To a solution of tert-butyl furan-3-ylcarbamate (4.2 g, 22.93 mmol) in anhydrous THF (160 mL) was added N,N,N',N'-tetramethylethylenediamine (4.3 mL, 28.49 mmol), and the resulting orange-colored solution was cooled to -30°C. n-Butyllithium (2.5 M in hexanes, 20.0 mL, 50.0 mmol) was added dropwise, and the resulting suspension was slowly warmed to 0°C within 1 h. The reaction mixture was cooled again to -30°C, followed by addition of dimethyl carbonate (5.75 mL, 68.0 mmol). mmol) and the resulting suspension was slowly warmed to 0°C over 1 h. The reaction mixture was again cooled to -30°C, followed by the addition of dimethyl carbonate (5.75 mL, 68.24 mmol), and then slowly warmed to 0°C over 45 min. Upon completion of the reaction, the reaction was quenched by the addition of a 2 M aqueous solution of HCl and the mixture was extracted with EtOAc. The organic layer was separated, dried over MgSO4 and concentrated in vacuum. The resulting residue was purified by column chromatography to afford methyl 3-((tert-butoxycarbonyl)amino)furan-2-carboxylate as a light yellow solid (4.60 g, 83%).1H NMR (300 MHz, CDCl3): δ 1.54 (s, 9H), 3.92 (s, 3H), 7.22 (bs, 1H), 7.38 (s, 1H), 8.18 (bs. 1H).
