Page 836 - Advanced Organic Chemistry Part B - Reactions & Synthesis

812 This method has been used to prepare alkenyl benzyldimethylsilanes. 76 These
derivatives are amenable to synthetic transformation involving F -mediated debenzy-
−
CHAPTER 9
lation.
Carbon-Carbon
Bond-Forming Reactions
2 8
3
2
of Compounds of Boron, CH O C(CH )
Silicon, and Tin
CH O C(CH ) C CH + PhCH 2 SiH(CH ) C CH 2
3 2
2
2 8
3
PhCH (CH ) Si
3 2
2
Other ruthenium-based catalysts are also active. Ruthenium dichloride–cymene
complex is stereoselective for formation of the Z-vinyl silanes from terminal alkynes.
RuCl (cymene) 2
2
(5 mol %) R SiPh 3
RC CH + Ph SiH
3
H H >95% Z
R = alkyl, aryl, alkoxyalkyl, acyloxyalkyl
Palladium-phosphine catalysts have also been used in the addition of triphenylsilane. 77
In this case, the E-silane is formed.
Pd (dba) 3 R H
2
0.5 mol %
RC CH + Ph SiH H
3
SiPh 3
High stereoselectivity was noted with Wilkinson’s catalyst in the reaction of
arylalkynes with diethoxymethylsilane. Interestingly, the stereoselectivity was
dependent on the order of mixing of the reagents and the catalyst. When the alkyne
was added to a mixture of catalyst and silane, the Z-isomer was formed. Reversing
the order and adding the silane to an alkyne-catalyst mixture led to formation of the
E-product. 78

RhCl(PPh )
3 3
(0.1 mol %) H Si(OC H ) CH
ArC CH + CH SiH(OC H ) 2 5 2 3
3
2 5 2
5 mol % NaI
Ar H
Tandem syn addition of alkyl and trimethylsilyl groups can be accomplished with
dialkylzinc and trimethylsilyl iodide in the presence of a Pd(0) catalyst. 79

R H
Pd(PPh )
3 4
RC CH +R′ Zn + (CH ) Sil C C
2
3 3
R′ Si(CH )
3 3
76 B. M. Trost, M. R. Machacek, and Z. T. Ball, Org. Lett., 5, 1895 (2003).
77
D. Motoda, H. Shinokubo, and K. Oshima, Synlett, 1529 (2002).
78 A. Mori, E. Takahisa, H. Kajiro, K. Hirabayashi, Y. Nishihara, and T. Hiyama, Chem. Lett., 443 (1998).
79
N. Chatani, N. Amishiro, T. Morii, T. Yamashita, and S. Murai, J. Org. Chem., 60, 1834 (1995).