C–H Functionalization\nof Imidazo[1,5‑<i>a</i>]pyridines: A Metal-Free Approach\nfor Methylene Insertion\nto Access C(sp<sup>2</sup>)–C(sp<sup>3</sup>)–H–C(sp<sup>2</sup>) Bond Formation

Formaldehyde has\nbeen used as a solvent and a source of carbon\nto insert a methylene group for bridging two imidazo[1,5-<i>a</i>]pyridine molecules without using any metal catalysis. This strategy\nhas been extended on other alkyl-, aryl-, and heteroaryl aldehydes\nas well. This C(sp<sup>2</sup>)–C(sp<sup>3</sup>)–H–C(sp<sup>2</sup>) bond forming reaction proceeds via C(sp<sup>2</sup>)H functionalization\nof imidazo[1,5-<i>a</i>]pyridine and was applied on a wide\nrange of substrates offering moderate to good yields of methylene-bridged/inserted\nbis-imidazo[1,5-<i>a</i>]pyridines. Most importantly, as\nan application, the bis-heteroarene product has been demonstrated\nas a ligand. The ligand-like behavior of bis-imidazo[1,5-<i>a</i>]pyridines has been demonstrated as an extension of current methodology.\nThis reaction works well at the gram scale level.