Exploration of N-hydroxy benzimidazole catalysts for hydrogen atom transfer reactions†

N-Hydroxy benzimidazoles (NHBIs) have proved to be efficient hydrogen atom abstractors (HAAs), but their further application in catalysis has been rarely explored since the first report. Herein, we describe their catalytic performance in other hydrogen atom transfer reactions. Specifically, we realized a copper/NHBI co-catalyzed synthesis of 2-phosphonopyrroles via cascade [3 + 2] annulation–aromatization. And NHBI was demonstrated to play a crucial role in both the annulation step and the subsequent aromatization. Besides, NHBI-catalyzed annulation with an imine and C–H oxidation were also feasible. Notably, NHBIs bearing a docking group that can recognize substrates were also investigated as bifunctional HAT catalysts for the first time.