Benzyl chloroformate → HCID 60204906, Verbindung

(2S)-4-Methylproline methyl ester (0.93 g (6.5 mmol), prepared as described in 2)) was dissolved in toluene (20 ml). To the solution were added an aqueous solution (20 ml) of sodium hydrogencarbonate (1.89 g, 22.5 mmol) and benzyl chloroformate (1.54 ml, 10.8 mmol), and the resulting mixture was stirred at room temperature overnight. The reaction mixture was extracted with ethyl acetate. The organic layer was washed with water and the solvent was removed by distillation under reduced pressure, to give (2S)-1-benzyloxycarbonyl-4-methylproline methyl ester (1.78 g) as a pale yellow oil (yield 99%). All of the compound obtained above was dissolved in tetrahydrofuran (30 ml). To the resulting solution was added lithium borohydride (0.28 g, 13 mmol) in three portions, and the resulting mixture was stirred at room temperature. Ice was added to the mixture and the mixture was stirred for 1 hour. The reaction mixture was extracted with ethyl acetate. The organic layer was washed with water, dried over anhydrous magnesium sulfate and the solvent was removed by distillation under reduced pressure. The residue was purified by column chromatography through silica gel (eluent, ethyl acetate:hexane=2:5), to give the title compound (1.07 g) as a pale yellow oil (yield 66%).