[CH3:1][C:2]1[N:11]=[CH:10][C:9]([CH3:12])=[C:8]2[C:3]=1[CH:4]=[CH:5][C:6](=O)[NH:7]2.P(Br)(Br)([Br:16])=O.C(=O)(O)[O-].[Na+]>>[Br:16][C:6]1[CH:5]=[CH:4][C:3]2[C:8](=[C:9]([CH3:12])[CH:10]=[N:11][C:2]=2[CH3:1])[N:7]=1A mixture of 5,8-dimethyl-1,6-naphthyridin-2(1H)-one (2.1 g, 12 mmol) and phosphoryl tribromide (5 g) was heated to 110° C. for 1 h, cooled, diluted with ice water, and neutralized with saturated sodium bicarbonate solution. The aqueous phase was extracted with DCM (100 mL×3), and the combined organic layers were dried with sodium sulfate and purified by column chromatography to give 0.63 g of the product as a pale white solid. MS (ESI): m/z 237.0 [M+H]+.
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