C-H Functionalization of Imidazo[1,5-]pyridines: A Metal-Free Approach for Methylene Insertion to Access C(sp)-C(sp)-H-C(sp) Bond Formation.

Formaldehyde has been used as a solvent and a source of carbon to insert a methylene group for bridging two imidazo[1,5-]pyridine molecules without using any metal catalysis. This strategy has been extended on other alkyl-, aryl-, and heteroaryl aldehydes as well. This C(sp)-C(sp)-H-C(sp) bond forming reaction proceeds via C(sp)H functionalization of imidazo[1,5-]pyridine and was applied on a wide range of substrates offering moderate to good yields of methylene-bridged/inserted bis-imidazo[1,5-]pyridines. Most importantly, as an application, the bis-heteroarene product has been demonstrated as a ligand. The ligand-like behavior of bis-imidazo[1,5-]pyridines has been demonstrated as an extension of current methodology. This reaction works well at the gram scale level.