Silica sulfuric acid magnetic nanoparticles efficiently catalyze the one-pot, three-component reaction of isatins and malononitrile with dimedone, 1,3-dimethylbarbituric acid or 4-hydroxycoumarin in EtOH-H2O to afford the corresponding spiro[2-amino-4H-pyran-oxindole] derivatives in high yields under ultrasound irradiation at 60 °C. The heterogeneous nanocatalyst could be recovered easily from the reaction mixture using an external magnet and reused many times without significant loss of its catalytic activity.
