[F:1][C:2]1[CH:3]=[C:4]([N:19]2[CH2:23][C@H:22]([CH2:24]OS(C)(=O)=O)[O:21][C:20]2=[O:30])[CH:5]=[CH:6][C:7]=1[N:8]1[CH2:13][CH2:12][N:11]([CH2:14][CH2:15][O:16][CH3:17])[C:10](=[O:18])[CH2:9]1.[N-:31]=[N+:32]=[N-:33].[Na+]>CN(C=O)C>[N:31]([CH2:24][C@@H:22]1[O:21][C:20](=[O:30])[N:19]([C:4]2[CH:5]=[CH:6][C:7]([N:8]3[CH2:13][CH2:12][N:11]([CH2:14][CH2:15][O:16][CH3:17])[C:10](=[O:18])[CH2:9]3)=[C:2]([F:1])[CH:3]=2)[CH2:23]1)=[N+:32]=[N-:33](5R)-3-(3-Fluoro-4-{4-(2-methoxyethyl)-3-oxopiperazin-1-yl}phenyl)-5-(methanesulfonyl-oxymethyl)oxazolidin-2-one (990 mg) was dissolved in dry DMF (30 ml), sodium azide (868 mg) was added, and the mixture heated at 80° C. for 4 hours. The mixture was evaporated to dryness, and the residue dissolved in ethyl acetate and washed with three portions of water. The aqueous layer was back-extracted with two portions of ethyl acetate, and the combined organic extracts dried over MgSO4. Evaporation gave (5R)-5-azidomethyl-3-(3-fluoro-4-{4-(2-methoxyethyl)-3-oxopiperazin-1-yl}phenyl)oxazolidin-2-one (770 mg) which was used without further purification.
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