Protonation of the triple bond of propargyl silanes with strong Brønsted acids results in formation of allyl carbenium ions 3 (Scheme 1). If R1 = H, deprotonation gives silyl dienes 5. In aryl substituted carbenium ions 6 both deprotonation and intramolecular attack to give silyl indenes 8 can occur. Selectivity is influenced by polarity of the solvent, electronic properties of aryl substituents and the Brønsted acid used. Activation of the triple bond with electrophilic halogen reagents results in allyl carbenium ions 10. Addition of the conjugate nucleophile gives allyl functionalized vinyl silanes 11. If a nucleophilic solvent is used, formation of vinyl silanes 12 is observed.