A new method for constructing pyrido[3',2':4,5]imidazo[1,2-b]pyridazine system and preparation of its derivatives

A new method for the construction of the pyrido[3',2':4,5]imidazo[1,2-b]pyridazine system involves the use of 2-chloro-3-nitropyridine and 6-chloropyridazin-3(2H)-one as the starting reactants. The key step is the POCl₃-promoted cyclization of the intermediate 2-(3-aminopyridin-2-yl)-6-chloropyridazin-3(2H)-one. The 2-positioned chlorine atom in the thus obtained 2-chloropyrido[3',2':4,5]imidazo[1,2-b]pyridazine can be replaced by a variety of nucleophiles.