Ring closure reaction of 5-hydroxy-pyrido[2,3-d]pyrimidine-2,4,7-triones to benzo[b]pyrimido[4,5-h]1,6-naphthyridine-1,3,6-triones

N-Substituted aminouracils ( 1 ) react with malonates by cyclocondensation to 5-hydroxy-pyrido2,3-d]pyrimidine-2,4,7-triones ( 2 ), which give with triethylorthoformate and aniline 6-(phenylaminomethylene)-pyrido2,3-d]pyrimidine-tetraone ( 3 ). Halogenation of 2a - d (with R² = Me) with phosphorylchloride leads to 5,7-dichloro-pyrido2,3-d]pyrimidine-2,4-diones ( 4 ) by cleavage of the methyl group at N-8, whereas Vilsmeier reaction of 2 affords 5-chloro-6-formyl derivatives ( 6 ), which cyclize with arylamines to give benzob]pyrimido4,5-h] 1,6-naphthyridines ( 9 ). Compounds 9 were obtained independently by amination of the tosylates 5 to the 5-arylamino compounds 8 , and Vilsmeier formylation to yield 9 .