Synthesis of Isocoumarins via Light‐Driven Carboxylative Cyclization Reaction of <i>o</i> ‐Ethynyl Aryl Bromides with CO ₂

Isocoumarins are an important class of bicyclic lactones, which are seen in natural products, drugs, and bioactive compounds, and a variety of synthetic methods for isocoumarins have been developed. However, the synthesis of isocoumarins via the catalytic CO₂ fixation has been scarcely reported despite the potential incorporation of CO₂ into the lactone moiety. Here, we developed the light-driven carboxylative cyclization reaction of o-ethynyl aryl bromides with CO₂, which selectively produced isocoumarins. Control experiments revealed that photoirradiation promoted the cyclization process with high selectivity.