[CH2:1]([O:8][C:9]([NH:11][C@H:12]([C:20]([OH:22])=O)[CH2:13]C1C=CC=CC=1)=[O:10])[C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][CH:3]=1.C([N:25](CC)CC)C.ClC(OCC)=O.[C:36]([O:39][CH2:40][CH3:41])(=[O:38])[CH3:37]>C(Cl)(Cl)Cl>[NH2:25][C@H:41]1[C@H:40]([O:39][C:36](=[O:38])[CH3:37])[NH:11][C:9]1=[O:8].[CH2:1]([O:8][C:9]([NH:11][C@H:12]1[C@H:13]([O:39][C:36](=[O:38])[CH3:37])[NH:25][C:20]1=[O:22])=[O:10])[C:2]1[CH:3]=[CH:4][CH:5]=[CH:6][CH:7]=1To a solution of N-benzyloxycarbonyl-L-phenylalanine (5.98 g, 20 mmol) and triethylamine (2.02 g, 20 mmol) in chloroform (100 ml), ethyl chloroformate (2.18 g, 20 mmol) was added at -15° C. The reaction mixture was stirred at a bath temperature of -10 to 5° C. for 1.5 hrs. Then a precooled (ca. -15° C.) solution of (3S,4S)-3-amino-4-acetoxy-azetidin-2-one in ethyl acetate, which was obtained from hydrogenation of (3S,4S)-3-benzyloxycarbonylamino-4-acetoxy-azetidin-2-one (see above), was added at -15° C. and stirring was continued at a bath temperature of -15 to 5° C. for 1 hr. After removal of solvent, the residue was dissolved in ethyl acetate, washed with water, brine and dried over sodium sulfate. After removal of solvent, the residue was purified by silica gel column chromatography using hexane-ethyl acetate (1:2) as eluent and the title compound was obtained as white solid.
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