ClC(Cl)(Cl)COC(=O)C([N:8]1[C@H:11]([S:12][C:13](=[O:15])[CH3:14])[C@@H:10]([O:16][CH3:17])[C:9]1=[O:18])=O>CO.C(OC)(=O)C.O>[C:13]([S:12][C@H:11]1[NH:8][C:9](=[O:18])[C@@H:10]1[O:16][CH3:17])(=[O:15])[CH3:14]A solution of 1.52 g of 2-[(3S,4R)-4-acetylthio-3-methoxy-2-oxoazetidin-1-yl]-2-oxoacetic acid 2,2,2-trichloroethyl ester (crude product) in 290 ml of methanol, 40 ml of methyl acetate and 5.9 ml of water is refluxed for 20 minutes under nitrogen. The solvent is evaporated off in vacuo. After chromatography over silica gel with toluene/ethyl acetate (3:1) the residue yields the title compound.
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