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

Abstract

Abstract Reactivities of 2‐amino‐4 H ‐pyrido[1,2‐ a ]pyrimidin‐4‐ones and 4‐amino‐2 H ‐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 12 H ‐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 12 H ‐pyrido‐[1′,2′:1,2]pyrimido[4,5‐ b ]quinolin‐12‐one ( XIX ) resulted from the reaction. On the other hand, 2‐(dialkylamino)‐4 H ‐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.