Solvent/Base-Cocontrolled Regiodivergent Synthesis of 5-Arylnaphtho[1',2':4,5]imidazo[1,2-a]pyridines and 3-Substituted 2-Arylimidazo[1,2-a]pyridines from 2-Arylimidazo[1,2-a]pyridines and α-Cl Ketones via a Rh(III)-Catalyzed C-H Activation Strategy.

A solvent/base-cocontrolled regiodivergent synthesis via a rhodium(III)-catalyzed C-H annulation and functionalization of 2-arylimidazo[1,2-a]pyridines with α-Cl ketones is disclosed. When using polar solvent 1,1,1,3,3,3-hexafluoro-2-propane (HFIP) with K2CO3, the C-H annulation selectively delivered 5-arylnaphtho[1',2':4,5]imidazo[1,2-a]pyridine. In contrast, a system with nonpolar solvent p-xylene with NaOAc predominately afforded 3-substituted 2-arylimidazo[1,2-a]pyridines via C3-H functionalization. The developed reaction methodology features a wide substrate scope and ideal functional group tolerance. It is also operationally simple and scalable. Furthermore, the photophysical properties of annulation products and further derivatizations of C3-H functional products demonstrate that this method has potential applications in photoelectric materials and organic synthesis. Through a combined computational and experimental mechanistic study, we delineate the distinct roles of the solvent and base.