ZrO2 nanoparticles as a reusable solid dual acid-base catalyst for facile one-pot synthesis of multi-functionalized spirooxindole derivatives under solvent free condition

A two-step one-pot protocol for the facile synthesis of biologically important spirooxindole derivatives such as spiro[4H-pyran-3,3'-oxindoles] and spiro[indoline-3,4'(1H')-pyrano-[2,3-c]pyrazol-2-ones has been developed. In this method ZrO2 nanoparticles have been utilized as a reusable solid dual acid-base catalyst to get quick access to the multi-functionalized spirooxindole derivatives under solvent free condition at room temperature. The main advantages of this method are the operational simplicity, reduced reaction time, elimination of solvents, high yield of the products, convenient work up procedure and employment of nontoxic and recyclable ZrO2 nano catalyst. All these factors make the present method economical, green and sustainable.