Page 837 - Advanced Organic Chemistry Part B - Reactions & Synthesis

A possible mechanism involves formation of a Pd(II) intermediate that can undergo 813
cross coupling with the zinc reagent.
SECTION 9.2
R H PdL 4 Organosilicon
R′ SiMe 3 Me SiI Compounds
3
PdL 2
R′ Zn
2
R H Me Si Pd(L) 2 I
3
(L )Pd SiMe 3
2
I
R C CH

Several variations of the Peterson reaction have been developed for synthesis of
alkenylsilanes. 80 E- -Arylvinylsilanes can be obtained by dehydration of -silyloxy
alkoxides formed by addition of lithiomethyl trimethylsilane to aromatic aldehydes.
Specific Lewis acids have been found to be advantageous for the elimination step. 81

Cp TiCH AlCl(CH ) H Si(CH )
3 2
2.
2
ArCH O + LiCH Si(CH ) ArCHCH 2 Si(CH ) 3 3
3 3
3 3
2
Ar H
OLi
Alkenylsilanes can be prepared from aldehydes and ketones using
lithio(chloromethyl)trimethylsilane. The adducts are subjected to a reductive elimi-
nation by lithium naphthalenide. This procedure is stereoselective for the E-isomer
with both alkyl and aryl aldehydes. 82
+
Li naph – H Si(CH )
3 3
RCH O + LiCHSi(CH ) RCH CHSi(CH )
3 3
3 3
Cl s-BuLi O – Cl R H
TMEDA
ClCH Si(CH )
2
3 3
The adducts can be directed toward Z-alkenylsilanes by acetylation and reductive
elimination using SmI . 83
2
Ac O SmI 2 R Si(CH 3 ) 3
2
RCH CHSi(CH ) RCH CHSi(CH )
3 3
3 3
H H
O – Cl CH CO 2 Cl
3
The stereoselectivity in this case is attributed to elimination through a cyclic TS, but
is considerably reduced with aryl aldehydes.
CH 3 O SmI 2
O
R
)
Si(CH 3 3
80 C. Trindle, J.-T. Hwang, and F. A. Carey, J. Org. Chem., 38, 2664 (1973); P. F. Hudrlik,
E. L. Agwaramgbo, and A. M. Hudrlik, J. Org. Chem., 54, 5613 (1989).
81
M. L. Kwan, C. W. Yeung, K. L. Breno, and K. M. Doxsee, Tetrahedron Lett., 42, 1411 (2001).
82 J. Barluenga, J. L. Fernandez-Simon, J. M. Concellon, and M. Yus, Synthesis, 234 (1988).
83
J. M. Concellon, P. L. Bernad, and E. Bardales, Org. Lett., 3, 937 (2001).