Rearrangements in a series of thiazol-2-ylsemicarbazides

Abstract

Treatment of 2-hydrazinothiazole (1) with methyl isocyanate gave 4-methyl-1-(thiazol-2-yl)semicarbazide (2), identical with the product obtained from 1-(methylcarbamoyl)thiosemicarbazide (4) and chloroacetaldehyde diethyl acetal. At room temperature 1-isopropylidene-2-(thiazol-2-yl)hydrazine (6a) and methyl isocyanate afforded 2-(isopropylidenehydrazono)-3-methylcarbamoyl-Δ⁴-thiazoline (7), but in boiling methyl cyanide a 2 : 1 mixture of the thiazoline (7) and the isomeric 1-isopropylidene-4-methyl-2-(thiazol-2-yl)semicarbazide (8) was obtained. Hydrolysis of the isopropylidene derivative (8) to 4-methyl-2-(thiazol-2-yl)semicarbazide (3) occurred during column chromatography on silica gel. The thiazoline (7) rearranged to give the isomeric thiazole (8) in boiling methyl cyanide, and was converted into the semicarbazide derivative (2) in boiling dilute hydrochloric acid.