C(O[C:4](=[O:21])[C:5]1[CH:10]=[CH:9][CH:8]=[N:7][C:6]=1[NH:11][C:12]1[CH:17]=[CH:16][CH:15]=[C:14]([N+:18]([O-:20])=[O:19])[CH:13]=1)C.O1CCCC1.[NH2-].[Na+].[CH2:29]([N:31]=[C:32]=[O:33])[CH3:30]>O>[N+:18]([C:14]1[CH:13]=[C:12]([N:11]2[C:6]3[N:7]=[CH:8][CH:9]=[CH:10][C:5]=3[C:4](=[O:21])[N:31]([CH2:29][CH3:30])[C:32]2=[O:33])[CH:17]=[CH:16][CH:15]=1)([O-:20])=[O:19]To a solution of 5.7 g of 2-(m-nitroanilino)nicotinic acid ethyl ester and 50 ml of dry tetrahydrofuran was added 1.1 g of sodium amide and the solution was stirred for one hour. To this was added dropwise under cooling 2.9 g of ethyl isocyanate and this mixture was reacted at 60°C for 10 hours. After the reaction was complete, the solvent was distilled off from the mixture, and to the residue obtained was added water to precipitate a crude product. This product was collected by filtration and recrystallized from methanol to give 3.4 g of 1-(m-nitrophenyl)-3-ethylpyrido[2,3-d]pyrimidine-2,4(1H,3H)-dione as colorless needles, melting at 210°-211°C.
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