Abstract
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 (CH 2 =CHCH 2 SiMe m Ph n ; m + n = 3) with various ketones (20 equiv) in the presence of MnO 2 (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., CH 2 =CHSiMe 3 and CH 2 =CHSiMeEt 2 ) 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 α- and the β-electronic effects of a silicon atom promoted the C-C bond formation, while the regioselectivity came from the steric effect of the silyl group. © 1995 American Chemical Society.