Synthesis of novel heterocycles using 1,2,3‐triazole‐4‐carbohydrazides as precursors

Herein, we report the synthesis of various heterocyclic ring systems containing 1,2,3‐triazole from the reactions of acid hydrazides and commercially available reagents, using efficient and simple procedures. Reactions of certain 1,2,3‐triazole‐4‐carbohydrazides and α‐bromoketones in boiling ethanol afforded the corresponding hydrazones rather than the expected triazines. The hydrazones could also be synthesized in 85‐90% yield via an alternative pathway that involved the reaction of 1,2,3‐triazole‐4‐carbohydrazides and 4‐acetyl‐1,2,3‐triazoles in boiling ethanol containing glacial acetic acid. Reaction of one of the 4‐carbohydrazides with carbon disulfide, followed by the reaction with hydrazine hydrate, gave 4H‐1,2,4‐triazole‐3‐thiol in 73% yield, which further reacted with other α‐bromoketones in boiling ethanol to afford 7H‐[1,2,4]triazolo[3,4‐b][1,3,4]thiadiazines in 82‐84% yields. Additionally, reactions of certain carbohydrazides with ethyl 2‐cyano‐3,3‐bis(methylthio)acrylate gave 1‐aryl‐1H‐1,2,3‐triazole‐4‐carbohydrazides rather than the expected 1H‐pyrazole‐4‐carboxylates