Curcumin‐Enabled Metal‐Free Photocatalytic Oxidation of Aryl‐ and Alkyl‐methanamines to Imines Under Green Conditions

Herein, we report a fully bio‐based, metal‐free photocatalytic protocol for the aerobic oxidation of aryl‐ and alkyl‐methanamines to imines under blue‐light irradiation. This transformation leverages curcumin, a naturally abundant and renewable polyphenol, as an efficient visible‐light photosensitizer and 2‐methyltetrahydrofuran (2‐MeTHF), a biomass‐derived solvent, establishing a sustainable catalytic system composed entirely of organic, bio‐derived components. The reaction proceeds efficiently at room temperature using molecular oxygen as the sole terminal oxidant, strictly avoiding transition metals, stoichiometric oxidants, and hazardous additives. A broad range of benzylic and aliphatic amines is converted to the corresponding imines in good to excellent yields (up to 98%), demonstrating the generality and practicality of the protocol. Comprehensive mechanistic investigations—including light on/off experiments, oxygen‐dependence studies, radical trapping, Stern–Volmer fluorescence quenching studies and Hammett analysis—support a sensitizer‐controlled aerobic photocatalytic pathway involving photoinduced electron transfer and oxygen‐mediated catalyst regeneration via superoxide radical anions. This work highlights the efficacy of natural pigments in driving high‐efficiency, sustainable organic transformations.