Base-Promoted [3 + 2] and [2 + 1] Annulation of Alkenyl Sulfonium Salts to Access 2-Oxazolines and Cyclopropanes

A base-promoted annulation reaction of alkenyl sulfonium salts with amides and acetophenones has been readily developed. This method enables the regioselective synthesis of various 2-oxazoline and cyclopropane compounds in good to high yields with a wide substrate scope and high functional group tolerance. Notably, this practical [3 + 2] or [2 + 1] annulation strategy circumvents the need for transition-metal catalysts, strong oxidants, and harsh reaction conditions, thereby enhancing its appeal in organic synthesis.