A convenient new synthesis of fused 1,2,4-triazoles: the oxidation of heterocyclic hydrazones using copper dichloride

A series of 1,2,4-triazoles have been prepared by oxidative intramolecular cyclization of heterocyclic hydrazones with copper dichloride. General applicability of this simple transformation was confirmed by the synthesis of moderate to high yields of 1,2,4-triazolo[4,3-a]pyridines, 1,2,4-triazolo[4,3-a]pyrimidines, 1,2,4-triazolo[4,3-b]pyridazines, 1,2,4-triazolo[4,3-a]phthalazines, and 1,2,4-triazolo[4,3-a]quinoxalines. A 1,2,4-triazolo[4,3-e]purine-6,8(7H)-dione was obtained in a lower yield.