Visible-Light-Induced Phosphonium Salt Catalysis for Site-Selective Aromatic C-H Halogenation and Chalcogenation.

A visible-light-induced phosphonium salt catalyzed approach to site-selective aromatic C-H halogenation and chalcogenation of arenes and heteroarenes is described. In this system, readily available phosphorus catalysts interact in situ with commercial halogenating and chalcogenating reagents to generate photoactive phosphonium salt species, which upon visible-light irradiation enable direct aromatic C-H chlorination, bromination, iodination, thiocyanation, selenocyanation, and trifluoromethylthiolation under mild conditions. The method avoids transition-metal participation and shows good site selectivity across a range of arenes and heteroarenes, including amino acid derivatives and selected bioactive molecules. Mechanistic experiments support the involvement of electron donor-acceptor (EDA) complex formation between the phosphine catalyst and the functionalization reagent, followed by photoinduced radical generation. This study establishes a visible-light phosphonium salt catalysis platform for the site-selective functionalization of aromatic frameworks relevant to amino acid derivatives and bioactive molecules.