abstract of DOI:10.1055/s-2004-822405

(Z)-1-Silyl-2-stannylethenes were stereoselectively synthesized by silastannation of ethyne, catalyzed by a palladium/tert-alkyl isocyanide catalyst, and the synthetic utilities were demonstrated by their transformations.

Full text of DOI:10.1055/s-2004-822405

1522
PAPER
Stereoselective Synthesis of (Z)-1-Silyl-2-stannylethene by Palladium-
Catalyzed Silastannation of Ethyne and Its Synthetic Transformations
H
ighly Stereoselective
a
Silastanna
t
s
ion of Eth
a
yne hiro Murakami,* Takanori Matsuda, Kenichiro Itami, Shinji Ashida, Miki Terayama
Department of Synthetic Chemistry and Biological Chemistry, Kyoto University, Katsura, Kyoto 615-8510, Japan
Fax +81(75)3832748; E-mail: murakami@sbchem.kyoto-u.ac.jp
Received 16 April 2004
Dedicated to Professor Teruaki Mukaiyama on the occasion of his 77th birthday with admiration for his outstanding contribution to organic
synthesis.
of palladium(II) acetate (2 mol%) and 1,1,3,3-tetrameth-
Abstract: (Z)-1-Silyl-2-stannylethenes were stereoselectively syn-
ylbutyl isocyanide (8 mol%) in toluene at 35 °C,8 the ad-
dition reaction proceeded to completion (Scheme 1). H
thesized by silastannation of ethyne, catalyzed by a palladium/tert-
alkyl isocyanide catalyst, and the synthetic utilities were demon-
1
NMR analysis of the crude reaction mixture revealed that
(Z)-1-tributylstannyl-2-(trimethylsilyl)ethene (2a) was
formed as the major product together with a small amount
of bis-stannation product (<5%).9 The pure silastannation
product was obtained in 86% yield (Z/E = 96/4) by simple
bulb-to-bulb distillation. The stereochemistry of the sila-
stannation product 2a was unambiguously confirmed by
the coupling constant (J = 18.4 Hz for Z; 23.0 Hz for E) of
the two vicinal vinylic protons in the 1H NMR spectrum.
Dimethylphenylsilyl derivative 1b similarly underwent
the reaction with ethyne to give rise to the Z adduct 2b.10
strated by their transformations.
Key words: palladium, alkyne, silylstannane, cis-addition, cross-
coupling
Because of the widespread use of organosilicon and -tin
compounds in organic synthesis,1 it is evermore desired to
establish efficient and practical methods to prepare these
organometallic compounds in a regio- and stereodefined
form. Compounds having both carbon–silicon and car-
bon–tin bonds in the molecule would allow stepwise
transformations of the two carbon–metal bonds based on
the difference in their intrinsic reactivities. For instance,
1-silyl-2-stannylethene is a highly useful synthetic inter-
mediate for building olefinic compounds. (E)-1-Silyl-2-
stannylethene can be easily prepared by hydrostannation
of ethynylsilane2 and has been used as a valuable building
block.3 On the other hand, the corresponding Z isomer re-
ceived much less attention. Whereas the Z isomer can be
prepared by stannylcupration of ethyne (HC≡CH),4 cis-
silastannation5,6 of ethyne would provide a more straight-
forward approach to the Z isomer. However, silastanna-
tion of ethyne using Pd(PPh3)4 at 55 °C was reported to
afford a mixture of Z and E isomers with the latter pre-
dominating (1:4).5c It is likely that the Z isomer initially
formed isomerized to the E isomer, which was thermody-
namically more stable.
Scheme 1
Next, the silastannated products were used for further syn-
thetic transformations to demonstrate their utilities as a
building block. Lithiation of the vinylstannane moiety of
2a with n-BuLi followed by the reaction with aldehydes
gave g-trimethylsilyl allylic alcohols 3 with retention of
the Z stereochemistry (Scheme 2). Then, (Z)-g-trimethyl-
silyl allylic alcohols 3 were subjected to the copper(I)-
promoted cross-coupling reaction, developed recently by
Takeda et al.11 The cross-coupling of 3 with allyl and ben-
zyl halides successfully took place to afford only (Z)-al-
lylic alcohols 4. The minor E isomer remained unchanged
because the cross-coupling reaction involved intramolec-
ular 1,4-silyl migration from the sp2 carbon to oxygen.
