Aryl Carboxylic Acids as Structure-Tunable HAT Agents for Photochemical Site-Selective C(sp ³ )–H <i>gem</i> -Difluoroallylation of Amides

A photoredox-catalyzed strategy using aryl carboxylic acids as structure-tunable hydrogen atom transfer (HAT) agents is presented to enable the site-selective <i>gem</i>-difluoroalkenylation of C(sp³)-H bonds in amides under visible light. This redox-neutral method delivers up to 50:1 selectivity and 91% yield, tolerating diverse amide scaffolds and challenging α-trifluoromethyl alkyl alkenes. Late-stage functionalization of pharmaceuticals highlights its utility. Mechanistic studies reveal an aryl carboxyl radical-mediated HAT pathway, followed by radical addition, reduction, and β-fluoride elimination to furnish <i>gem</i>-difluoroalkenes.