General procedure for the synthesis of methyl 3-aminofuran-2-carboxylate from methyl 3-((tert-butoxycarbonyl)amino)furan-2-carboxylate: To a solution of methyl 3-((tert-butoxycarbonyl)amino)furan-2-carboxylate (13.5 g, 55.96 mmol) in dichloromethane (100 mL) was added trifluoroacetic acid (TFA, 50 mL). The reaction mixture was stirred at room temperature for 5 hours. Upon completion of the reaction, the crude product was concentrated to dryness under reduced pressure. The residue was dissolved in dichloromethane (200 mL) and washed with saturated aqueous sodium bicarbonate (NaHCO3) (3 x 100 mL). The organic layer was dried over anhydrous magnesium sulfate (MgSO4), filtered and concentrated to dryness under reduced pressure. The resulting residue was purified by fast column chromatography (silica gel, eluent methanol/chloroform, gradient 0 to 20%) to afford methyl 3-aminofuran-2-carboxylate (7.89 g, 100%) as a light yellow oil.1H NMR (300 MHz, CDCl3) δ 7.26 (d, J = 1.9 Hz, 1H), 6.13 (d, J = 2.0 Hz, 1H ), 4.51 (s, 2H), 3.88 (s, 3H). Mass spectrum (ES+): m/z 164.2 ([M + Na]+).
