Synthesis of mono- and bis-spiro-2-amino-4H-pyrans catalyzed by S-alkyl O-hydrogen sulfothioate functionalized silica-coated magnetic nanoparticles under ultrasound irradiation

New S-alkyl O-hydrogen sulfothioate functionalized silica-coated magnetic nanoparticles were prepared in a simple method and evaluated as an efficient catalyst in synthesis of mono- and bis-spiro-2-amino-4H-pyrans through three or pseudo-five component reaction of isatins or bis-isatins and malononitrile with dimedone or 4-hydroxycoumarin. The yields were excellent, and the catalyst could be recovered simply from the reaction mixture using an external magnet and reused at least five times without noticeable loss of catalytic activity.