Visible-light-driven alkene dicarboxylation with formate and CO 2 under mild conditions.

Low-cost formate salt was used as the reductant and part of the carboxyl source in a visible-light-driven dicarboxylation of diverse alkenes, including simple styrenes. The highly competing hydrocarboxylation side reaction was successfully overridden. Good yields of products were obtained under mild reaction conditions at ambient temperature and pressure of CO 2 . The dual role of formate salt may stimulate the discovery of a range of new transformations under mild and friendly conditions.