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–RhIII–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.

This work discloses that a simple change in the anion of a copper(II) reagent along with the reaction solvent can dramatically alter the course of a Cp*Rh -catalyzed C-H activation-annulation reaction leading to completely switchable chemoselective products. The nature of the anion in terms of its coordinating ability and basicity, and also the polarity of the solvent have been found to be the crucial factors in the observed divergence.

Ring-fused cationic N-heterocycles are an important class of organic compounds recognized to be of significant interest in diverse research areas including bioactivity, materials chemistry, supramolecular chemistry, etc. Toward the synthesis of such molecules, recently unique chemistry has been explored utilizing a novel conjugative action of NHC ligands as a functionalizable directing group in rhodium(III)catalyzed aromatic/heteroaromatic/non-aromatic C-H activation and subsequent annulation of various imidazolium salts with internal alkynes. This review highlights the initial development and underscores the potential of this chemistry.

Disclosed herein is a rhodium(iii)-catalyzed novel one-step back-to-back double rollover annulation on pyridine and pyrazine backbones leading to structurally and optoelectronically diverse class of nicely decorated multi-ring-fused, extensively π-conjugated, N-enriched PAH molecules by virtue of orchestrated quadruple C–H activation events.