[O:1]1[CH:5]=[CH:4][C:3]([NH:6][C:7]2[C:8]([N+:18]([O-:20])=[O:19])=[C:9]3[CH2:17][O:16][CH2:15][CH2:14][C:10]3=[N+:11]([O-])[CH:12]=2)=[N:2]1.P(Br)(Br)Br.C(=O)([O-])[O-].[K+].[K+]>C(Cl)Cl>[O:1]1[CH:5]=[CH:4][C:3]([NH:6][C:7]2[C:8]([N+:18]([O-:20])=[O:19])=[C:9]3[CH2:17][O:16][CH2:15][CH2:14][C:10]3=[N:11][CH:12]=2)=[N:2]1To a solution of 473 mg of Compound 6 obtained in the above step (2) in 30 ml of methylene chloride is added a solution of 935 mg of phosphorus tribromide in 1 ml of methylene chloride under ice cooling. The reaction mixture is stirred for 2 hours, mixed with ice water and neutralized with aqueous potassium carbonate under ice cooling. The organic layer is separated, and the aqueous layer is extracted with methylene chloride. The organic layers are combined, washed with saturated saline, dried over anhydrous magnesium sulfate and the solvent is evaporated. The residue is recrystallized from methylene chloride-isopropanol to give 407 mg of the titled compound 7 as yellow crystals.
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