A catalytic intramolecular nitrene insertion into a copper(i)-N-heterocyclic carbene bond yielding fused nitrogen heterocycles.

N-(2-Azidophenyl)azolium salts were easily prepared and reacted with copper(i) under conditions allowing the formation of NHC complexes. Under these conditions, the formation of benzimidazo-fused heterocycles occurred under catalytic, efficient and very mild conditions. This reaction is proposed to proceed via dinitrogen elimination and imido/nitrene-NHC cyclization.