Photocatalytic carboxylation of styrenes with CO2 via C=C double bond cleavage

Catalytic cleavage of C=C double bonds in alkenes is highly important to convert feedstocks into high-value compounds. However, these approaches are mainly limited to oxidative cleavage of alkenes with excess oxidants and redox-neutral alkene metathesis. In contrast, reductive C=C double bond cleavage and functionalization have not been reported. Herein, we report a novel visible-light photoredox-catalyzed carboxylation of styrenes with CO2 via reductive C=C double bond cleavage. The use of dicyclohexylmethylamine as scission reagent is the key to the success. Different from previous homologation reactions with CO2, this protocol enabled exchange of the carbon of styrenes with CO2, affording important aryl acetic acids via C=C double bond cleavage. Moreover, preliminary mechanistic investigation and DFT calculations shed light on the reaction mechanism, disclosing aminomethyl-carboxylation intermediate, benzylic radicals and carbanions as key intermediates in the reaction.