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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.