Synthesis of Fluorescent 1,3-Diarylated Imidazo[1,5-a]pyridines: Oxidative Condensation−Cyclization of Aryl-2-Pyridylmethylamines and Aldehydes with Elemental Sulfur as an Oxidant

Oxidative condensation-cyclization of aldehydes and aryl-2-pyridylmethylamines proceeded in the presence of a stoichiometric amount of elemental sulfur as an oxidant in the absence of catalyst. The reaction gave a variety of 1,3-diarylated imidazo[1,5-a]pyridines in good to high yields. The products showed fluorescence emission in a wavelength range of 454-524 nm. The quantum yields of 1,3-diarylated imidazopyridines were greatly improved compared to those of the parent 3-monosubstituted compounds.