[CH2:1]([CH:3]1[CH:6]([CH2:7][CH2:8][OH:9])[NH:5][C:4]1=[O:10])[CH3:2].[Mn]([O-])(=O)(=O)=[O:12].[K+].P([O-])(O)(O)=O.[K+].S(S([O-])=O)([O-])(=O)=O.[Na+].[Na+].S(=O)(=O)(O)O>O>[CH2:1]([C@@H:3]1[C:4](=[O:10])[NH:5][C@H:6]1[CH2:7][C:8]([OH:12])=[O:9])[CH3:2]The crude 3-ethyl-4-[2-(hydroxy)ethyl]-2-azetidinone (34 g; 0.237 mol) obtained according to step (c) is added to 63 g (0.394 mol) of potassium permanganate and 79 g (0.59 mol) of potassium dihydrogen phosphate in 870 ml of water. The mixture is maintained under stirring at 15° C. for 22 hours, then 220 ml of a saturated solution of sodium metabisulfite are added thereto maintaining the value of the pH at about 3 by the gradual addition of 220 ml of 10% sulfuric acid. The mixture is stirred under cooling at 5° C. until a clear solution is obtained (about 30 minutes), then, after saturation with ammonium sulfate, it is extracted with four 250-ml portions of ethyl acetate. The organic extracts are pooled together and dried over MgSO4. Concentration of the ethyl acetate solution to 100 ml and cooling overnight in a refrigerator gives a crystalline precipitate which is recovered by filtration. Yield 16.43 g of the product of the title. Concentration of the mother liquors yields 2.23 g of the product. Elemental analysis, I.R. and N.M.R. data are in agreement with the assigned structure.
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