Visible Light‐Driven Photoredox Synthesis of Sulfonylated Benzimidazoisoquinolines via 10 H ‐Phenothiazine‐Catalyzed Electron Donor–Acceptor Complexes

An unmodified 10 H ‐phenothiazine is directly utilized as an efficient photocatalyst to enable ready access to sulfonylated benzo[4,5]imidazo[2,1‐ a ]isoquinoline derivatives from N ‐allyl benzimidazoles and sulfonyl chlorides. The reaction involves the formation of electron donor–acceptor complexes between phenothiazine and sulfonyl chloride, which, upon visible light irradiation, undergo single‐electron transfer to generate sulfonyl radicals. The reaction features mild conditions, broad substrate scope, and high efficiency.