Rapid Construction of an Imidazo[4,5-b]pyridine Skeleton from 2-Chloro-3-nitropyridine via Tandem Reaction in H2O-IPA Medium

A highly efficient, clean, and simple procedure for the synthesis of a privilege imidazo[4,5- b ]pyridine scaffold from 2-chloro-3-nitropyridine in combination with environmentally benign H 2 O-IPA as a green solvent is presented. The scope of the novel method has been demonstrated through the tandem sequence of S N Ar reaction with substituted primary amines followed by the in situ nitro group reduction and subsequent heteroannulation with substituted aromatic aldehydes to obtain functionalized imidazo[4,5- b ]pyridines with only one chromatographic purification step. The synthesis pathway appears to be green, simple, and superior compared with other already reported procedures, with the high abundance of reagents and great ability in expanding the structural diversity.