Visible-Light-Induced Annulation of Benzothioamides with Sulfoxonium Ylides To Construct Thiazole Derivatives

Herein, visible-light-induced annulation of benzothioamides with sulfoxonium ylides to furnish thiazole derivatives is developed under transition-metal-, photocatalyst-, and oxidant-free conditions. This protocol exhibits good substrate scope, affording the desired products with satisfied yields in a mild and green manner. Detailed mechanistic studies suggest that the benzothioamide substrate plays a dual role in this reaction. Under visible-light irradiation, excited benzothioamide, in its triplet state, could undergo S attack to the C═S moiety of the sulfoxonium ylide followed by the dissociation of dimethyl sulfoxide and H migration to give a key adduct. In addition, benzothioamide could act as an organocatalyst to facilitate the intramolecular cyclization of the adduct and proton transfer steps. After the dehydration of the cyclized intermediate, the desired thiazole derivatives can be produced.