Alternative synthesis of (Z)-1-aryl-1-(tributylstannyl)-2-(triethylgermyl)ethenes and the unprecedented germyl 1,2-migration during the destannylation of the adducts

Article abstract of DOI:10.1246/cl.2000.1408

A specific combination catalyst, Pd(dba)₂ and 4-ethyl-1-phospha-2,6,7-trioxabicyclo[2.2.2]octane, effectively catalyzed the addition of tributyl(triethylgermyl)stannane to aryl-acetylenes in tetrahydrofuran to give (Z)-1-aryl-2-(germyl)-1-(stannyl)ethenes in high yields. The (Z)-1-aryl-2-(germyl)-1-(stannyl)ethenes were subject to the unprecedented germyl 1,2-migration during the destannylation using HI / TBAI in toluene to produce 1-aryl-1-(germyl)ethenes in high yields.

Full text of DOI:10.1246/cl.2000.1408

1408
Chemistry Letters 2000
Alternative Synthesis of (Z)-1-Aryl-1-(tributylstannyl)-2-(triethylgermyl)ethenes and
the Unprecedented Germyl 1,2-Migration during the Destannylation of the Adducts
Taichi Nakano,* Yoshiya Senda, and Takashi Miyamoto
Department of Material Science and Technology, School of High-Technology for Human Welfare,
Tokai University, 317 Nishino, Numazu, Shizuoka 410-0395
(Received October 6, 2000; CL-000910)
A specific combination catalyst, Pd(dba)2 and 4-ethyl-1-
phospha-2,6,7-trioxabicyclo[2.2.2]octane, effectively catalyzed
the addition of tributyl(triethylgermyl)stannane to aryl-
acetylenes in tetrahydrofuran to give (Z)-1-aryl-2-(germyl)-1-
(stannyl)ethenes in high yields. The (Z)-1-aryl-2-(germyl)-1-
(stannyl)ethenes were subject to the unprecedented germyl 1,2-
migration during the destannylation using HI / TBAI in toluene
to produce 1-aryl-1-(germyl)ethenes in high yields.
Palladium-catalyzed silastannation of acetylenes has been
well studied and known to afford vicinal sila(stannyl)ethenes.1
The addition of a Ge–Sn bond of a (germyl)stannane to a triple
bond of nonterminal α,β-acetylenic esters catalyzed by
Pd(PPh3)4 forms a mixture of vicinal germa(stannyl)ethenes
with (E)- and (Z)-configrations.2 In contrast, the addition to ter-
minal alkynes involving phenylacetylene only forms the (Z)-
germyl(stannyl)ethenes, in which a germyl group is combined
with the terminal sp2 carbon.3 However, the yields did not
exceed 50%. We found that a specific combination catalyst,
Pd(dba)2 (dba = dibenzylideneacetone) and P(OCH2)3CEt (4-
ethyl-1-phospha-2,6,7-trioxabicyclo[2.2.2]octane, L), effective-
ly catalyzed the addition of tributyl(triethylgermyl)stannane 1
to arylacetylenes to produce (Z)-1-aryl-1-(tributylstannyl)-2-
(triethylgermyl)ethenes in high yields and the unprecedented
germyl 1,2-migration occurred during the destannylation of the
(Z)-1-aryl-2-(triethylgermyl)-1-(stannyl)ethenes to form 1-aryl-
1-(triethylgermyl)ethenes. We report these preliminary results.
The germastannation of phenylacetylene using 1 in THF
using the Pd(dba)2 and L4 combination catalyst afforded (Z)-1-
(tributylstannyl)-2-(triethylgermyl)-1-phenylethenes 2a5 in 85%
yield. The use of the THF solvent is essential in Scheme 1, in
contrast to no reaction in benzene.
Other reaction examples are summarized in Scheme 1 and
selected NMR data for 2a–e in Table 1.
Next, we examined the Kosugi·Migita-Stille coupling7 of
2a with allyl bromide in order to obtain chemical confirmation
for the structure. Thus, a DMF (N,N-dimethylformamide, 5
mL) solution of 2a (1 mmol), the bromide (5.5 mmol), Pd(dba)2
(0.01 mmol) and CuI (0.018 mmol) was stirred at 40 °C. The
reaction smoothly proceeded and went to completion in 5 h to
produce (E)-1-(triethylgermyl)-2-phenylpenta-1,4-diene 3a8 in
86% yield (Scheme 2). The reaction also proceeded at room
temperature to yield 3a in 85% yield, although a longer reaction
time (20 h) was needed.
The NMR spectrum of the 3a clearly showed that vinyl
proton on the sp2 carbon bearing the germyl group appeared as
a singlet (δ = 6.02 ppm), and supported the fact that the allyl
group did combine with the sp2 carbon bearing the phenyl
group, not another sp2 carbon. Results from Scheme 2 again
showed that 2a had the (Z)-configuration with the stannyl group
connected to the sp2-carbon bearing an aryl group. We next
examined a preliminary experiment for the destannylation of
2a, aimed at the synthesis of a series of trans-1-aryl-2-(triethyl-
germyl)ethenes using HI / TBAI (tetrabutylammonium iodide).
The method has been reported by Mori et al. as a selective sub-
The NMR coupling constants for 2a between tin and the
vinylic proton,3JSn-H, were –161.2 and –168.0 Hz for tin-117
and tin-119, respectively. These constants are typical for the
structure with tin and the vinylic proton in trans-disposition.3,6
Copyright © 2000 The Chemical Society of Japan

