Efficient Synthesis of 7H‐Chromeno[3,2‐c]quinolin‐5‐ium Salts and Quinolin‐4‐ones through Acid‐Promoted Cascade Reaction of 3‐Formylchromones and Anilines

Abstract

We report an efficient and environment‐friendly approach for the synthesis of multisubstituted 7‐oxo‐7H‐chromeno[3,2‐c]quinolin‐5‐ium salts using ambient air as a green sole oxidant. The chromeno[3,2‐c]quinolin‐5‐ium salts were prepared through metal‐free cascade intermolecular cycloaddition/oxidation reaction of 3‐formylchromones and N‐substituted anilines using HClO4 as the reagent and promoter under concise one‐pot conditions. In the applied research, the resulting quinolinium salts could serve as synthons and could be further transformed to diverse synthetically useful 3‐(2‐hydroxy‐benzoyl)quinolin‐4‐ones in water. This protocol offers a simple cascade strategy to synthesize a wide variety of natural‐like chromeno[3,2‐c]quinolin‐5‐ium salts and quinolin‐4‐ones, and shows some academic research potential as well as industrial applications.