We have reported that a palladium/tert-alkyl isocyanide
catalyst is so active that the silastannation of mono-substi-
tuted alkynes proceeded at room temperature to give 2-
substituted (Z)-1-silyl-2-stannylethenes.6 Now, we report
the stereoselective synthesis of (Z)-1-silyl-2-stan-
nylethene with the use of the palladium/tert-alkyl isocya-
nide complex7 as the catalyst for the silastannation of
ethyne. The synthetic transformations were also exam-
ined.
Both vinylsilanes and -stannanes are known to react with
an iodonium source to produce vinyl iodides. However,
treatment of 2a with iodine (1.15 equiv) gave (Z)-1-iodo-
2-(trimethylsilyl)ethene (5) in 42% isolated yield via
chemoselective and stereospecific replacement of the
stannyl group with an iodo group (Scheme 3). It is of note
that the stereoselective synthesis of the iodide 5 was un-
precedented.12
When tributyl(trimethylsilyl)stannane (1a) was stirred for
one day under a balloon pressure of ethyne in the presence
SYNTHESIS 2004, No. 9, pp 1522–1526
Advanced online publication: 08.06.2004
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DOI: 10.1055/s-2004-822405; Art ID: C04104SS
© Georg Thieme Verlag Stuttgart · New York

PAPER
Highly Stereoselective Silastannation of Ethyne
1523
Scheme 2
Scheme 3
Various synthetic transformations, like a cross-coupling
reaction, can be carried out much easier with an isopro-
poxydimethylsilyl group than with trimethylsilyl and
dimethylphenylsilyl groups. On the other hand, an isopro-
poxydimethylsilyl group is adequately stable against hy-
drolysis. Thus, we next examined the silastannation using
silylstannanes having an isopropoxy group on the silicon
(1c and 1d). Silylstannanes 1c and 1d were prepared from
the corresponding aminochlorosilanes13 as shown in
Scheme 4. The silastannation reaction of 1c and 1d also
took place under the same conditions. In addition, a com-
plete cis-stereoselectivity was observed in the products
(2c and 2d).
Scheme 5
was demonstrated by their synthetic transformations. The
Z olefinic geometries were kept during the transforma-
tions shown in Schemes 2, 3, and 5. Thus, the (Z)-1-silyl-
2-stannylethenes offer a versatile synthetic platform for
the cis-disubstituted -CH=CH- skeleton.
Unless otherwise noted, all chemicals and anhydrous solvents were
obtained from commercial suppliers and used as received. All reac-
tions were carried out under a nitrogen atmosphere. Column chro-
matography was performed with silica gel 60 N (Kanto).
Preparative thin-layer chromatography was performed with silica
gel 60 PF254 (Merck). 1H and 13C NMR spectra were recorded on a
Varian Gemini 2000 (1H at 300.07 MHz and 13C at 75.46 MHz)
spectrometer or a Varian Mercury 400 (1H at 400.44 MHz). Proton
chemical shifts are referenced to residual CHCl3. Carbon chemical
shifts are referenced to CDCl3. 29Si and 119Sn NMR spectra were re-
corded on a JEOL JNM-A400 spectrometer (29Si at 79.30 MHz and
119Sn at 148.95 MHz). Silicon and tin chemical shifts are referenced
to external standards Me4Si and Me4Sn, respectively. High resolu-
tion mass spectra were recorded on a JEOL JMS-SX102A spec-
trometer. Chloro(diethylamino)dimethylsilane was prepared
according to the literature method.
Scheme 4
The silastannated product 2c, having an isopropoxydi-
methylsilyl group, has a broader scope as a building
block. For example, the successive cross-coupling of 2c
can be carried out in one-pot reaction. In the presence of a
palladium/copper catalyst,14 2c was treated with ethyl p-
iodobenzoate to give (Z)-b-silylstyrene derivative 6. Ad-
dition of p-iodoanisole and tetrabutylammonium fluoride
(TBAF) to the reaction mixture afforded the stilbene de-
Preparation of Silylstannanes
Isopropoxy(dimethyl)(tributylstannyl)silane (1c)
To a THF solution (150 mL) of Bu3SnLi, which was prepared from
Bu3SnH (43.7 g, 150 mmol) and LDA, was added (Et2N)Me2SiCl
(26.1 g, 158 mmol) dropwise at 0 °C, and the reaction mixture was
allowed to warm to r.t. overnight. The reaction mixture was diluted
with hexane, filtered through Celite®, and concentrated. Further fil-
rivative 7 without loss of the Z stereochemistry tration through Celite® (hexane-Et2O, 3:1) followed by distillation
(Scheme 5).15 Likewise, the coupling of 6 with 2-thienyl
iodide took place in a similar manner to give 8.
