Ion-pair immobilization of l-prolinate anion onto cationic polymer support and a study of its catalytic activity as an efficient heterogeneous catalyst for the synthesis of 2-amino-4H-chromene derivatives

Abstract

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 an 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 AmbIRA900OH was achieved by the treatment of a MeOH/H2O solution of l-proline with AmbIRA900OH at 60 °C. l-Proline anions were exchanged with hydroxyl anions and immobilized via ionic interaction between a carboxylate group of l-prolinate and quaternary ammonium cations of the cationic amberlite support. The prepared heterogeneous organocatalyst was well characterized by using FTIR, TGA, DTG, XRD, and elemental analysis techniques. The prepared heterogeneous organocatalyst was used as a catalyst for the one-pot, three-component synthesis of 2-amino-4H-chromene derivatives in EtOH at 80 °C. The reactions were efficiently performed in the presence of the title catalyst with short reaction times and gave the desired products at high yields. This catalyst can be straightforwardly recovered by simple filtration and recycled up to eight consecutive runs. Very low leaching of then organocatalyst into the reaction mixture occurred.