Transition Metal and External Oxidant Free Visible Light Assisted Dearomatization of Biaryl Yones: Synthesis of Thiocyanated Spiro [5.5] Trienones

Abstract

A photoredox catalyzed efficient protocol for the direct insertion of -SCN group onto spiro[5.5]trienone via 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 investigation elaborated with fluorescence quenching, cyclic voltammetry, and radical scavenging study. Gram scale synthesis and further functionalization of thiocyanated compound highlighted the potential utility of this methodology.