An efficient and environmentally benign domino protocol for the synthesis of spirodihydropyridines using europium-doped ZnO nanoparticles as recyclable and reusable heterogeneous catalyst

Abstract

An efficient and environmentally sustainable domino protocol has been presented for the synthesis of spirodihydropyridines with privileged heterocyclic substructures involving a three-component reaction of isatins, β-diketones and 1-naphthylamine using ethanol as a solvent and nanostructured Eu-doped ZnO as recyclable and reusable heterogeneous catalyst. X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy and Fourier transform infrared spectroscopy were used to characterise the nanostructured catalyst. The doping of europium with ZnO NPs increased catalytic efficiency and provided excellent yields of the products. The present synthetic protocol is most likely the first to explain the synthesis of spirodihydropyridines spiroannulated with chromenoquinolines, pyrimidoquinolines, indenoquinolines and acridines. The synthetic protocol is expected to be extended to synthesise a library of the hybrid molecules of pharmaceutical and medicinal interest and drug discovery research incorporating privileged heterocyclic substructure. This protocol has special features such as operation simplicity, high atom economy, shorter reaction time (10–20 min), mild reaction conditions and excellent yield (80–94%). The present synthetic methodology is advantageous for commercial uses due to the recyclability and reusability of the catalyst.

Graphical abstract