[CH2:1]([O:3][C:4]([C:6]1[NH:7][CH:8]=[C:9]([CH2:17][C:18]2[CH:23]=[CH:22][CH:21]=[C:20]([F:24])[C:19]=2[CH3:25])[C:10]=1[C:11]1[CH:16]=[CH:15][CH:14]=[CH:13][CH:12]=1)=[O:5])[CH3:2].[H-].[Na+].O.CC(=O)OCC.C[N:36](C=O)C>>[CH2:1]([O:3][C:4]([C:6]1[N:7]([NH2:36])[CH:8]=[C:9]([CH2:17][C:18]2[CH:23]=[CH:22][CH:21]=[C:20]([F:24])[C:19]=2[CH3:25])[C:10]=1[C:11]1[CH:16]=[CH:15][CH:14]=[CH:13][CH:12]=1)=[O:5])[CH3:2]To a solution of the compound of step 4 (6.748 g, 20.00 mmol) in 60 ml of anhydrous DMF under a nitrogen atmosphere at 0° C. was added sodium hydride (60% in mineral oil, 0.960 g, 24 mmol) in small portions. After stirring for 10 min at 0° C., the mixture was allowed to warm to room temperature over 15 min. After cooling to 0° C. again, 0-(2,4-dinitro-phenyl)-hydroxylamine (cf. C. Legault et al., J. Org. Chem. 68 (2003), 7119; P. H. Boyle et al., ARKIVOC (2003) (vii), 67; 4.779 g, 24.00 mmol) was added in small portions and the mixture was stirred at room temperature for 1 h. Water (250 ml) and EA (250 ml) were added and the organic phase was washed twice with 125 ml each of a 1 N sodium hydroxide solution and 125 ml of brine, dried over magnesium sulfate, filtered and evaporated to dryness under reduced pressure. The residue was purified by chromatography on silica gel, first eluting with cyclohexane/DCM (40:60, then 20:80, then 0:100), then with DCM/EA (97.5:2.5, then 95:5) to give 6.33 g of the title compound as a beige solid melting at 87-88° C.
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