1,2-FUSED PYRIMIDINES .5. SYNTHESIS OF 1-ALKYL-2H-DIPYRIDO(1,2-A-2',3'-D)PYRIMIDINE-2,5(1H)-DIONES OR 1-PHENYL-2H-DIPYRIDO(1,2-A-2',3'-D)PYRIMIDINE-2,5(1H)-DIONES

The reaction of 2-[(N-acyl, N-alkyl or phenyl)amino]4H-pyrido[1,2-a]pyrimidin-4-ones 8a-g with the N,N-dimethylformamide/phosphorus oxychloride Vilsmeier reagent 1 (95-degrees, 90 minutes) afforded 1-alkyl or phenyl-2H-dipyrido[1,2-a:2',3'-d]pyrimidine-2,5(1H)-diones, 3-alkyl substituted or not, 10a-g. The starting compounds 8 were prepared by treating 2-amino-4H-pyrido[1,2-a]pyrimidin-4-ones N-alkyl substituted 7a,b or N-phenyl substituted 4 with excess anhydrides (130-degrees, 7 hours); when the 2-(alkylamino) derivatives 7 were used in the reaction, compounds 8 were obtained along with very small amounts of 3-acyl-2-(alkylamino)-4H-pyrido[1,2-a]pyrimidin-4-ones 9.