Photocatalytic Decarboxylative Oxygenation of Unactivated Carboxylic Acids: A Review of Direct C–O Bond Formation

Photocatalytic decarboxylative oxygenation enables the construction of C-O bonds from carboxylic acids, which are versatile and sustainable precursors. This approach is characterized by mild reaction conditions, excellent functional group tolerance, and operational simplicity. This review systematically summarizes recent advances in photocatalytic decarboxylative oxygenation reactions, with a focus on methodologies that employ unactivated free carboxylic acids as radical precursors. We discuss a wide range of catalytic systems, including homogeneous transition-metal complexes (e.g., Ru, Ir, Fe, Cu, and Ce), metal-free organic photocatalysts, and heterogeneous carbon nitride materials, emphasizing their mechanisms and synthetic applications. The review also highlights emerging strategies such as ligand-to-metal charge transfer activation and photobiocatalytic cascades. Finally, we outline current challenges and future directions, including substrate scope expansion, selectivity control, mechanistic elucidation, and process scalability, underscoring the potential of this transformation in pharmaceutical synthesis, peptide modification, and sustainable molecular editing.