Brønsted Acid Catalyzed 1,2-Silyl Shift in Propargyl Silanes: Synthesis of Silyl Dienes and Silyl Indenes

A general method for generation of allyl carbenium ions from propargyl silanes via a 1,2-silyl shift by Brønsted acids is reported. Two possible reaction pathways are described. Deprotonation results in silyl dienes with yields from 52% to 92%. Intramolecular Friedel–Crafts reactions of aryl-substituted systems give access to silyl indenes with yields of 18–90% depending on the substitution pattern. The obtained products have been shown to react as alkenyl silanes in Hiyama coupling and electrophilic substitution and as dienes in Diels–Alder cycloaddition.