[N@:1]1([C:8]([O:10][CH2:11][C:12]2[CH:17]=[CH:16][CH:15]=[CH:14][CH:13]=2)=[O:9])[CH2:3][CH:2]1[C:4]([O:6][CH3:7])=[O:5].[C:18]1([CH:24]([OH:26])[CH3:25])[CH:23]=[CH:22][CH:21]=[CH:20][CH:19]=1.B(F)(F)F.CCOCC>ClCCl>[CH3:7][O:6][C:4](=[O:5])[CH:2]([NH:1][C:8]([O:10][CH2:11][C:12]1[CH:13]=[CH:14][CH:15]=[CH:16][CH:17]=1)=[O:9])[CH2:3][O:26][CH:24]([C:18]1[CH:23]=[CH:22][CH:21]=[CH:20][CH:19]=1)[CH3:25]To a stirred solution of 1-benzyl 2-methyl (S)-(−)-1,2-aziridinedicarboxylate (1.88 g) in dichloromethane (30 ml) were added at 0° C. 1-phenyl-ethanol (9.77 g) and boron trifluoride etherate (2.0 ml). After stirring the mixture for one hour the cooling bath was removed and stirring was continued overnight. Then the reaction mixture was poured onto saturated sodium bicarbonate solution and extracted with ethyl acetate. The combined organic layers were washed with brine, dried (MgSO4) and concentrated. The crude product was purified by column chromatography (SiO2; gradient: heptane/EtOAc 100:0->90:10) to give S)-2-benzyloxycarbonylamino-3-(1-phenyl-ethoxy)-propionic acid methyl ester (1.34 g, 47%) as a light yellow oil. MS (ISP): 358.2 ([M+H]+)).
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