Hydrochloric Acid → 1-[3-(3-Furyl)-1,2,4-thiadiazol-5-yl]piperazine

tert-Butyl 4-[3-(3-furyl)-1,2,4-thiadiazol-5-yl]piperazine-1-carboxylate (3.30 g, 9.81 mmol) was dissolved in ethyl acetate (50 ml), and a solution of 4 N hydrogen chloride in ethyl acetate (25 ml) was added thereto, followed by stirring at room temperature for 18 hours. Hexane (120 ml) was poured to the reaction mixture, and a solid was separated by filtration. The obtained solid was dissolved in an aqueous saturated sodium hydrogen carbonate solution, followed by stirring at room temperature for 2 hours. Water was poured to the reaction mixture, and the resulting solution was extracted with a mixed solution of ethyl acetate/tetrahydrofuran (1:1). The extract was washed with water and dried over anhydrous magnesium sulfate, and the solvent was distilled off under reduced pressure. Hexane was added to the residue, and 1.30 g (56.0%) of the desired product as a solid was separated by filtration.