Switching of "Rollover Pathway" in Rhodium(III)-Catalyzed C-H Activation of Chelating Molecules

Organic molecules containing imidazolium and pyridine backbone are of special interest in many branches of chemistry, and therefore, overcoming the scarcity of their catalytic functionalization protocol leading to structurally important derivatives is strongly desired. This study demonstrates an unprecedented bimodal C-H activation functionalization catalysis on such organic molecules which contain imidazolium motif (potential N-heterocyclic carbene donor) and pyridine in chelating fashion and difficult to functionalize by trivial C-H activation strategy. The unique feature of this protocol is a flip-flop NHC-directed pyridine rollover and pyridine-directed NHC-rollover C-H activation within a stable "NHC-Rh-III-pyridine" chelate platform followed by functionalization with internal alkynes to furnish structurally important annulated products. Electronic and steric factors play a key role in achieving such novel chemistry.