Facile access to thieno[2,3-b]thiophenes and poly-substituted thiophenes through divergent annulation of ketene 1,3-dithietanes

A Lewis acid-catalyzed tandem nucleophilic addition/C-S cleavage/intramolecular annulation of ketene 1,3-dithietanes with aldehydes and photo-induced cycloaddition of ketene 1,3-dithietanes with alkynes were developed in this work. The readily available ketene 1,3-dithietanes were demonstrated as promising sulfur-containing synthons for the facile construction of the thiophene ring. Moreover, these processes feature simple operation, good functional group tolerance and mild reaction conditions. Also, the possible mechanisms are proposed in this study.