Harnessing CO2 in organic synthesis via photo- and electrocatalysis.

Carbon dioxide, an abundant, non-toxic, and renewable C1 source, has attracted significant attention as a sustainable feedstock in organic synthesis, offering dual benefits of CO2 utilisation and greenhouse gas minimisation. Despite the thermodynamic stability and kinetic inertness of CO2, which have long posed challenges for conventional transition-metal-based approaches, the field has undergone a paradigm shift. The open-shell catalysis driven by single-electron transfer (SET) processes has emerged as an alternative. In this review, we provide a comprehensive overview of recent mechanistic advances in photo- and electrochemically driven CO2 valorisation, organised around four key synthetic domains: (i) regioselective carboxylation of olefins, arenes and alkynes; (ii) radical-mediated lactonisation; (iii) homolytic C(sp3)-H/X functionalisation via hydrogen/halogen atom transfer (HAT)/(XAT); and (iv) oxidative alkene cleavage strategies. We further examine the complementary nature of photoredox and electrochemical strategies through the lens of intermediate generation, catalyst design, and reaction engineering.