-Hydroxybenzimidazole as a structurally modifiable platform for -oxyl radicals for direct C-H functionalization reactions.

Methods for direct functionalization of C-H bonds mediated by -oxyl radicals constitute a powerful tool in modern organic synthesis. While several -oxyl radicals have been developed to date, the lack of structural diversity for these species has hampered further progress in this field. Here we designed a novel class of -oxyl radicals based on -hydroxybenzimidazole, and applied them to the direct C-H functionalization reactions. The flexibly modifiable features of these structures enabled facile tuning of their catalytic performance. Moreover, with these organoradicals, we have developed a metal-free approach for the synthesis of acyl fluorides direct C-H fluorination of aldehydes under mild conditions.