Ring Transformation of 1,3,4-Oxadiazole to s-Triazole-Fused Heterocycles. New Synthetic Route for Thiazolo-s-triazole and 7H-s-Triazolothiadiazine

Article abstract of DOI:10.1021/jo00135a014

s-Triazole-fused heterocycles have been synthesized by an intramolecular transformation of some 1,3,4-oxadiazole ketones with ammonia or hydrazine.The α-<(1,3,4-oxadiazol-2-yl)thio> ketone 2m gave thiazolo<2,3-c>-s-triazole (4m), accompanied by a small amount of the hydrazide 9m on treatment with ammonium acetate in acetic acid.Similar treatment of ketones 2a and 2b afforded only the hydrazides 9a and 9b, respectively.Ketones 2a-n reacted with hydrazine hydrate in acetic acid to give 7H-s-triazolo<3,4-b><1,3,4>thiadiazines 5a-n.However, ketones 2o-q, with substituents α to the carbonyl group, could not be converted to the corresponding fused-ring systems.Mechanisms for these transformations are proposed.