Formal Allylic C(sp 3 )−H Carboxylation With CO 2 via Copper Metallaphotoredox Catalysis

ABSTRACT Catalytic carboxylation of ubiquitous C─H bonds with CO 2 has been demonstrated as a sustainable and streamlined pathway to valuable carboxylic acids. However, the catalytic carboxylation of abundant allylic C(sp 3 )─H bonds with CO 2 , which presents a unique opportunity to synthesize structurally diverse 3‐butenoic acids, still remains challenging. Herein, we report the first copper metallaphotoredox‐catalyzed formal allylic C(sp 3 )─H carboxylation with CO 2 , enabling efficient and selective synthesis of 3‐butenoic acids under mild and redox‐neutral conditions. This strategy lies in combining highly reducing photocatalysts to generate alkene radical anion intermediates with copper catalysis to orchestrate regioselective elimination, providing a distinct pathway from traditional allylic C(sp 3 )─H functionalization via forming allyl‐metal intermediates. This method features high atom and step economy, broad substrate scope, good functional group tolerance, facile scalability, and easy access to valuable compounds, including diverse bioactive molecules, natural products, and 13 C‐labeled anti‐inflammatory drug sulindac.