1,4-Dioxane hydrochloride → 4-{2-[(Hydrazinocarbonyl)oxy]ethyl}phenyl 2-(acetylamino)-1,3-thiazole-4-carboxylate hydrochloride

To a suspension of 2-[4-({[2-(acetylamino)-1,3-thiazol-4-yl]carbonyl}oxy)phenyl]ethyl tert-butyl hydrazine-1,2-dicarboxylate (371.6 mg, 0.800 mmol) in anhydrous dichloromethane (4 ml) was added 4M hydrogen chloride dioxane solution (4 ml). After stirring at room temperature for 2.5 hr, the reaction mixture was concentrated under reduced pressure. Ethyl acetate was added to the concentrated residue, and the mixture was concentrated again under reduced pressure. The operation was performed twice to remove hydrogen chloride gas azeotropically. The residue was suspended in a mixture of ethanol (5 ml) and ethyl acetate (30 ml), and the suspension was filtered. The filtered product was washed twice with ethyl acetate and dried under reduced pressure to give the title compound (317.7 mg, 0.793 mmol, yield 99.1%) as a white solid.