[Cl:1][C:2]1[C:11](=O)[C:10]2[C:5](=[CH:6][CH:7]=[C:8]([O:13][CH3:14])[N:9]=2)[NH:4][CH:3]=1.P(Br)(Br)[Br:16].O.C(=O)([O-])[O-].[K+].[K+]>CN(C)C=O>[Br:16][C:11]1[C:2]([Cl:1])=[CH:3][N:4]=[C:5]2[C:10]=1[N:9]=[C:8]([O:13][CH3:14])[CH:7]=[CH:6]2To a solution of 3-chloro-6-(methyloxy)-1,5-naphthyridin-4(1H)-one (3-chloro-6-(methoxy)-1,5-naphthyridin-4-ol, for a synthesis see WO2004058144, Example 1(a)) (43 g, 204.8 mmol) in N,N-dimethylformamide (500 ml) at 0° C. was added phosphorous tribromide dropwise (23.3 ml, 245.8 mmol). The reaction mixture was then stirred at 10° C. for 0.5 hour and then at 25° C. for 1 hour. The mixture was then poured onto 1600 ml of water and basified to pH 7 with potassium carbonate. The solid formed was filtered off, washed with water and dried in vacuo to afford the desired compound (51 g, 91%).
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