An efficient synthesis of amalgamated spiro heterocycles catalyzed by acid-functionalized Bi-doped CeO2 nanoparticles

Abstract

The present work presents the design and synthesis of bismuth-doped cerium oxide nanoparticles, followed by functionalization with sulfonic acid to introduce acidic sites on the surface. CeO₂:Bi@SO₃H was employed as an effective heterogeneous catalyst for the synthesis of spiro[imidazolidine−2,11′-indeno[1,2-b]quinoxalin]− 5-one derivatives. The spirocyclic hybrids were prepared through a one-pot multicomponent reaction under ultrasonic irradiation. This novel procedure generates an imidazole ring linked to indeno[1,2-b]quinoxaline via a spirocarbon, achieving yields ranging from good to excellent. The synthesis of the catalyst and spiroheterocycles was achieved using sustainable energy resources, leaving no hazardous residues. In the presence of the catalyst, a decrease in reaction time and an increase in product yield were observed, along with recyclability and reusability (up to 5 runs). Furthermore, the structure of the synthesized heterocycles was corroborated by FT-IR, ¹H NMR, ¹³C NMR, mass, and elemental composition. The catalyst was also characterized through various techniques, viz. energy-dispersive X-ray (EDX), field-emission scanning electron microscopy (FESEM), powder X-ray diffraction (XRD), BET surface area analysis, and Fourier transform infrared (FT-IR) spectroscopy.

Graphical abstract

A sustainable and effective multicomponent synthesis of spiroheterocycles has been accomplished using the recyclable CeO₂:Bi@SO₃H nanocatalyst.