Synthesis and Application of L-Proline Taurinate as a Novel Bifunctional Ionic Catalyst for the Highly Efficient Synthesis of 2-Amino-3-Cyano-4H-Pyrans and Pyran-Annulated Heterocycles

Abstract

This research introduces a groundbreaking bifunctional ionic catalyst, L-proline taurinate, synthesized in water using biodegradable materials, aligning with green chemistry principles. The structure of the synthesized catalyst was characterized using FT-IR, ¹H NMR, ¹³C NMR, and HRMS. The ionic nature of the catalyst was validated through density functional theory analysis. The catalyst demonstrated exceptional efficiency in the green synthesis of 2-amino-3-cyano-4H-pyrans and pyran-annulated heterocyclic scaffolds. A total of 23 compounds were synthesized in less than 10 min with excellent yields (86–98%), through the Knoevenagel-Michael-cyclization coupling reaction of aldehydes, 1,3-diketones, and malononitrile. The substrate versatility was demonstrated with substituted aromatic and heterocyclic aldehydes, along with 1,3-dicarbonyl compounds like dimedone, 1,3-cyclohexanedione, and 4-hydroxy-2H-chromen-2-one, as well as barbituric acid, 2-thiobarbituric acid, and 3-methyl-1-phenyl-2-pyrazoline-5-one. This robust protocol boasts features such as one-pot, single-step, three-component operations, easy catalyst separation and recycling potential, broad applicability to various substrates, and suitability for gram-scale production. This innovative approach represents a major stride in sustainable catalytic technology and green chemical procedures, paving the way for future advancements in eco-friendly synthesis techniques.

Graphical Abstract