Domino reactions between 6-ethyl-5,6-dihydro-4,5-dioxo-4H-pyrano[3,2-c]quinoline-3-carbonitrile and carbon nucleophilic reagents: Synthesis of novel heteroannulated pyridopyranoquinolines

A variety of novel heteroannulated pyrano[3,2-c]quinolines 2–12 was efficiently synthesized via a domino ‘Michael/retro-Michael/nitrile addition/heterocyclization’ reactions between 6-ethyl-5,6-dihydro-4,5-dioxo-4H-pyrano[3,2-c]quinoline-3-carbonitrile (1) and a diversity of carbon nucleophilic reagents. Pyrido[3′,2′:5,6]pyrano[3,2-c]quinolines 2–6 were synthesized from ring opening ring closure reactions of carbonitrile 1 with some methylene active nitrile namely malononitrile, cyanoacetamide, N-phenylcyanoacetamide, (phenylthio)acetonitrile and ethyl cyanoacetate, respectively. Reactions of carbonitrile 1 with dimer malononitrile and cyanoacetohydrazide showed different behavior producing the novel heteroannulated pyranoquinoline derivatives 7 and 8, respectively. Treatment of carbonitrile 1 with some methylene active ketones namely acetylacetone, acetoacetanilide, ethyl acetoacetate and ethyl benzoylacetate afforded pyrido[3′,2′:5,6]pyrano[3,2-c]quinolines 9–12, respectively. Structures of the synthesized products were deduced on the basis of their analytical and spectral data.