Photoredox/Sulfide Dual Catalysis for Modular Synthesis of Multi-Substituted Furan Rings via Catalytic Indirect Reductive Quenching

The catalytic indirect reductive quenching method is facilitated by a combination of Ir(III) photoredox and sulfide dual-catalysis system. This study demonstrated a method for synthesizing multi-substituted furans by using a photoredox/sulfide dual-catalysis system. This method enables the synthesis of various furan derivatives, including spirofurans and phthalans. The utility of this system was demonstrated through gram-scale synthesis of the pharmaceutical molecule talopram. Mechanistic studies and density functional theory calculations suggested the formation of sulfonium species via sulfide radical cations, followed by intramolecular cyclization to produce the desired furan derivatives.