Photocatalytic 1,4-Alkylation/Carboxylation of 1,3-Enynes with 4-Alkyl-Hantzsch Esters and CO2 for the Synthesis of 2,3-Allenoic Acids

Abstract Herein, a visible-light-promoted protocol for the regioselective 1,4-alkylation/carboxylation of 1,3-enynes with 4-alkyl-Hantzsch esters and CO2 is described. This approach enabled direct access to a diverse range of tetrasubstituted 2,3-allenoic acids in satisfactory yields. This transformation relies on readily available 4-alkyl-1,4-dihydropyridines as competent alkyl radical precursors, exhibits good functional group tolerance, and is amenable to 1 mmol scale synthesis. The utility of this method is further highlighted by the derivatization of the obtained allenoic acid products.