Hydrochloric Acid → tert-butyl 3-amino-1H-thieno[2,3-c]pyrazole-5-carboxylate

A mixture of tert-butyl 4-cyano-5-hydrazinothiophene-2-carboxylate (1.0 g, 4.2 mmol) and hydrochloric acid (0.7 mL of a 37% solution) in methyl alcohol (15 mL) was stirred at room temperature for 14 hours. The reaction mixture was diluted with ethyl acetate (50 mL) and washed with an aqueous solution of sodium bicarbonate. Organic layer was separated, dried over anhydrous sodium sulfate and evaporated to afford 0.9 g of the title compound.