(138 °C/0.9 mmHg) gave Bu3Sn–SiMe2(NEt2) (52.6 g, 83%) as a
pale yellow oil. A mixture of Bu3Sn–SiMe2(NEt2) (25.2 g, 60
mmol) and NH4Cl (1.5 g) in i-PrOH (120 mL) was stirred at r.t.
In summary, highly stereoselective cis-silastannation of
overnight. The reaction mixture was diluted with hexane, filtered
ethyne catalyzed by a palladium/tert-alkyl isocyanide through Celite®, and concentrated. Further filtration through Celite®
(hexane-Et2O, 3:1) followed by distillation (120 °C/0.4 mmHg)
gave 1c (19.8 g, 81%) as a pale yellow oil.
complex was achieved, and the usefulness of the products
Synthesis 2004, No. 9, 1522–1526 © Thieme Stuttgart · New York

1524
M. Murakami et al.
PAPER
Isopropoxy(dimethyl)[(Z)-2-(tributylstannyl)vinyl]silane (2c)
A mixture of Pd(OAc)2 (27 mg, 0.12 mmol), 1,1,3,3-tetramethylbu-
tyl isocyanide (65 mg, 0.46 mmol), and silylstannane 1b (2.23 g,
5.48 mmol) in toluene (48 mL) was stirred under a balloon pressure
of ethyne for 2 h at 35 °C in the dark. The reaction mixture was
passed through a plug of Florisil® (Et2O), and the volatile materials
were evaporated. Bulb-to-bulb distillation (140 °C/0.3 mmHg) af-
forded 2c (1.94 g, 81%) as a yellow oil.
1H NMR (300 MHz): d = 0.37 (s, 3JSn–H = 19.5 Hz, 6 H), 0.77-0.95
(m, 15 H), 1.16 (d, J = 6.1 Hz, 6 H), 1.24-1.38 (m, 6 H), 1.42-1.57
(m, 6 H), 3.90 (sept, J = 6.1 Hz, 1 H).
13C NMR: d = 4.5 (2JSn–C = 83.5 Hz), 8.2 (1JSn–C = 252.9, 241.5 Hz),
13.7, 25.7, 27.6 (2JSn–C = 51.0 Hz), 30.3 (3JSn–C = 17.4 Hz), 66.8.
29Si NMR (CDCl3): d = 21.6.
119Sn NMR (CDCl3): d = –141.1.
HRMS (EI): m/z calcd for C17H40OSiSn (M+), 408.1870; found,
408.1872.
1H NMR (300 MHz): d = 0.18 (s, 6 H), 0.77-1.06 (m, 15 H), 1.17
(d, J = 6.3 Hz, 6 H), 1.24-1.37 (m, 6 H), 1.44-1.56 (m, 6 H), 4.02
3
(sept, J = 6.3 Hz, 1 H), 6.91 (d, J = 18.9 Hz, JSn–H = 179.3, 171.0
Anal. Calcd for C17H40OSiSn: C, 50.13; H, 9.90. Found: C, 50.37;
H, 9.63.
Hz, 1 H), 7.18 (d, J = 18.9 Hz, 2JSn–H = 84.5, 80.6 Hz, 1 H).
13C NMR: d = –0.2, 11.1, 13.8, 25.8, 27.4, 29.2, 65.1, 150.9, 153.3.
HRMS (EI): m/z calcd for C15H33OSiSn (M+ – Bu), 377.1323;
found, 377.1322.
Diethyl(isopropoxy)(tributylstannyl)silane (1d)
According to the procedure analogous to that described for 1c, 1d
was prepared as a pale yellow oil.
1H NMR (300 MHz): d = 0.75-0.93 (m, 19 H), 0.95-1.13 (m, 6 H),
1.16 (d, J = 6.0 Hz, 6 H), 1.25-1.38 (m, 6 H), 1.42-1.55 (m, 6 H),
3.89 (sept, J = 6.0 Hz, 1 H).
Diethyl(isopropoxy)[(Z)-2-(tributylstannyl)vinyl]silane (2d)
According to the procedure analogous to that described for 2c, 2d
(2.09 g, 89%) was prepared from 1d (2.21 g, 5.07 mmol).
