A convenient preparation of [1,2,4]triazolo[1,5-a]pyridines from acetohydrazide derivatives. Synthetic and mechanistic aspects

Abstract

A novel synthesis of triazolo[1,5-a]pyridines (4) from 2′-acetyl-2-cyanoacetohydrazide (2) and arylidenemalononitriles (3) is described. The synthesis can be carried out either in one step or via 1-acetamidopyridones (5). Alternatively, acetylation of 1-aminopyridones (7) also gives triazolo[1,5-a]pyridines (4). Reaction of (2) with (3) in the presence of piperidine leads to the piperidinium salt of the triazolo[1,5-a]pyridine (6), which can be neutralized to give (4).