Preparation of 2-trimethylsilylmethyl-1-alkene; cross-coupling and protodesilylation sequence from 1,1-dibromo-1-alkene

A new method for the preparation of exomethylene type allylsilane is described. Selective mono-protodesilylation of 1-trimethylsilyl-2-trimethylsilylmethyl-2-alkenes 2 with PPTS afforded 2-trimethylsilylmethyl-1-alkenes 4 in excellent yields. Since the resulting allylsilanes 4 possess an exomethylene unit, the reactions of 4 with carbonyl compounds in the presence of Lewis acids gave the corresponding product 7 having an exomethylene unit in excellent yields.