Benzyl chloroformate → Benzyl[3-(aminocarbonyl)-2-thienyl]carbamate

To a stirred solution of 2-aminothiophene-3-carboxamide (5 g, 35.2 mmol) in tetrahydrofuran (200 mL) under argon was added diisopropylethylamine (9.52 ml, 54.5 mmol) and benzyloxycarbonyl chloride (7.53 mL, 52.8 mmol). After stirring for 60 hours, more diisopropylethylamine (9.52 mL, 54.5 mmol) and benzyloxycarbonyl chloride (7.53 mL, 52.8 mmol) were added. After an additional 24 hours, the suspension was filtered and the resulting solution was concentrated to ˜30 mL and diluted with ethyl acetate (100 mL) The organic layer was washed sequentially with saturated aqueous sodium bicarbonate (3×40 mL), a 3:1 mixture of saturated aqueous sodium bicarbonate and water (40 mL), and brine (40 mL), dried with sodium sulfate, filtered, and concentrated. The resulting mixture of white solid and brown oil was triturated with a mixture of ethyl acetate (10 mL) and hexanes (10 mL), and then the solid was collected by filtration. Drying under vacuum afforded the title compound as a solid.