Bronsted Acid-Promoted Cyclizations of 1-Siloxy-1,5-diynes

摘要

Siloxy alkynes represent a versatile synthetic platform for the development of new C-C bond forming reactions.We previously established that soft and hard electrophiles (AuCl and HNTf_2) were capable of efficient activation of siloxy alkynes toward subsequent intramolecular additions of arenes and alkenes via the intermediacy of highly reactive ketenium ions.In this communication,we further expand this broadly useful reactivity concept and describe the discovery of the first Bronsted acid-promoted 5-endo-dig cyclizations of l-siloxy-l,5-diynes,which proceed with concomitant formation of C-Hal bonds as a result of halide abstraction from a halocarbon by the intermediate alkenyl cation.