Imidazo pyridine skeleton

The reaction with pyridone (167) was interpreted as proceeding by the formation of the pyridone (168), followed by the Smiles rearrangement leading to the spiro compound (169), which by ring opening provides the pyrimidine derivative (170). In a subsequent cyclization step the pyrido-[1,2-aJpyrimidine skeleton (171) is formed, and finally hydrolysis of the imino group leads to the 6-oxo derivative (172). In the homologous imidazo-[l,2-n]pyridine series, the 5-iminoimidazo[l,2-c<]pyridine intermediate of type (171) could be isolated. 

Indeed, they are known for their anxiolytic, cardiovascular, analgesic, antihypertensive, and neuroleptic among other activities. These heteroclyclic skeleton forms the core structure of several drug molecules like zolpidem used in the treatment of insomnia, alpidem, an anxiolytic agent, olprinone for the treatment of acute heart failure, minodronic acid useful for the treatment of osteoporosis, and zolimidine used for the treatment of peptic ulcer. Besides, imidazo[l,2-a] pyridines and pyrimidines are also attractive due to their physicochemical properties such as fluorescent activity [128]. 

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