Amberlite-Supported L-Prolinate: A Novel Heterogeneous Organocatalyst for the Three-Component Synthesis of 4H-Pyrano[2,3-c]pyrazole Derivatives

This report describes a new and convenient procedure for heterogenization of L-proline organocatalyst, which 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 treatment of a MeOH/H2O solution of L-proline with amberlite IRA900OH at 60 degrees C. L-Proline anion was exchanged with hydroxide ion and immobilized via ionic interaction between the carboxylate group of L-prolinate and quaternary ammonium cation of the cationic amberlite support. The prepared heterogeneous organocatalyst was characterized by FTIR, TGA, DTG, XRD, and elemental analysis techniques. The amberlitesupported catalyst was used as an efficient, reusable, and cheap catalyst for the one-pot three-component synthesis of 4H-pyrano[2,3-c] pyrazole derivatives in ethanol. The catalyst can be easily recovered and reused by simple filtration for several successive runs with no significant loss of catalytic activity.