Regioselective hydroborations of methylvinylchlorosilanes

Abstract

The regioselectivity of the hydroboration of the methylchlorovinylsilanes, Cl n Me 3− n SiCH CH 2 ( n= 0 − 3), has been investigated using BH 3←THF, 9-BBN, disiamyl- and dicyclohexylborane. Methylation of the adducts with methylmagnesium bromide is complicated by formation of tetraalkylboronates. Alkaline hydrogen peroxide oxidation of the boronates gives reasonable yields of the corresponding α- and β-trimethylsilylethanols for n= 0 and 1. For n= 2 and 3, conversion of the adducts to the corresponding α- and β- deuteroethylsilanes by treatment with excess sodium methoxide in methanol- 0- d provides a more effective means of derivatization. Addition of the alkenes, n= 2 or 3, to excess BH 3←THF gives ca. 90% of the α-boro-organo-chlorosilanes. For all of the alkenes, the dialkylboranes give ca. 80% of the β-boron adducts.