Preparative Example U-1: Synthesis of tert-butyl N-(3-thienyl)carbamate. 3-Thiophenecarboxylic acid (2.50 g, 19.5 mmol), diphenylphosphoryl azide (4.62 mL, 21.5 mmol), and triethylamine (3.26 mL, 23.4 mmol) were dissolved in tert-butanol (50 mL). The reaction mixture was stirred under reflux conditions for 3.5 hours. Upon completion of the reaction, the reaction solution was cooled to 0 °C and the reaction was quenched by the addition of water. The reaction mixture was subsequently extracted with ethyl acetate and the organic layers were combined and washed with saturated brine. The organic layer was dried over anhydrous magnesium sulfate and concentrated under reduced pressure to remove the solvent. The residue was purified by silica gel column chromatography (eluent: petroleum ether/ethyl acetate=10:1) to afford tert-butyl N-(3-thienyl)carbamate (3.33 g, 16.7 mmol, 86% yield) as a white solid.1H-NMR (DMSO-d6) δ (ppm): 1.46 (9H, s), 6.97 (1H, d, J=5.2 Hz ), 7.16 (1H, s), 7.38 (1H, m), 9.61 (1H, s).
