Reductive coupling reactions of 2-nitrochalcones and their β-hydroxyanalogues:: New syntheses of 2-arylquinoline and 2-aryl-4-hydroxyquinoline derivatives

A one-pot synthesis of novel 2-arylquinolines and 2-aryl-4-hydroxyquinolines was developed from the intramolecular reductive coupling reactions of 2-nitrochalcones and 3-hydroxy-1-phenyl-3-(2-nitrophenyl)-2-propen-1-ones. Depending on the reduction method and on the presence of electron donating substituents on the A ring of 2-nitrochalcones one can modulate the formation of 2-arylquinolines, their N-oxides, and of 2-aminochalcones. The reduction of 3-hydroxy-1-(2-hydroxyphenyl)-3-(2-nitrophenyl)-2-propen-1-ones with stannous chloride in hydrochloric acid gave 2 '-aminoflavones and with ammonium formate and Pd/C yielded 2-(2-hydroxyaryl)-4-hydroxyquinolines.