[S:1]1(=[O:13])(=[O:12])[C@@H:5]2[CH2:6][C:7](=[O:8])[N:4]2[C@@H:3]([C:9]([OH:11])=[O:10])[CH2:2]1.C(N(C(C)C)CC)(C)C.[C:23]([O:29][CH2:30]Cl)(=[O:28])[C:24]([CH3:27])([CH3:26])[CH3:25].[I-].[Na+]>CN(C)C=O.C(OCC)(=O)C.O>[S:1]1(=[O:13])(=[O:12])[C@@H:5]2[CH2:6][C:7](=[O:8])[N:4]2[C@@H:3]([C:9]([O:11][CH2:30][O:29][C:23](=[O:28])[C:24]([CH3:27])([CH3:26])[CH3:25])=[O:10])[CH2:2]1To a stirred solution of 2.05 g of (3S, 5R)-penam-3-carboxylic acid 1,1-dioxide in 10 ml of N,N-dimethylformamide is added 1.30 g of diisopropylethylamine followed by 1.50 g of chloromethyl pivalate and 50 mg of sodium iodide at ca. 0° C. The reaction mixture is stirred at ca. 0° C. for 30 minutes and then at room temperature for 24 hours. The reaction mixture is then diluted with ethyl acetate and water and the pH of the aqueous phase is adjusted to 7.5. The ethyl acetate layer is separated and washed three times with water and once with saturated sodium chloride solution. The ethyl acetate solution is then dried using anhydrous sodium sulfate, and evaporated in vacuo to give the title compound.
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