An efficient and sustainable protocol for regioselective hydrocarboxylation of alkynes to construct diverse propionic acid derivatives is disclosed. Under photoinduced conditions, the anti-Markovnikov hydrocarboxylation of alkynes was realized with CO₂ radical anion in-situ generated from formate as both a carbonyl source and a reductant. The collaboration between photosensitizer and hydrogen atom transfer catalyst promoted the catalytic cycle to work smoothly, giving a broad substrate scope including terminal and internal alkynes. The Giese radical addition of CO₂ radical anion to the C—C triple bond is the key step to initiate the reaction.

Key words: formate, CO₂ radical anion, hydrocarboxylation, visible-light catalysis, aryl propionic acids