BF3·Et2O-Promoted Cleavage of the Csp–Csp2 Bond of 2-Propynolphenols/Anilines: Route to C2-Alkenylated Benzoxazoles and Benzimidazoles

A novel BF3·Et2O-promoted tandem reaction of easily prepared 2-propynolphenols/anilines and trimethylsilyl azide is developed to give C2-alkenylated benzoxazoles and benzimidazoles in moderate to good yields. Most reactions could be accomplished in 30 min at room temperature. This tandem process involves a Csp-Csp2 bond cleavage and a C-N bond formation. Moreover, both tertiary and secondary propargylic alcohols with diverse functional groups were tolerated under the mild conditions.