Natural kaolin as an efficient recyclable catalyst for the synthesis of new 2,4-disubstituted quinolines

Substituted 2, 4- diphenyl quinolines were synthesized by a multicomponent domino reaction of anilines, aldehydes and terminal aryl alkynes. The synthetic pathway involves the formation of an imine, followed by the intermolecular addition of an alkyne to the imine. This intermediate immediately undergoes ring closure and oxidative aromatization. The reaction is catalyzed by natural kaolin, a strong, environmentally benign solid acid. In this procedure natural kaolin is used without any supporting. This catalyst- assisted microwave irradiation has oxidizing ability that leads to aromatization of final intermediate and produces the aromatic substituted quinolines without any other oxidizing agents. The multicomponent approach yields the products in excellent yields in a matter of minutes. The use of microwave activation reduces the reaction time significantly. No side-products are formed significantly. In addition one of the synthesized substituted quinolines is a new compound. However, this catalyst can be used for the synthesis of a variety of important heterocycles such as pyrrazoles, oxazolines, benzodiazepines and quinoxalines.