Rhodium(III)-Catalyzed Nonaromatic sp2 C–H Activation/Annulation Using NHC as a Directing and Functionalizable Group

In parallel to the directing-group-assisted sp2 C–H bond activation–functionalization of aromatic backbones, a similar exercise with nonaromatic sp2 C–H bonds is also in high demand in synthetic chemistry despite several challenges pertinent to the latter process. In the presented protocol, N-heterocyclic carbene (NHC) motifs, appended to nonaromatic sp2 C–H bond-containing organic molecules, have been used for developing a rhodium­(III)-catalyzed annulation reaction with internal alkynes to synthesize a class of imidazo­[1,2-a]­pyridinium architectures. Mechanistic studies highlight the directing role of the NHC ligand during the C–H activation process and intermediacy of the C–H-activated Rh-NHC metallacycle in the catalysis.