CC[O-].[Na+].[C:5]([O:13]CC)(=O)[CH2:6][C:7]([O:9][CH2:10][CH3:11])=[O:8].[CH2:16]([N:18]1[C:23]2[N:24]=[C:25]([C:28]3[CH:33]=[CH:32][CH:31]=[CH:30][CH:29]=3)[N:26]=[CH:27][C:22]=2[C:21](=O)[O:20]C1=O)[CH3:17].Cl>CN(C)C=O>[CH2:10]([O:9][C:7]([C:6]1[C:5](=[O:13])[N:18]([CH2:16][CH3:17])[C:23]2[N:24]=[C:25]([C:28]3[CH:33]=[CH:32][CH:31]=[CH:30][CH:29]=3)[N:26]=[CH:27][C:22]=2[C:21]=1[OH:20])=[O:8])[CH3:11]To a 40 ml. solution of NaOEt (1.0 g. Na--0.042 mole) was added 6.8 g. (0.042 mole) of diethyl malonate and this is stirred 10 minutes, then stripped to dryness. Dimethylformamide was added until a solution formed and to this was added 5.7 g. (0.021 mole) of 1-ethyl-7-phenyl-2H-pyrimido[4,5-d][1,3]oxazine-2,4(1H)-dione and the mixture heated at reflux for 2 hours. The reaction was then cooled and poured into dilute HCl and the resulting precipitate filtered off and rinsed well with water. Recrystallization with hexane-ethyl acetate gave 5.1 g. of the title product--m.p. 177°-180° C.
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