A Sustainable Photocatalytic Regioselective Halogenation of 1-Alkyl/Benzyl-3-Phenylquinoxalin-2(1H)-ones in Aqueous Media

Abstract

A sustainable and regioselective protocol for mono-halogenation of 3-arylquinoxalin-2(1H)-ones has been developed, utilizing 1,3-dihalo-5,5-dimethylhydantoin derivatives as halogen sources. A dual catalytic system combining Pd(OAc)₂ and water-soluble Eosin Y was employed to achieve selective halogenation under visible-light irradiation in aqueous medium.Systematic optimization revealed the key role of water in enhancing yields, with the optimal conditions affording up to 89% yield across diverse substrates. Control experiments with radical scavengers, light on/off profiles, and thermal activation studies collectively validated a dual catalytic mechanism involving palladium-mediated C-H activation and photoredoxdriven generation of halogen radicals. Single-crystal X-ray diffraction confirmed the regioselectivity of functionalization, and the protocol was successfully scaled to gram quantities. This operationally simple, mild, and robust methodology demonstrates synthetic versatility and pronounced green credentials, establishing a new benchmark for sustainable C-H halogenation and functionalization of complex heterocycles.