Chemistry Letters 2000
1409
stitution of the stannyl moiety in (Z)-1-(silyl)-2-(stannyl)alk-1-
(1986). d) B. L. Chenard, C. M. Van Zyl, and D. R.
Sanderson, Tetrahedron Lett., 27, 2801 (1986). e) T. N.
Mitchell, R. Wickenkamp, A. Amamria, R. Dicke, and U.
Schneider, J. Org. Chem., 52, 4868 (1987). f) K. Ritter,
Synthesis, 1989, 218. g) M. Mori, N. Watanabe, N. Kaneta,
and M. Shibasaki, Chem. Lett., 1991, 1651. h) M.
Murakami, H. Amii, N. Takizawa, and Y. Ito,
Organometallics, 12, 4223 (1993).
enes by hydrogen with retention of the configuration.1g
2
3
4
E. Piers and R. T. Skerlj, J. Chem. Soc., Chem. Commun.,
1987, 1025.
T. N. Mitchell, U. Schneider, and B. Fröhling, J.
Organomet. Chem., 384, C53 (1990).
P(OCH2)3CEt: For the use of the particular ligand in the
Pd-catalyzed addition of Si–Si and Ge–Ge bonds to
acetylenes in benzene solvent, see: (the former); H.
Yamashita, M. Catellani, and M. Tanaka, Chem. Lett.,
1991, 241. (the latter); a) T. Hayashi, H. Yamashita, T.
Sakakura, Y. Uchimaru, and M. Tanaka, Chem. Lett., 1991,
245. b) K. Mochida, C. Hodota, H. Yamashita, and M.
Tanaka, Chem. Lett., 1992, 1635.
However, strikingly enough, the destannylation of 2a did not
form the expected product, but only 1-(triethylgermyl)-1-phenyl-
ethene 4a9 {chemical shifts of vinyl protons; δ 5.89 ppm (d, 1H,
J = 2.4 Hz), 5.43 ppm (d, 1H, J = 2.4 Hz)} in an isolated yield
of 74%, as shown in Scheme 3. The reaction was very clean,
and no other products were formed except for tributylstannyl
iodide. Under similar reaction conditions, 2b also underwent a
migration to form 1-(p-chlorophenyl)-1-(triethylgermyl)ethene
4b10 in 80% yield. The 4a and 4b possibly form through the
Markownikov addition followed by the formation of a transient
cyclic cation, I-b, followed by destannylation forming a double
bond (the unprecedented germyl 1,2-migration), as shown in
Scheme 4.
5
A THF (5 mL) solution of 1 mmol, 4 mmol, 0.05 mmol
and 0.1 mmol of 1, phenylacetylene, Pd(dba)2 and L was
stirred at 80 °C for 50h. Treating the resulting mixture
with aqueous KF followed by purification by column chro-
matography (silica gel, hexane) gave spectroscopically
pure 2a in 85% yield. 1H-NMR (CDCl3) δ 7.24 (m, 2H),
7.13 (m, 2H), 6.98 (m, 1H), 6.63 (s, 1H), 1.4 (m, 6H), 1.26
(sep, 6H, J = 7.2 Hz), 1.07 (t, 9H, J = 7.6 Hz), 0.87 (m,
21H) ppm. Other reactions were carried out similar to the
synthesis of 2a. Reaction time; 19 h for 2b, 30 h for 2c, 40
