CSA-catalyzed three-component synthesis of 6-aryl-6H-chromeno[4,3-b]quinolines

Abstract

Substituted chromeno[4,3-b]quinolines are an important class of moieties due to their activity and pharmaceutical relevance. A simple and efficient one-pot three-component protocol has been developed for the synthesis of diverse 6-aryl substituted 6H-chromeno[4,3-b]quinoline derivatives from aromatic anilines, salicylaldehydes, and cinnamaldehydes under (±)-camphorsulfonic acid catalysis. The optimised protocol offers significant potential for atom economy under mild conditions over the pre-existing multistep approaches. This method is operationally simple and well compatible with a wide range of substrates, with most derivatives forming a precipitate in the reaction mixture. This new approach is followed to perform gram-scale synthesis, achieve smooth results, and demonstrate its industrial applicability. Moreover, chromeno-quinoline frameworks have demonstrated significant potential as pharmacophores and functional materials. The aggregation behaviour of one of the compounds, 4o, was also studied in a THF/hexane solvent, along with concentration-dependent fluorescence spectroscopy. Absolute quantum yield was also measured in both THF and hexane.