Synthesis and Aromatization of 1,4-Dihydropyridines in Water

A series of 1,4-dihydropyridines were synthesized in refluxing water by the reaction of aldehydes with ethyl acetoacetate and ammonium acetate without any additives. Then manganese dioxide was added to the reaction system to form the corresponding oxidized pyridine derivatives in one pot under refluxing conditions. Thus the two steps of synthesis and aromatization of Hantzsch 1,4-dihydropyridines were simplified by a one-pot process. Finally a series of pyridine derivatives were obtained by this straightforward and environmentally benign method.