1H NMR (400 MHz): d = 0.61-0.69 (m, 4 H), 0.86-1.10 (m, 21 H),
1.18 (d, J = 6.0 Hz, 6 H), 1.26-1.36 (m, 6 H), 1.46-1.54 (m, 6 H),
13C NMR: d = 7.3, 8.6 (1JSn–C = 248.2, 236.6 Hz),
10.4
(2JSn–C = 77.7 Hz), 13.7, 25.7, 27.7 (2JSn–C = 52.2 Hz), 30.3
3
(3JSn–C = 17.4 Hz), 67.1.
HRMS (EI): m/z calcd for C15H35OSiSn (M+ – Bu), 379.1479;
4.03 (sept, J = 6.0 Hz, 1 H), 6.83 (d, J = 18.8 Hz, JSn–H = 181.0,
173.0 Hz, 1 H), 7.24 (d, J = 18.8 Hz, 2JSn–H = 84.8, 81.6 Hz, 1 H)
13C NMR: d = 6.2, 7.1, 11.1, 13.8, 25.8, 27.5, 29.2, 65.1, 148.3,
154.4.
HRMS (EI): m/z calcd for C17H37OSiSn (M+ – Bu), 405.1636;
found, 405.1644.
found, 379.1478.
Anal. Calcd for C19H44OSiSn: C, 52.42; H, 10.19. Found: C, 52.69;
H, 10.45.
Silastannation of Ethyne
Trimethyl[(Z)-2-(tributylstannyl)vinyl]silane (2a)
Synthesis of (Z)-Allylic Alcohols 3
(Z)-1-Phenyl-3-(trimethylsilyl)prop-2-en-1-ol (3a)
To a flask containing Pd(OAc)2 (4.5 mg, 0.020 mmol) and 1,1,3,3-
tetramethylbutyl isocyanide (11 mg, 0.080 mmol) were added suc-
cessively toluene (10 mL) and silylstannane 1a (362 mg, 1.00
mmol) at r. t. A balloon filled with gaseous ethyne was then attached
to the flask via a three-way joint. The flask was then evacuated and
refilled with ethyne from the balloon four times and the mixture was
stirred for 1 day at 35 °C in the dark. The volatile materials were re-
moved under reduced pressure, and the residue was filtered through
a plug of Florisil® (hexane) and concentrated. The residue was sub-
jected to bulb-to-bulb distillation (97–99 °C/1 mmHg) to afford 2a
(332 mg, 86%) as a pale yellow oil.
1H NMR (300 MHz): d = 0.10 (s, 9 H), 0.84–0.97 (m, 15 H), 1.23–
1.39 (m, 6 H), 1.43–1.57 (m, 6 H), 7.00 (d, J = 18.6 Hz, 1 H), 7.12
(d, J = 18.6 Hz, 1 H).
13C NMR: d = –0.5, 11.1 (1JSn–C = 334.0, 320.1 Hz), 13.7, 27.4
(2JSn–C = 56.8 Hz), 29.2 (3JSn–C = 19.7 Hz), 151.0, 153.7
(2JSn–C = 29.1 Hz).
To a solution of 2a (1.97 g, 5.1 mmol) in THF (25 mL) was added
n-BuLi (1.56 M in hexane, 3.9 mL, 6.1 mmol) at –78 °C, and the re-
action mixture was stirred for 2 h at –78 °C. Benzaldehyde (806 mg,
7.6 mmol) was added, and then the mixture was gradually warmed
to r.t. After evaporating the solvents, the residue was extracted with
Et2O (3 ×), and the organic layer was washed with brine, dried over
Na2SO4, and concentrated. The residue was purified by column
chromatography on silica gel (hexane-EtOAc, 6:1) to give 3a (763
mg, 73%, Z/E = 95/5).
1H NMR (300 MHz): d = 0.20 (s, 9 H), 1.87 (br s, 1 H), 5.33 (d,
J = 9.0 Hz, 1 H), 5.75 (dd, J = 13.9, 0.6 Hz, 1 H), 6.41 (dd, J = 13.9,
9.0 Hz, 1 H), 7.23-7.42 (m, 5 H).
13C NMR: d = 0.6, 74.1, 126.0, 127.6, 128.5, 132.2, 142.7, 148.5.
29Si NMR (CDCl3): d = –9.8.
HRMS (EI): m/z calcd for C12H18OSi (M+), 206.1127; found,
206.1130.
