Synthesis of Monospiro-2-amino-4H-pyran Derivatives Catalyzed by Propane-1-sulfonic Acid-Modified Magnetic Hydroxyapatite Nanoparticles

Various monospiro-2-amino-4H-pyran derivatives have been synthesized in high yields (via three-component coupling of ninhydrin or different isatins with malononitrile and 1,3-dicarbonyl compounds) in the presence of catalytic amount of propane-1-sulfonic acid-modified magnetic hydroxyapatite nanoparticles in H2O. Due to easy magnetic removal of nanocatalyst and applying of H2O as solvent, this protocol enhanced product purity, and promised economic as well as environmental benefits, exemplifying a waste-free chemistry. More importantly, the catalyst could be easily recycled for more than five times without loss of activity.