To a solution of (R)-3-Boc-aminopyrrolidine (5.0 g, 26.8 mmol) in tetrahydrofuran (THF, 40 mL) was added triethylamine (3.7 mL, 26.8 mmol), followed by slow dropwise addition of benzyl chloroformate (3.8 mL, 26.8 mmol). The reaction mixture was stirred at room temperature for 24 hours before being filtered and the solvent was removed under vacuum. The residue was dissolved in ethyl acetate (EtOAc) and washed sequentially with 1N sodium bicarbonate solution (100 mL), 1.5N citric acid solution (100 mL) and water. The organic layer was dried over anhydrous magnesium sulfate (MgSO4) and concentrated to dryness in vacuum to afford benzyl (R)-3-tert-butoxycarbonylaminopyrrolidine-1-carboxylate (7.39 g, 86% yield). Thin-layer chromatography (TLC) Rf value was 0.41 (unfolding agent C); mass spectrometry (MS) showed a molecular ion peak m/z 321 (M+H)+; elemental analysis (C17H24N2O4) calculated values: C, 63.73; H, 7.55; N, 8.74; measured values: C, 63.51; H, 7.43; N, 8.65.