HRMS (EI): m/z calcd for C13H29SiSn (M+ – Bu), 333.1061; found,
333.1065.
For the E isomer:
1H NMR (300 MHz): d = 0.07 (s, 9 H), 5.17 (d, J = 5.3 Hz, 1 H),
5.99 (dd, J = 18.7, 1.1 Hz, 1 H), 6.19 (dd, J = 18.7, 5.3 Hz, 1 H),
7.23-7.42 (m, 5 H).
Dimethyl(phenyl)[(Z)-2-(tributylstannyl)vinyl]silane (2b)
According to the procedure analogous to that described for 2a, 2b
(396 mg, 90%) was prepared from 1b (415 mg, 0.98 mmol).
(Z)-5-Phenyl-1-(trimethylsilyl)pent-1-en-3-ol (3b)
According to the procedure described for 3a, 3b (991 mg, 85%, Z/
E = 97/3) was prepared from 2a (1.94 g, 4.97 mmol) and 3-phenyl-
propanal (1.00 g, 7.45 mmol).
1H NMR (300 MHz): d = 0.05 (s, 9 H), 1.49 (br s, 1 H), 1.66-1.97
(m, 2 H), 2.60-2.80 (m, 2 H), 4.22 (dt, J = 5.2, 8.5 Hz, 1 H), 5.66
(d, J = 14.1, 0.8 Hz, 1 H), 6.27 (dd, J = 14.1, 8.5 Hz, 1 H), 7.13-
7.31 (m, 5 H).
1H NMR (300 MHz): d = 0.36 (s, 6 H), 0.77-0.94 (m, 15 H), 1.20-
1.33 (m, 6 H), 1.38-1.54 (m, 6 H), 7.16 (d, J = 18.9 Hz, 1 H), 7.29
(d, J = 18.9 Hz, 1 H), 7.31-7.38 (m, 3 H), 7.51-7.57 (m, 2 H).
13C NMR: d = –1.5, 11.0 (1JSn–C = 335.2, 321.3 Hz), 13.7, 27.3
(2JSn–C = 56.9 Hz), 29.1 (3JSn–C = 19.7 Hz), 127.7, 128.9, 134.0,
139.1, 151.2, 153.8.
29Si NMR (CDCl3): d = –13.7.
119Sn NMR (CDCl3): d = –68.0.
HRMS (EI): m/z calcd for C18H31SiSn (M+ – Bu), 395.1217; found,
13C NMR: d = 0.3, 31.7, 38.7, 71.6, 125.8, 128.35, 128.43, 132.1,
141.7, 149.7.
395.1220.
Synthesis 2004, No. 9, 1522–1526 © Thieme Stuttgart · New York

PAPER
Highly Stereoselective Silastannation of Ethyne
1525
HRMS (EI): m/z calcd for C14H22OSi (M+), 234.1440; found,
234.1439.
chromatography on silica gel (hexane-EtOAc, 10:1) to afford 7
(166 mg, 65%).
1H NMR (300 MHz): d = 1.39 (t, J = 7.1 Hz, 3 H), 3.79 (s, 3 H),
4.37 (q, J = 7.1 Hz, 2 H), 6.51 (d, J = 12.3 Hz, 1 H), 6.63 (d,
J = 12.3 Hz, 1 H), 6.73-6.79 (m, 2 H), 7.13-7.20 (m, 2 H), 7.31-
7.36 (m, 2 H), 7.89-7.95 (m, 2 H).
13C NMR: d = 14.3, 55.1, 60.8, 113.6, 127.6, 128.7, 129.0, 129.4,
130.1, 131.6, 142.3, 158.9, 166.3 [one carbon signal is missing due
to overlapping].
Copper-Promoted Cross-Coupling of 3
(Z)-1-Phenylhexa-2,5-dien-1-ol (4a)
To a DMF suspension (9 mL) of CuI (524 mg, 2.75 mmol) was add-
ed t-BuOLi (240 mg, 3.00 mmol) at 0 °C. After the mixture was
stirred for 20 min at r.t., a DMF solution (8 mL) of 3a (514 mg, 2.49
mmol) and a DMF solution (8 mL) of allyl chloride (230 mg, 3.01
mmol) were successively added to the mixture. After being stirred
for 2 h at r.t., the reaction mixture was quenched by addition of an
aq NH3 solution (3.5%). The organic materials were extracted with
Et2O, dried over Na2SO4, and concentrated. The residue was dis-
solved in THF (25 mL), and TBAF (1.0 M in THF, 2.5 mL, 2.5
mmol) was added to the solution. The mixture was stirred at r.t. and
diluted with H2O. The organic materials were extracted with
EtOAc, washed with 1 M HCl and then with H2O, dried over
Na2SO4, and concentrated. The residue was purified by column
chromatography on silica gel (hexane-EtOAc, 6:1) to afford 4a
(290 mg, 67%).
