[H-].[Na+].[Br:3][C:4]1[C:15](=[O:16])[NH:14][C:7]2[N:8]=[C:9]([S:12][CH3:13])[N:10]=[CH:11][C:6]=2[CH:5]=1.[CH2:17](Br)[CH3:18]>CN(C)C=O>[Br:3][C:4]1[C:15](=[O:16])[N:14]([CH2:17][CH3:18])[C:7]2[N:8]=[C:9]([S:12][CH3:13])[N:10]=[CH:11][C:6]=2[CH:5]=1To a suspension of NaH (60% in oil, 0.15 g, 3.75 mmol) in anhydrous dimethylformamide (10 mL) was added 6-bromo-2-(methylthio)pyrido[2,3-d]pyrimidin-7(8H)-one (2, 0.68 g, 2.50 mmol) at room temperature and the reaction was stirred at 50° C. for 0.5 h. The reaction mixture was cooled to room temperature, ethyl bromide (0.22 mL, 0.32 g, 2.93 mmol) was added, and the reaction was stirred at 50° C. for 1.5 h. The mixture was poured onto ice water (10 g), and the white precipitate was collected to give 6-bromo-8-ethyl-2-(methylthio)pyrido[2,3-d]pyrimidin-7(8H)-one (0.57 g, 1.90 mmol, 76%). ESMS m/z 300 (M+H)+. The material was used without any further purification.
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