Step 1: Preparation of tert-butyl 4-nitrobenzylcarbamate (C4)
4-Nitrobenzylamine hydrochloride (10 g, 53.0 mmol) was suspended in a mixed solvent of THF (150 mL) and water (13 mL) and cooled to 0 °C. Di-tert-butyl dicarbonate (11.6 g, 53.0 mmol) and N,N-diisopropylethylamine (27.7 mL, 159 mmol) were added sequentially under stirring. The reaction mixture was stirred at 0 °C for 30 min and then slowly warmed up to 25 °C and continued stirring for about 20 hours. Upon completion of the reaction, most of the THF was removed by concentration under reduced pressure. the residue was dissolved in EtOAc and washed sequentially with 1N HCl, saturated NaHCO3 solution and saturated NaCl solution. The organic phase was dried over anhydrous MgSO4, filtered and concentrated under reduced pressure to give the off-white solid product C4 (14.0 g, 99% yield).
1H NMR (400 MHz, d6-DMSO) δ: 8.16 (d, 2H), 7.55 (t, 1H), 7.46 (d, 2H), 4.21 (d, 2H), 1.36 (s, 9H).
