Photocatalytic 1,4-Carbocarboxylation of 1,3-Enynes with CO₂

Herein, we report a photocatalytic regioselective 1,4-carbocarboxylation of 1,3-enynes with CO₂ enabled by a thiol-mediated hydrogen atom transfer (HAT) and formate cooperative mechanism. This strategy uses formate and CO₂ as synergistic carbon sources, to deliver a diverse array of aryl-, heteroaryl-, and alkyl-functionalized tetrasubstituted allene carboxylic acids. The reaction exhibits broad substrate scope across electronically and sterically varied enynes and iodides, and facilitates late-stage functionalization of bioactive molecules. Gram-scale synthesis and derivatization experiments further demonstrate its synthetic utility.