Photocatalytic Difluoromethylation Cyclization and Dioxygen Trapping: Access to <i>gem</i> -Difluoro-Quinolines

Herein, a novel photocatalytic 6- exo - trig difluoromethylation cyclization and subsquent domino O 2 trap version is described. This protocol allows efficient access to structurally diverse 4-(hydroxymethyl)- gem -difluoro-quinolines under mild conditions. Broad substrate scope, good functional group compatibility, biologically active molecule modification, scale-up operation, and further derivatization demonstrate the utility of this protocol. A radical cyclization route was proposed based on radical inhibition experiments, deuterium-labeled experiments, visible-light irradiation on–off test, apparent quantum efficiency (AQE) calculation, and Stern–Volmer fluorescence quenching experiments.