Using zirconium tetrachloride as the catalyst, a multicomponent tandem reaction of isatin, 1,3-dimethyl barbituric acid/1,3-indanedione and aliphatic alcohol, effectively gave the corresponding fused-ring compounds pyrimido[4,5-b]quino- lone-2,4-(1H,3H)-diones and 11H-indeno[1,2-b]quinolin-11-ones. The ester group was introduced into these nitrogen-containing molecules. All these newly synthesized compounds were identified by means of ¹H NMR, ¹³C NMR, IR and HRMS. Moreover, ethyl-1,3-dimethyl-2,4-dioxo-1,2,3,4-tetrahydropyrimido[4,5-b]quinoline-5-carboxylate (4q) was confirmed by X-ray single crystal diffraction analysis. Owing to the mild reaction conditions and simple easy available starting materials, the method for the preparation of the above two fused-ring skeletons is complementary to the existing methods, which can effectively enrich the corresponding heterocyclic compound library.

Key words: pyrimido[4,5-b]quinolin-2,4-(1H,3H)-dione, 11H-indeno[1,2-b]quinolin-11-one, fused-ring compound, multicomponent reaction, synthesis