Page 587 - Advanced Organic Chemistry Part A - Structure and Mechanisms, 5th ed (2007) - Carey _ Sundberg

568 HOMO and enhances reactivity. 316 MP3/6-31G* calculations indicate a stabilization of
38 kcal/mol, which is about the same as the value calculated for an -methyl group. 317
CHAPTER 5
Furthermore, this stereoelectronic interaction favors attack of the electrophile anti to
Polar Addition the silyl substituent. The reaction is then completed by the elimination step in which
and Elimination
Reactions the carbon-silicon or carbon-tin bond is broken.
Allyl silanes and allyl stannanes are also reactive toward electrophiles and usually
undergo a concerted elimination of the silyl substituent.

) SiCH CH CH + I CH CHCH I
(CH 3 3 2 2 2 2 2
Ref. 318

C(CH )
3 3
TiCl 4
(CH ) SiCH CH CH(CH ) CH 3 + (CH ) CCl CH 2 CHCH(CH ) CH 3
3 3
2 5
2 5
3 3
2
Ref. 319
CH
(CH ) SnCH 2 2
3 3
+ BrCH CH C(CH ) (CH ) CH C(CH )
CH 2 2 3 2 CH CH 2 2 3 2
CH 2 CH 2
Ref. 320

(Et) AlSO 4
2
(CH ) SnCH CH CH 2 + (CH O) CHCH CH Ph CH 2 CHCH CHCH CH Ph
2
3
2
2
2
2
2
2
3 3
OCH 3
Ref. 321
The common mechanistic pattern in these reactions involves electron release toward
the developing electron deficiency on the C(2) of the double bond. Completion of the
reaction involves loss of the electron-donating group and formation of the double bond.
Further examples of these synthetically useful reactions can be found in Section 9.3
in Part B.
E +
RCH CH CH 2 RCH CHCH E
2
M

316
S. D. Kahn, C. F. Pau, A. R. Chamberlin, and W. J. Hehre, J. Am. Chem. Soc., 109, 650 (1987).
317 S. E. Wierschke, J. Chandrasekhar, and W. L. Jorgensen, J. Am. Chem. Soc., 107, 1496 (1985).
318 D. Grafstein, J. Am. Chem. Soc., 77, 6650 (1955).
319
I. Fleming and I. Paterson, Synthesis, 445 (1979).
320 J. P. Godschalx and J. K. Stille, Tetrahedron Lett., 24, 1905 (1983).
321
A. Hosomi, H. Iguchi, M. Endo, and H. Sakurai, Chem. Lett., 977 (1979).