Arylcarboxylation of unactivated alkenes with CO2 via visible-light photoredox catalysis

Photocatalytic carboxylation of alkenes with CO2 is a promising and sustainable strategy to synthesize high value-added carboxylic acids. However, it is challenging and rarely investigated for unactivated alkenes due to their low reactivities. Herein, we report an unprecedented visible-light photoredox-catalyzed arylcarboxylation of unactivated alkenes with CO2, delivering a variety of tetrahydronaphthalen-1-ylacetic acids, indan-1-ylacetic acids, indolin-3-ylacetic acids, chroman-4-ylacetic acids and thiochroman-4-ylacetic acids in moderate-to-good yields. This reaction features high chemo- and regio-selectivities, mild reaction conditions (1 atm, room temperature), broad substrate scope, good functional group compatibility, easy scalability and facile derivatization of products. Mechanistic studies indicate that in-situ generation of carbon dioxide radical anion and following radical addition to unactivated alkenes might be involved in the process

以二氧化碳（CO₂）与烯烃为底物的光催化羧化反应，是合成高附加值羧酸的极具前景且可持续的策略。然而，未活化烯烃（unactivated alkenes）因反应活性较低，针对该类底物的此类反应极具挑战性且相关研究鲜有报道。本文报道了一种前所未有的可见光光氧化还原催化未活化烯烃芳基羧化反应，以二氧化碳为羧源，可获得中等至良好收率的多种四氢萘-1-基乙酸、茚满-1-基乙酸、吲哚啉-3-基乙酸、色满-4-基乙酸及硫代色满-4-基乙酸类产物。该反应具有化学选择性与区域选择性优异、反应条件温和（1个标准大气压，室温）、底物适用范围广、官能团兼容性良好、易于放大生产且产物可便捷衍生化等特点。机理研究表明，该反应过程可能涉及二氧化碳自由基阴离子的原位生成，以及后续向未活化烯烃的自由基加成步骤。