α-Amido Sulfonium Salts Provide a Platform for Photocatalytic Metal-Free Carbon-Carbon Bond Formation in Amides.

α-Amido sulfonium salts are bench-stable precursors of α-amidyl radicals, prepared directly from tertiary amides. These largely unexplored sulfonium salts engage in metal-free photocatalytic C(sp)-C(sp) and C(sp)-C(sp) bond formation in cross-coupling reactions that realize the formal α-alkylation, α-alkenylation, and α-arylation of amides. Fine-tuning the photocatalytic conditions allows divergent access to important 1,4-dicarbonyl compounds, skipped unsaturated amides, and α-heteroarylated amides, thus showcasing the role of α-amido sulfonium salts in establishing a novel platform for amide functionalization. Preliminary mechanistic experiments support a photocatalytic cycle in which the sulfonium salts are reduced to form α-amidyl radicals that couple with various electron-rich partners in a chemodivergent approach for the introduction of complexity in amides.