h for 2d, and 35 h for 2e.
6
a) T. N. Mitchell, A. Amamria, H. Killing, and D.
Rutschow, J. Organomet. Chem., 241, C45 (1983). b) T. N.
Mitchell, A. Amamria, H. Killing, and D. Rutschow, J.
Organomet. Chem., 304, 257 (1986).
7
8
a) M. Kosugi, Y. Shimizu, and T. Migita, Chem. Lett.,
1977, 1423. b) D. Milstein and J. K. Stille, J. Am. Chem.
Soc., 100, 3636 (1978).
Treating the resulting mixture with aqueous KF followed
by purification by column chromatography (silica gel,
hexane) gave spectroscopically pure 3a in 86% yield. 1H-
NMR (CDCl3) δ 7.41 (m, 2H), 7.29 (m, 2H), 7.22 (m, 1H),
6.02 (s, 1H), 5.77 (m, 1H), 5.01 (m, 2H), 3.33 (m, 2H),
1.07 (t, 9H, J = 7.6 Hz), 0.91 (q, 6H, J = 7.6 Hz) ppm.
To a mixture of 2a (0.23 mmol), TBAI (0.23 mmol) and
toluene (1 mL) was added dropwise hydroiodic acid (0.35
mL, 57%) at 0 °C, then stirred for 1 h. The resulting mix-
ture was washed with aqueous sodium bicarbonate.
Treating the organic layer with aqueous KF followed by
purification by column chromatography (silica gel, hexane)
gave spectroscopically pure 4a in 74% yield. 1H NMR
(CDCl3) δ 7.28 (m, 2H), 7.19 (m, 3H), 5.89 (d, 1H, J = 2.4
Hz), 5.43 (d, 1H, J = 2.4 Hz), 1.01 (t, 9H, J = 7.6 Hz), 0.88
(q, 6H, J = 7.6 Hz) ppm.
Under similar conditions, (Z)-1-(tributylstannyl)-2-(tri-
methylsilyl)-1-phenylethene prepared by the palladium-cat-
alyzed addition of tributyl(trimethylsilyl)stannane to phenyl-
acetylene did not produce a similar type of silyl 1,2-migration.
The reaction gave 1-phenyl-2-(silyl)ethene. A full study for the
present reactions is now underway.
9
Financial support from the Shizuoka Shougou Kenkyu
Kikoh Foundation of Japan is gratefully acknowledged by one
of the authors (T. N.). The authors are indebted to Ms. Fumiyo
O-ikawa (Tokai University) for the mass measurements, espe-
cially the high resolution ones.
References and Notes
10 By a procedure similar to that for 4a, spectroscopically
1
1
a) T. N. Mitchell, H. Killing, R. Dicke, and R.
Wickenkamp, J. Chem. Soc., Chem. Commun., 1985, 354.
b) B. L. Chenard. E. D. Laganis, F. Davidson, and T. V.
RajanBabu, J. Org. Chem., 50, 3666 (1985). c) B. L.
Chenard and C. M. Van Zyl, J. Org. Chem., 51, 3561
pure 4b was isolated in 80% yield. H-NMR (CDCl3) δ
7.26 (dd, 2H, J = 6.4, 2.2 Hz), 7.09 (dd, 2H, J = 6.4, 2.2
Hz), 5.86 (d, 1H, J = 2.8 Hz), 5.43 (d, 1H, J = 2.8 Hz), 1.00
(t, 9H, J = 8.4 Hz), 0.87 (q, 6H, J = 8.4 Hz) ppm.