Cyclization of Semicarbazide Derivatives of 3-Methyl-5-thioxo-4,5-dihydro-1H-1,2,4-triazole-4-acetic Acid

By the reaction of hydrazide of 3-methyl-5-thioxo-4,5-dihydro-1H-1,2,4-triazole-4-acetic acid (1) with isocyanates, 3-methyl-5-thioxo-4,5-dihydro-1H-1,2,4-triazole-4-acetosemicarbazide derivatives 2 were obtained. Cyclization of these compounds in the presence of 2% NaOH led to the formation of 4,5-dihydro-1H-1,2,4-triazol-5-one derivatives 3, which was confirmed by X-ray analysis of 3b.