We report here selective formation of functionalized 1,4-dihydropyridines (DHP), acridinediones and polyhydroquinolines in high yields using amine-functionalized graphene oxide nanosheets (AFGONs) as the bifunctional catalyst. The method overcomes the limitations of previous protocols affording a mixture of DHP and pyridine derivatives using graphene oxide as the catalyst. The mild reaction conditions are found compatible with a wide range of functional groups. It is presumed that a cooperative effect between the acidic and basic functionalities present in AFGONs may have exerted high catalytic efficiency as well as prevented further oxidation to pyridine derivatives. A plausible mechanism is proposed on the basis of some control experiments. The reactions can be scaled up conveniently, and the catalyst can be recycled for five consecutive runs without loss of its activity.
Keywords: 1,4-Dihydropyridine; Amine-functionalized graphene oxide; Bifunctional catalyst; Hantzsch reaction; Multi-component reaction (MCR).