[C:1]1([N:7]2[C:12]3[N:13]=[CH:14][CH:15]=[CH:16][C:11]=3[CH2:10][NH:9][C:8]2=[O:17])[CH:6]=[CH:5][CH:4]=[CH:3][CH:2]=1.[CH3:18]N(C)C=O.[H-].[Na+].P(OC)(OC)(OC)=O>O>[C:1]1([N:7]2[C:12]3[N:13]=[CH:14][CH:15]=[CH:16][C:11]=3[CH2:10][N:9]([CH3:18])[C:8]2=[O:17])[CH:2]=[CH:3][CH:4]=[CH:5][CH:6]=1To a solution of 2.2 g of 1-phenyl-2-oxo-1,2,3,4-tetrahydropyrido[2,3-d]pyrimidine and 20 ml of dimethylformamide was added 0.5 g of approximately 50% sodium hydride, and the mixture was allowed to stand at room temperature for 30 minutes. To this was further added dropwise 4.2 g of trimethyl phosphate and the resulting mixture was heated at a temperature of 170° - 180° C in a sealed-tube for 7 hours. After the reaction was complete, the solvent was removed from the reaction mixture by distillation under reduced pressure. The residue thus obtained was diluted with water, extracted with ether and dehydrated. The ether was removed by evaporation to leave a residue. This residue was recrystallized from a mixture of ether and petroleum ether to yield 1.7 g of 1-phenyl-3-methyl-2-oxo-1,2,3,4-tetrahydropyrido[2,3-d]pyrimidine as colorless prisms, melting at 172° - 173° C.
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