1,2‐Fused pyrimidines. III. Derivatives of 12H‐pyrido[1′,2′:1,2]pyrimido[4,5‐b]quinoline, a novel heterocyclic system

Reactivities of 2‐amino‐4H‐pyrido[1,2‐a]pyrimidin‐4‐ones and 4‐amino‐2H‐pyrido[1,2‐a]pyrimidin‐2‐ones, both N,N‐dialkyl and (N‐alkyl, N‐phenyl)substituted, when treated with the N,N‐dimethylformamide/phosphorus oxychloride Vilsmeier‐Haack reagent XII were compared. Starting from 2‐[(N‐alkyl, N‐phenyl)amino] compounds IXa,b, the expected XVIa,b and XVIIa,b were obtained, which are derivatives of 12H‐pyrido[1′,2′:1,2]pyrimido[4,5‐b]quinoline, a novel heterocyclic system. When 2‐(phenylamino) compound IXc was used a mixture of 3‐formylderivative XVIII and 12H‐pyrido‐[1′,2′:1,2]pyrimido[4,5‐b]quinolin‐12‐one (XIX) resulted from the reaction. On the other hand, 2‐(dialkylamino)‐4H‐pyrido[1,2‐a]pyrimidin‐4‐ones IIIa‐c plainly afforded high yields of 3‐formylderivatives XIVa‐c. In contrast, no significant reaction occurred when 4‐(dialkylamino) and 4‐[(N‐alkyl,N‐phenyl)amino] compounds IIa‐c and VIIIa,b were treated with the reagent XII, under the same as well as more severe conditions. A clear difference in the nucleophilic reactivity of C‐3 position between these two classes of isomers is pointed out by the above summarized results.