Immobilized piperazine on the surface of graphene oxide as a heterogeneous bifunctional acid-base catalyst for the multicomponent synthesis of 2-amino-3-cyano-4H-chromenes

Abstract

In this paper, immobilized piperazine on the surface of graphene oxide (piperazine-GO) was synthesized and characterized by different methods such as FT-IR, solid-state 29Si{1H} and 13C{1H} CP/MAS NMR, elemental analysis, TGA, TEM, FE-SEM, XPS, and TPD. Subsequently, it was used as a heterogeneous bifunctional acid-base catalyst for the efficient multicomponent reaction of malononitrile, different active compounds containing enolizable C−H bonds and various aryl/alkyl aldehydes in aqueous ethanol. A wide variety of 2-amino-3-cyano-4H-chromenes were synthesized in the presence of this heterogeneous catalyst in good to high yields and in short reaction times. The catalyst was easily separated and reused for at least six times without significant loss of activity. The acidic nature of GO improved the catalytic activity of the supported piperazine and also provided heterogeneity to the catalyst. Using aqueous ethanol as a green solvent, high turnover number (TON), facile catalyst recovery and reuse, simple work-up and generality of the method, make this protocol an environmentally benign procedure for the synthesis of the titled heterocycles.