N1C=CC=CC=1.[Si:7]([N:14]1[CH:17]([CH2:18][CH2:19][OH:20])[CH:16]([N:21]=[N+:22]=[N-:23])[C:15]1=[O:24])([C:10]([CH3:13])([CH3:12])[CH3:11])([CH3:9])[CH3:8]>C(Cl)Cl.[O-2].[O-2].[O-2].[Cr+6]>[Si:7]([N:14]1[CH:17]([CH2:18][CH:19]=[O:20])[CH:16]([N:21]=[N+:22]=[N-:23])[C:15]1=[O:24])([C:10]([CH3:12])([CH3:13])[CH3:11])([CH3:9])[CH3:8]Chromium trioxide (0.06 mol) is added to a solution of pyridine (0.12 mol) in methylene chloride (150 ml) and the mixture is stirred at room temperature for 15 min. A solution of N-(t-butyldimethylsilyl)-3-azido-4-(2-hydroxyethyl)-azetidin-2-one (0.01 mol) in methylene chloride (10 ml) is then added all at once. After stirring at room temperature for 5 min, the mixture is decanted and the dark, gummy residue is washed with more methylene chloride. The combined methylene chloride supernatant is concentrated under vacuum to a residue which is taken up in ether and filtered through celite. The filtrate is washed with 5% hydrochloric acid, 5% sodium bicarbonate solution, and brine, dried with magnesium sulfate, filtered, and evaporated under vacuum to yield N-(t-butyldimethylsilyl)-3-azido-4-(2-oxoethyl)azetidin-2-one.
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