Cascade C-H Activation and Defluorinative Annulation of 2-Arylbenzimidazoles with α-Trifluoromethyl-α-diazoketones: Modular Assembly of 6-Fluorobenzimidazo[2,1-a]isoquinolines.

A novel Ru-catalyzed redox-neutral [4+2] cyclization of 2-arylbenzimidazoles with α-trifluoromethyl-α-diazoketones has been achieved through sequential C-H activation and defluorinative annulation. This synthetic protocol unlocks modular and expeditious access to 6-fluorobenzimidazo[2,1-a]isoquinolines with high efficiency and excellent functional group compatibility. The resultant monofluorinated heterocyclic products can readily diversified by various nucleophiles.