Organophotoredox‐Catalyzed Annulation of Enamines with Sulfoxonium Ylides to Access Pyrroles via Radical Chain Mechanistic Scenarios

Comprehensive Summary Herein, organophotoredox‐catalyzed annulation of enamines with sulfoxonium ylides to construct pyrrole derivatives is developed under transition‐metal‐free and mild condition. A broad range of readily accessible substrates are suitable for this protocol, providing a convenient and efficient approach to preparing pyrrole derivatives with satisfying yields. Mechanistically, a photoredox‐mediated radical chain mechanistic pathway is proposed for this reaction by a synergistic experimental and computational study. Two key radicals, α ‐imino and α ‐carbonyl C‐radicals derived from enamines and sulfoxonium ylides, respectively, could be generated via two steps of single‐electron transfer in a photoredox catalytic loop. Subsequently, the formed α ‐carbonyl C‐radical may attack the alkenyl moiety of enamines. Next, the formed radical adduct could undergo H‐atom transfer with sulfoxonium ylides to regenerate the key α ‐carbonyl C‐radical and thus fulfill the chain propagation process. The afforded adduct intermediate could undergo an intramolecular cyclization followed by dehydration to furnish the desired pyrrole derivatives.