Lewis acid-catalyzed regio- and stereoselective allylsilation of simple unsaturated hydrocarbons

Abstract

The reactions of allylsilanes with unsaturated hydrocarbons such as alkenes and alkynes in the presence of Lewis acid catalyst give regio- and stereospecific trans-allylsilylated products in good yields. In the allylsilylations of terminal alkenes and alkynes, the silyl group adds to the terminal carbon and the allyl group adds to the inner carbon of the multiple bonds. Reaction with cyclic olefins gives allylsilylated products having the silyl and allyl groups in trans positions. In allylsilylations with the stereohomogeneous (Z)-crotyltrimethylsilane, an allylic inversion is observed indicating a stepwise allylsilylation process. The reaction of conjugated dienes with allylsilanes gives [3+2] annulation products having the silyl and the vinyl groups in trans positions on the ring. Allylsilylation of 5-(trimethylsilyl)-1-pentenes gives unusual allylsilylated products through an intramolecular 1,5-hydride rearrangement reaction in the normal allylsilylated products. All results are consistent with the involvement of silylenium ions in the allylsilylations.