Visible‐light‐promoted catalyst‐free benzylic C‐H oxidation using molecular oxygen as a green oxidant

Abstract Herein, we report a catalyst‐ and additive‐free strategy for the visible‐light‐promoted carbonylative oxidation of benzylic C‐H bonds employing molecular oxygen as the sole oxidant. This operationally simple protocol enables the conversion of a broad range of aromatic alkanes into valuable ketones, including complex drug derivatives and intermediates under mild conditions using ethyl acetate as a green solvent. Mechanistic studies reveal that the reaction proceeds via a substrate‐oxygen charge‐transfer (CT) complex upon photoexcitation, generating reactive oxygen species (singlet oxygen and superoxide anion) and a key benzylic radical. Interestingly, the carbonyl product can further accelerate the transformation by participating in a separate CT complex with the starting material. To address the scalability limitations, a novel solvent‐free continuous‐flow photoreactor was developed, which demonstrated a significant efficiency enhancement of over 150‐fold compared to batch processes. This work presents a green, practical, and scalable method for benzylic oxidation, underpinned by a detailed mechanistic understanding of the photoinduced CT process.