Photoredox‐Catalyzed Thiocyanative Cyclization of Biaryl Ynones to Thiocyanated Spiro[5.5]trienones: An External‐Oxidant‐ and Transition‐Metal‐Free Approach

Abstract

AbstractA photoredox‐catalyzed, efficient protocol for the direct insertion of a ‐SCN group onto spiro[5.5]trienoneviaa dearomative cascade cyclization of biaryl ynone with inexpensive NH4SCN has been developed, employing 4CzIPN as a potent photocatalyst under blue‐light irradiation without external oxidant. This scalable 6‐exo‐trig cyclization led to the cascade formation of C−C and C−S bonds and incorporate diverse thiocyanated spiro compounds with excellent yield (up to 92 %). Additionally, mechanistic investigations with fluorescence quenching, cyclic voltammetry, and radical scavenging are presented. Gram‐scale synthesis and further functionalization of thiocyanated compounds highlight the potential utility of this methodology.