[CH2:1]([O:8][C:9]([NH:11][C@H:12]([C:14]([NH:16][C@H:17]1[C@H:20]([O:21][C:22](=O)[CH3:23])[NH:19][C:18]1=[O:25])=[O:15])[CH3:13])=[O:10])[C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][CH:3]=1.[Br:26]CCO.O>C1C=CC=CC=1.C1(C)C=CC=CC=1.O.O.C([O-])(=O)C.[Zn+2].C([O-])(=O)C>[CH2:1]([O:8][C:9]([NH:11][C@H:12]([C:14]([NH:16][C@H:17]1[C@@H:20]([O:21][CH2:22][CH2:23][Br:26])[NH:19][C:18]1=[O:25])=[O:15])[CH3:13])=[O:10])[C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][CH:3]=1
A mixture of (3S,4S)-3-(N-benzyloxycarbonyl-L-alanyl)amino-4-acetoxy-azetidin-2-one (1.36 g, 3.894 mmole), 2-bromoethanol (440 mg, 3.5 mmole), and zinc acetate dihydrate (642 mg, 2.9 mmole) in a mixture of benzene (40 ml) and toluene (40 ml) was refluxed for 5 hrs using Dean-Stark water separator. After cooling, the reaction mixture was partitioned between ethyl acetate (200 ml), acetone (25 ml) and water (150 ml). The organic layer was washed with water, brine and dried over sodium sulfate. After removal of the solvent, the residue was purified by silica gel column chromatography using ethyl acetate-hexane (2:1) as eluent and (3S,4R)-3-(N-benzyloxycarbonyl-L-alanyl)amino-4-bromoethoxy-azetidin-2-one was obtained (169 mg, 12% yield).
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