Metal‐Free Synthesis of 3‐Thiocyanatobenzothiophenes by Eosin Y Photoredox‐Catalyzed Cascade Radical Annulation of 2‐Alkynylthioanisoles

Abstract

A convenient, efficient, metal‐free synthesis of 3‐thiocyanatobenzothiophenes has been developed that uses eosin Y in a visible‐light‐mediated photoredox‐catalyzed anion oxidation of the ammonium salt of thiocyanate and proceeds through the cascade radical annulation of 2‐alkynylthioanisole at room temperature. The present protocol requires visible light as a green energy source, an organic dye as the photocatalyst, and oxygen as a green oxidant to provide a mild route with a broad substrate scope for the formation of potentially bioactive 3‐substituted benzothiophene derivatives in good yields.