[CH2:1]([N:3]1[C:11]([CH3:12])=[C:10]2[C:5]([CH:6]=[CH:7][C:8]([N:13]3[CH:18]=[CH:17][C:16](O)=[CH:15][C:14]3=[O:20])=[CH:9]2)=[N:4]1)[CH3:2].P(Br)(Br)([Br:23])=O.C(=O)([O-])O.[Na+]>CN(C)C=O>[Br:23][C:16]1[CH:17]=[CH:18][N:13]([C:8]2[CH:7]=[CH:6][C:5]3[C:10](=[C:11]([CH3:12])[N:3]([CH2:1][CH3:2])[N:4]=3)[CH:9]=2)[C:14](=[O:20])[CH:15]=1To a solution of 1-(2-ethyl-3-methyl-2H-indazol-5-yl)-4-hydroxypyridin-2(1H)-one (1.07 g) in N,N-dimethylformamide (20 ml) was added phosphorus oxybromide (1.37 g) at room temperature, and the mixture was stirred at 50° C. overnight. The reaction mixture was cooled to room temperature, saturated aqueous sodium hydrogen carbonate solution was added, and the mixture was extracted with ethyl acetate. The organic layer was washed with saturated brine, dried over anhydrous magnesium sulfate, and concentrated under reduced pressure. The obtained residue was recrystallized from ethanol-hexane to give the title compound (680 mg).
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