SILICON-PROMOTED CARBON-CARBON BOND FORMATION BETWEEN KETONES AND ALLYLSILANES OR VINYLSILANES CATALYZED BY MANGANESE(IV) DIOXIDE

The influence of silicon on the carbon-carbon bond formation was inves tigated by use of various silylalkenes to react with ketones. Treatmen t of an allylsilane (CH2=CHCH(2)SiMe(m)Ph(n); m + n 3) with various ke tones (20 equiv) in the presence of MnO2 (2.0 equiv) and a drop of ace tic acid at 140 degrees C in a sealed tube produced the corresponding hydrogen atom transfer adducts in 54-85% yields. Performance of the sa me reactions by replacement of the allylsilane with a vinylsilane (i.e ., CH2=CHSiMe(3) and CH2=CHSiMeEt(2)) afforded adducts in 59-75% yield s. Furthermore, reaction of diallyldimethylsilane with acetone or 3-me thyl-2-butanone under the same conditions afforded 4-(3,3-dimethyl-3-s ilacyclohexyl)butan-2-one (81%) and dimethyl-3-silacyclohexyl)-3,3-dim ethylbutan-2-one (65%), respectively. The results indicate that the al pha- and the beta-electronic effects of a silicon atom promoted the C- C bond formation, while the regioselectivity came from the steric effe ct of the silyl group.