C([N-]C(C)C)(C)C.[Li+].[O:9]=[C:10]1[N:17]2[CH:12]([CH2:13][CH2:14][O:15][C:16]2([CH3:19])[CH3:18])[CH2:11]1.CN(C)[CH:22]=[O:23].[C:25](Cl)(=[O:27])[CH3:26].P([O-])([O-])([O-])=O>O1CCCC1>[O:9]=[C:10]1[N:17]2[CH:12]([CH2:13][CH2:14][O:15][C:16]2([CH3:19])[CH3:18])[C:11]1=[CH:22][O:23][C:25](=[O:27])[CH3:26]To a solution of 2.0 equivalents of freshly prepared lithium diisopropylamide in 5 ml anhydrous tetrahydrofuran under nitrogen atmosphere at -78° C. is added a solution of 8-oxo-2,2-dimethyl-3-oxa-1-azabicyclo[4.2.0]octane (98 mg., 0.629 mmmole) in 2 ml anhydrous tetrahydrofuran which has been cooled to -78° C. After two minutes excess anhydrous N,N-dimethylformamide (460 mg, 6.29 mmole) is added followed immediately by distilled and degassed acetyl chloride (148 mg, 1.89 mmole) which has been cooled to -78° C. After stirring at -78° for a period of 5 minutes, the reaction mixture is poured into 0.2M pH 7 phosphate buffer. The product is extracted with methylene chloride. The combined methylene chloride solutions are dried over magnesium sulfate, filtered and the filtrate evaporated under reduced pressure to give 64 mg of a colorless oil. Purification by preparative thick-layer chromatography on silica gel developing twice with ether gives 8 -oxo-7-acetoxy-methylene-2,2-dimethyl-3-oxa-1-azabicyclo[4.2.0]octane (25 mg).
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