1H NMR (300 MHz): d = 1.90 (s, 1 H), 2.87-3.07 (m, 2 H), 5.02
(dq, J = 9.8, 1.6 Hz, 1 H), 5.07 (dq, J = 17.0, 1.7 Hz, 1 H), 5.49-
5.65 (m, 2 H), 5.66-5.71 (m, 1 H), 5.83 (ddt, J = 17.1, 10.2, 6.4 Hz,
1 H), 7.22-7.41 (m, 5 H).
13C NMR: d = 31.9, 69.7, 115.5, 125.9, 127.5, 128.5, 129.0, 133.0,
136.0, 143.4.
HRMS (EI): m/z calcd for C18H18O3, 282.1256; found, 282.1255.
Ethyl 4-[(Z)-2-(2-Thienyl)vinyl]benzoate (8)
According to the procedure analogous to that described for 7, 8 (157
mg, 61%) was prepared from 2c (433 mg, 1.00 mmol), ethyl 4-io-
dobenzoate (248 mg, 0.90 mmol), and 2-thienyl iodide (189 mg,
0.90 mmol).
1H NMR (300 MHz): d = 1.4 (t, J = 7.1 Hz, 3 H), 4.39 (q, J = 7.1
Hz, 2 H), 6.56 (d, J = 12.2 Hz, 1 H), 6.76 (d, J = 12.2 Hz, 1 H), 6.89
(dd, J = 5.0, 3.5 Hz, 1 H), 6.97 (d, J = 3.5 Hz, 1 H), 7.12 (dd,
J = 5.0, 1.2 Hz, 1 H), 7.44 (d, J = 8.0 Hz, 2 H), 8.03 (dt, J = 8.0, 1.8
Hz, 2 H).
13C NMR: d = 14.3, 60.9, 124.4, 125.8, 126.5, 127.7, 128.5, 128.7,
129.4, 129.7, 139.1, 142.0, 166.3.
HRMS (EI): m/z calcd for C15H14O2S, 258.0715; found, 258.0721.
HRMS (EI): m/z calcd for C12H14O (M+), 174.1045; found,
174.1051.
References
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J. Chem. Soc., Chem. Commun. 1985, 354. (b) Chenard, B.
L.; Laganis, E. D.; Davidson, F.; RajanBabu, T. V. J. Org.
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(Z)-1,6-Diphenylhex-4-en-3-ol (4b)
According to the procedure analogous to that described for 4a, 4b
(387 mg, 60%) was prepared from 3b (596 mg, 2.54 mmol) and
benzyl bromide (856 mg, 5.00 mmol).
1H NMR (300 MHz): d = 1.59 (s, 1 H), 1.82 (dddd, J = 13.6, 9.5,
6.8, 5.9 Hz, 1 H), 1.91-2.06 (m, 1 H), 2.64-2.82 (m, 2 H), 3.38 (dd,
J = 15.5, 7.5 Hz, 1 H), 3.46 (dd, J = 15.5, 7.5 Hz, 1 H), 4.59 (dt,
J = 6.6, 7.5 Hz, 1 H), 5.58 (ddt, J = 10.8, 8.7, 1.5 Hz, 1 H), 5.73 (ddt,
J = 10.8, 0.9, 7.5 Hz, 1 H), 7.14-7.25 (m, 6 H), 7.26-7.34 (m, 4 H).
13C NMR: d = 31.7, 33.9, 39.0, 67.0, 125.8, 126.1, 128.2, 128.4
[overlapping], 128.5, 130.6, 133.1.
HRMS (EI): m/z calcd for C18H18 (M+ – H2O), 234.1409; found,
234.1406.
