Visible-Light-Induced Regioselective Benzylic CH Oxidation of Substituted 6-Aryl-7,8,9,10-tetrahydrobenzo[c]phenanthridine

A practical and sustainable protocol for the photocatalytic oxidation of benzylic CH bonds, particularly within polycyclic heteroaromatic (PHA) frameworks, has been developed. In contrast to many previously reported systems, which often rely on long reaction times, narrow-spectrum LEDs, additives, or specialized photoreactors or setups, this method employs inexpensive eosin Y under white LED illumination with molecular oxygen supplied via a balloon. The transformation proceeds under mild conditions without the need for transition metals, hazardous oxidants, or auxiliary additives, and operates via a radical mechanism supported by inhibition studies. The broad substrate tolerance and operational simplicity of this protocol facilitate efficient access to benzylic ketones. Its utility is exemplified in the synthesis of a variety of 6-aryl-8,9-dihydrobenzo[c]phenanthridin-10(7H)-one derivatives, where the substituent at the 6-position plays a critical role in determining product outcome. This method represents one of the few reported examples of late-stage CH functionalization in PHAs under photocatalytic conditions.