Synthesis and Reactions of the Novel 6-ethyl-4-hydroxy-2,5-dioxo-5,6-dihydro-2H-pyrano[3,2-c]quinoline-3-carboxaldehyde

Abstract

The novel 6-ethyl-4-hydroxy-2,5-dioxo-5,6-dihydro-2H-pyrano[3,2-c]quinoline-3-carboxaldehyde (2) was efficiently synthesized from Vilsmeier–Haack formylation of 3-(1-ethy1-4-hydroxy-2-oxo-(1H)-quinolin-3-yl)-3-oxopropanoic acid (1). The aldehyde 2 was allowed to react with some nitrogen nucleophiles producing a variety of hydrazones 3–7. Reaction of aldehyde 2 with hydrazine hydrate and hydroxylamine hydrochloride afforded pyrazole and isoxazole annulated pyrano[3,2-c]quinoline-2,5(6H)-dione, respectively. The reactivity of aldehyde 2 was examined toward some active methylene nitrile, namely, malononitrile, ethyl cyanoacetate, and cyanoacetamide leading to 2-iminopyrano[2′,3′:4,5]pyrano[3,2-c]quinolines 10–12, respectively. Also, some novel pyrazolo[4″,3″:5′,6′]pyrano[2′,3′:4,5]pyrano[3,2-c]quinolines (13, 14) and thiazolo[5″,4″:5′,6′]pyrano[2′,3′:4,5]pyrano[3,2-c]quinolines (15, 16) were synthesized. Structures of the new synthesized products were deduced on the basis of their analytical and spectral data.