Iododestannation of 2a
[(Z)-2-Iodovinyl](trimethyl)silane (5)12
To a solution of 2a (778 mg, 2.00 mmol) in Et2O (6 mL) was added
a solution of I2 (583 mg, 2.30 mmol) in Et2O (6 mL) dropwise at
0 °C. After the mixture was stirred for 1 h at 0 °C, 0.5 M aq solution
of Na2S2O3 and sat. aq solution of KF were successively added to
the reaction mixture. The organic materials were extracted with
Et2O, and the solvent was evaporated (200 mmHg). The residue was
subjected to bulb-to-bulb distillation (90 °C/20 mmHg) to afford 5
(193 mg, 42%).
Palladium-Catalyzed Successive Cross-Coupling of 2c
Ethyl 4-[(Z)-2-(4-Methoxyphenyl)vinyl]benzoate (7)
Wickenkamp, R.; Amamria, A.; Dicke, R.; Schneider, U. J.
Org. Chem. 1987, 52, 4868. (e) Ritter, K. Synthesis 1989,
218. (f) Casson, S.; Kocienski, P. J.; Reid, G.; Smith, N.;
Street, J. M.; Webster, M. Synthesis 1994, 1301. (g) Lunot,
S.; Thibonnet, J.; Duchêne, A.; Parrain, J.-L.; Abarbri, M.
Tetrahedron Lett. 2000, 41, 8893. (h) Minière, S.; Cintrat,
J.-C. Synthesis 2001, 705. (i) Hemeon, I.; Singer, R. D.
Chem. Commun. 2002, 1884. (j) Naud, S.; Cintrat, J.-C.
Synthesis 2003, 1391.
A mixture of 2c (433 mg, 1.00 mmol), ethyl 4-iodobenzoate (248
mg, 0.90 mmol), PhCH2PdCl(PPh3)2 (36 mg, 0.048 mmol), and CuI
(19 mg, 0.10 mmol) in DMF (3 mL) was stirred for 30 min at r.t.,
and then for 3 h at 50 °C. 4-Iodoanisole (210 mg, 0.90 mmol) and
TBAF (1.0 M in THF, 2.5 mL, 2.5 mmol) were added to the reaction
mixture at 0 °C. After the mixture was stirred for 8 h at 50 °C, sat.
aq solution of KF was added to the mixture. The organic materials
were extracted with EtOAc, passed through a plug of Florisil®
(EtOAc), and concentrated. The residue was purified by column
(6) Murakami, M.; Amii, H.; Takizawa, N.; Ito, Y.
Organometallics 1993, 12, 4223.
Synthesis 2004, No. 9, 1522–1526 © Thieme Stuttgart · New York

1526
M. Murakami et al.
PAPER
(7) The palladium/isocyanide complex is also effective for
activation of silicon–silicon and silicon–boron bonds, see:
(a) Ito, Y.; Suginome, M.; Murakami, M. J. Org. Chem.
1991, 56, 1948. (b) Suginome, M.; Matsuda, T.; Nakamura,
H.; Ito, Y. Tetrahedron 1999, 55, 8787.
(10) Interestingly, the reaction with trimethyl(dimethylphenyl-
silyl)stannane in place of 1b gave no silastannation product
at all. Instead, 1,2-diphenyltetramethyldisilane was formed
by disproportionation.
(11) (a) Taguchi, H.; Ghoroku, K.; Tadaki, M.; Tsubouchi, A.;
Takeda, T. J. Org. Chem. 2002, 67, 8450. (b) Taguchi, H.;
Tsubouchi, A.; Takeda, T. Tetrahedron Lett. 2003, 44, 5205.
(12) Pillot, J.-P.; Dunoguès, J.; Calas, R. Synth. Commun. 1979,
9, 395.
(13) Tamao, K.; Nakajo, E.; Ito, Y. Tetrahedron 1988, 44, 3997.
(14) Liebeskind, L. S.; Fengl, R. W. J. Org. Chem. 1990, 55,
5359.
(15) Tamao, K.; Kobayashi, K.; Ito, Y. Tetrahedron Lett. 1989,
30, 6051.
(8) The reaction failed to proceed effectively at room
temperature.
(9) It was formed via disproportionation of silylstannane to
distannane followed by bis-stannation of ethyne. For bis-
stannation of ethyne see: (a) Mitchell, T. N.; Killing, A. A.
H.; Rutschow, D. J. Organomet. Chem. 1983, 241, C45.
(b) Mitchell, T. N.; Killing, A. A. H.; Rutschow, D. J.
Organomet. Chem. 1986, 304, 257.
Synthesis 2004, No. 9, 1522–1526 © Thieme Stuttgart · New York