Accessing thiophene-fused furans via visible light photoredoxcatalyzed [3+2]-annulation reaction

Abstract

A visible-light-driven [3+2] annulation of benzothiophenone-based diazo compounds with alkynes has been developed for the efficient synthesis of benzothiophene-fused furans. This photoredox-catalyzed transformation tolerates a broad range of alkynes, including those derived from natural products and bioactive molecules, affording an otherwise elusive class of fused heteroaryl scaffolds in moderate to acceptable yields. The scope of the methodology was further expanded to access a benzofuran-fused furan scaffold, underscoring its versatility in the synthesis of structurally diverse fused heterocycles. Based on several experimental observations, a plausible mechanistic pathway is proposed in which electron transfer between the excited photocatalyst and diazo compound plays a crucial role.