Ion-pair immobilization of l-prolinate anion onto cationic polymer support and a study of its catalytic activity for one-pot synthesis of spiroindolones

A novel clean and simple technique for the heterogenization of l-proline organocatalyst has been introduced. This procedure is based on non-covalent immobilization of l-proline on the surface of anion-exchange resin amberlite IRA900OH (AmbIRA900OH) as an efficient, cheap and commercially accessible cationic polymer support. The ion-pair immobilization of l-proline on the surface of amberlite IRA900OH was achieved by the treatment of a MeOH/H2O solution of l-proline with amberlite IRA900OH at 60 °C. l-Proline anion was exchanged with hydroxyl anion and immobilized via ionic interaction between carboxylate group of l-prolinate and quaternary ammonium cation of the cationic amberlite support. The prepared heterogeneous organocatalyst was well characterized using FTIR, TGA, DTG, XRD and elemental analysis techniques. This heterogeneous catalyst was used as an efficient recoverable catalyst for the synthesis of spiroindolone derivatives and good-to-excellent yields were obtained. The efficiency of the catalyst was almost completely maintained after 5 runs and very low leaching amount of organocatalyst into the reaction mixture occurred.