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. (C) 2014 Elsevier Ltd. All rights reserved.