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The influence of silicon on the carbon-carbon bond formation was investigated by use of various silylalkenes to react with ketones. Treatment of an allylsilane (CH2=CHCH2SiMen,Ph"; m + n = 3) with various ketones (20 equiv) in the presence of Mn02 (2.0 equiv) and a drop of acetic acid at 140 °C in a sealed tube produced the corresponding hydrogen atom transfer adducts in 54-85% yields. Performance of the same reactions by replacement of the allylsilane with a vinylsilane (i.e., CH2=CHSiMe3 and CH2=CHSiMeEt2) afforded adducts in 59-75% yields. Furthermore, reaction of diallyldimethylsilane with acetone or 3-methyl-2-butanone under the same conditions afforded 4-(3,3-dimethyl-3-silacyclohexyl)butan-2-one (81%) and 4-(3,3-dimethyl-3-silacyclohexyl)-3,3-dimethylbutan-2-one (65%), respectively. The results indicate that the a-and the /^-electronic effects of a silicon atom promoted the C-C bond formation, while the regioselectivity came from the steric effect of the silyl group.* Recipient of the Federation of Asian Chemical Societies 1992 and 1993 Distinguished Young Chemist Award.* Academia Sinica.

Electron-impact-induced fragmentations were performed in the gas phase on δ-silyl aldehydes, ketones, thioketones, carboxylic acids, and acetates. All of these compounds showed significant silyl migration through a transition state with a seven-membered ring. For ketones and acetates, this silyl migration process may overwhelm the McLafferty rearrangement, which involves a transition state with a six-membered ring.