C(N(CC)CC)C.[N:8]([CH:11]1[CH:14]([CH2:15][CH2:16][O:17][C:18](=[O:23])[C:19]([F:22])([F:21])[F:20])[NH:13][C:12]1=[O:24])=[N+:9]=[N-:10].[Si:25](Cl)([C:28]([CH3:31])([CH3:30])[CH3:29])([CH3:27])[CH3:26]>CN(C)C=O>[Si:25]([N:13]1[CH:14]([CH2:15][CH2:16][O:17][C:18](=[O:23])[C:19]([F:20])([F:21])[F:22])[CH:11]([N:8]=[N+:9]=[N-:10])[C:12]1=[O:24])([C:28]([CH3:31])([CH3:30])[CH3:29])([CH3:27])[CH3:26]Triethylamine (0.2 mol) is added dropwise to an ice-cold stirred solution of 3-azido-4-(2-trifluoroacetoxyethyl)-azetidin-2-one (0.2 mol) and t-butyldimethylsilyl chloride (0.2 mol) in dimethylformamide (100 ml). The resulting mixture is stirred for 10 min. in the cold and for 10 min at room temperature, and then evaporated under vacuum to remove DMF. The residue is taken up to methylene chloride, washed with water and brine, dried with magnesium sulfate, and evaporated under vacuum to provide N-(t-butyldimethylsilyl)-3-azido 4-(2-trifluoroacetoxyethyl)-azetidin-2-one.
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