Transition-Metal- and Light-Free C–H (Trideutero)methylation of Quinoxalones Using (Deuterated) DMSO

A practical and environmentally benign protocol for the C–H methylation of quinoxalin-2(1H)-ones has been developed using dimethyl sulfoxide (DMSO) as both the methyl source and the reaction medium. Facilitated by Cs2CO3, this transition-metal- and light-free approach bypasses the need for specialized, toxic methylation reagents or radical initiators. The method is scalable and can be extended to C3-trideuteromethylation using DMSO-d6. Notably, under these conditions, N-benzyl quinoxalinones can be programmed to tandem C3-trideuteromethylation and benzylic C–H deuteration.