Magnetite L-proline as a reusable nano-biocatalyst for efficient synthesis of 4H-benzo[b]pyrans in water: a green protocol

L-Proline is known as the most favored organocatalyst in enamine-mediated reactions. The unique nucleophilic character of L-proline among other amino acids raised from the secondary amine functionality in its pyrrolidine ring. This simple natural amino acid as a promising catalyst for various kinds of organic reactions can compete with the toxic organometallic catalysts. Magnetic functionalization of this organocatalyst could solve its recovery and reuse problems. Herein we report the use of magnetic L-proline nano-biocatalyst for a simple and efficient one-pot coupling reaction of dimedone, malononitrile and aromatic aldehydes to afford the corresponding tetrahydrobenzo[b]pyrans as a significant class of heterocyclic compounds with great biological and pharmacological importance according to a green protocol. Low cost, facile handling, simple preparation, high stability, reusability and low toxicity of this nano-biocatalyst besides its high efficiency and versatility proposed it as a unique candidate for many of enamine-mediated organic transformations