Lewis acid-catalyzed regio- and stereoselective hydrosilylation of alkenes with trialkylsilanes

The hydrosilylation of cyclic alkenes and linear alkenes with trialkylsilanes in the presence of Lewis acid catalysts under mild conditions gave the corresponding (trialkylsilyl)alkanes in fair to good yields. The reaction of 1-methylcyclohexene with triethylsilane at -20 degrees C gave cis-1-triethylsilyl-2-methylcyclohexane with regio- and stereoselectivity via a trans hydrosilylation pathway. Cycloalkenes having an alkyl group at the double-bonded carbon showed better reactivity than nonsubstituted compounds in the Lewis acid-catalyzed hydrosilylation. The catalytic reactivity of Lewis acids decreases in the following order: AlBr3 > AlCl3 > HfCl4 > EtAlCl2 > ZrCl4 > TiCl4. When triorganochlorosilane was used as an activator in the aluminum chloride-catalyzed reaction, the hydrosilylation rate drastically increased. The results are consistent with a stepwise mechanism proceeding via the formation of a trialkylsilylenium ion intermediate.