Keller G. Guimarães

NHCs in Rhodium-Catalyzed C–H Activation–Annulation to Fused Imidazolium Salts

Significance: The increasing interest in N-heterocyclic carbenes (NHCs) arises arguably from their unprecedented stereoelectronic properties, strong metal–NHC bonding, and great stability of their metal complexes. NHCs act as both ligands and directing groups. These properties make NHCs useful in C–H functionalization as well as C–C and C–heteroatom bond-forming catalysis (see Review below). Reported here is the first directed intramolecular C–H functionalization–annulation reaction using a NHC–rhodium(III) complex as catalytic system. Thus, reaction of imidazolium salts 1 with internal alkynes 2, bearing different types of substituent groups, furnishes a variety of imidazo[1,2-a]quinolinium derivatives 3 in a onepot process in 35–93% yield.