K2S2O8-Promoted C3-Bromination of Heteroarenes with Sodium Bromide.

A K2S2O8-promoted C3-bromination of heteroarenes using sodium bromide was developed. This method provides efficient access to a broad array of C3-brominated heteroarenes, including quinoxalin-2(1H)-ones, cinnolin-4(1H)-ones, coumarins, and oxazinone derivatives, in moderate to good yields (38 examples). Notably, this approach is applicable to both the late-stage functionalization of complex pharmaceutical agents and gram-scale synthesis. Mechanistic studies indicate that trifluoroacetic acid plays a crucial role in the reaction.