Photocatalytic bifunctionalization of indole to access multi-substituted benzopyrrolizidinones

Abstract

Conventional methods for the synthesis of benzopyrrolizidinone skeletons with various biologically active molecules typically require multi-step sequential conversions, high loading catalysts and harsh conditions. Therefore, developing novel, highly selective and efficient catalytic methods for the synthesis of benzopyrrolidones remains important and challenging. Herein, a novel platform is established for rapidly diversifying multisubstituted benzopyrrolizidinones under mild conditions. This method involves an iridium-catalyzed, triphenylphosphine-mediated N–O bond cleavage to generate iminyl radicals, radical transposition through C–C bond cleavage, radical dearomatization and a precise radical–radical coupling sequence, thus facilitating the bifunctionalization of indole. The protocol features broad substrate scope and high yield. Notably, the methodology enables the construction of consecutive quaternary carbon atoms.