[CH2:1]([C@H:8]1[CH2:12][O:11][C:10](=[O:13])[NH:9]1)[C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][CH:3]=1.C([Li])CCC.[C:19](Cl)(=[O:21])[CH3:20].[Cl-].[NH4+]>C1COCC1>[C:19]([N:9]1[C@@H:8]([CH2:1][C:2]2[CH:3]=[CH:4][CH:5]=[CH:6][CH:7]=2)[CH2:12][O:11][C:10]1=[O:13])(=[O:21])[CH3:20]10 g (56.4 mmol) of (4S)-4-benzyl-2-oxazolidinone is dissolved under argon atmosphere in 100 ml of abs. THF and is mixed dropwise at -78° C. with 37 ml (59.3 mmol, 1.6M in hexane, 1.05 eq) of n-butyllithium. After 10 min., 4.1 ml (4.5 g, 57.5 mmol, 1.02 eq) of acetyl chloride is instilled. The solution is stirred for 15 more min. under cooling and then 3 hours at room temperature. For working up it is mixed with 50 ml of saturated ammonium chloride solution, the organic solvents are distilled off in a vacuum and the remaining residue is extracted several times with ethyl acetate. After drying on sodium sulfate and concentration by evaporation in a vacuum, the remaining solid is recrystallized in ethyl acetate/hexane. 10.3 g (83%) of colorless needles with melting point of 106° C. is formed.
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