[CH2:1]([O:8][C:9]([NH:11][C@H:12]([C:14]([OH:16])=O)[CH3:13])=[O:10])[C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][CH:3]=1.C(N(CC)CC)C.ClC(OCC)=O.[NH2:30][C@H:31]1[C@H:34]([O:35][C:36](=[O:38])[CH3:37])[NH:33][C:32]1=[O:39]>ClCCl.C(OCC)(=O)C>[CH2:1]([O:8][C:9]([NH:11][C@H:12]([C:14]([NH:30][C@H:31]1[C@H:34]([O:35][C:36](=[O:38])[CH3:37])[NH:33][C:32]1=[O:39])=[O:16])[CH3:13])=[O:10])[C:2]1[CH:3]=[CH:4][CH:5]=[CH:6][CH:7]=1
To a solution of N-benzyloxycarbonyl-L-alanine (1.604 g, 7.188 mmole) and triethylamine (799 mg, 7.91 mmole) in dichloromethane (30 ml), ethyl chloroformate (738 mg, 6.83 mmole) was added at -15° C. The reaction mixture was stirred at -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 (see above) was added at -15° C. and the resulting mixture was stirred at 0° C. to room temperature for 2 hrs. After removal of solvent, the residue was dissolved in ethyl acetate, washed with cold saturated NaHCO3 solution, water, brine and dried over sodium sulfate. After removal of solvent, the residue was recrystallized from dichloromethane and (3S,4S)-3-(N-benzyloxycarbonyl-L-alanyl) amino-4-acetoxy-azetidin-2-one was obtained (1.36 g, 54% yield).
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