[CH3:1][S:2][C:3]1[N:4]=[CH:5][C:6]2[CH:12]=[CH:11][C:10](=O)[NH:9][C:7]=2[N:8]=1.P(Cl)(Cl)([Cl:16])=O>>[Cl:16][C:10]1[CH:11]=[CH:12][C:6]2[CH:5]=[N:4][C:3]([S:2][CH3:1])=[N:8][C:7]=2[N:9]=1A suspension of 1.0 g (5.2 mmol) of 2-methylsulfanyl-8H-pyrido[2,3-d]pyrimidin-7-one (Example 5) in 10 mL of phosphorus oxychloride is heated under reflux for 1 hour. The resulting solution is cooled and concentrated to give a solid, which is triturated with cold water and filtered to give 1.05 g of crude product. Recrystallization from acetonitrile lives 0.76 g (69%) of the product, mp 201-203° C.
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