Uncapped SnO₂ quantum dot catalyzed cascade assembling of four components: A rapid and green approach to the pyrano[2,3-c]pyrazole and spiro-2-oxindole derivatives

A new uncapped SnO₂ quantum dots (QDs) catalyzed strategy for the synthesis of substituted pyrano[2,3-c]pyrazole and spiro-2-oxindole derivatives has been developed via a multicomponent one pot approach in aqueous medium. The reactions can be performed at low catalyst loadings with excellent functional group tolerance. This communication also reports a comparative study of the efficiency related to the catalytic activity of uncapped SnO₂ QDs, oleic acid capped SnO₂ QDs, and SnO₂ nanoflower. Uncapped SnO₂ QDs, capped SnO₂ QDs, and SnO₂ nanoflower were prepared by simple solvothermal method and characterized by XRD, FESEM, and TEM images. The easy recovery of the catalyst and high yield of the products make the protocol attractive, sustainable, and economic. The catalyst was reused for six cycles with almost unaltered catalytic activity.