Imidazolium Sulfonates as Environmental-Friendly Catalytic Systems for the Synthesis of Biologically Active 2-Amino-4H-chromenes: Mechanistic Insights

J Phys Chem B. 2015 Sep 10;119(36):12042-9. doi: 10.1021/acs.jpcb.5b06275. Epub 2015 Aug 31.

Abstract

Ionic Liquids (ILs) are valuable reaction media extremely useful in industrial sustainable organic synthesis. We describe here the study on the multicomponent reaction (MCR) between salicylaldehyde (2) and ethyl cyanoacetate (3), catalyzed by imidazolium sulfonates, to form chromenes 1, a class of heterocyclic scaffolds exhibiting relevant biological activity. We have clarified the reaction mechanism by combining the experimental results with computational studies. The results reported herein suggest that both the imidazolium core and the sulfonate anions in the selected ILs are involved in the reaction course acting as hydrogen bond donors and acceptors, respectively. Contrarily to the most widely accepted mechanism through initial Knoevenagel condensation, the most favorable reaction pathway consists of an aldolic reaction between reagents followed by heterocyclization, subsequent dehydration, and, finally, the Michael addition of the second molecule of ethyl cyanoacetate (3) to yield the chromenes 1.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acetates / chemistry
  • Aldehydes / chemistry
  • Benzopyrans / chemical synthesis*
  • Benzopyrans / chemistry*
  • Catalysis
  • Chemistry Techniques, Synthetic
  • Green Chemistry Technology*
  • Imidazoles / chemistry*
  • Ionic Liquids / chemistry
  • Models, Molecular
  • Molecular Conformation
  • Sulfonic Acids / chemistry*

Substances

  • Acetates
  • Aldehydes
  • Benzopyrans
  • Imidazoles
  • Ionic Liquids
  • Sulfonic Acids
  • salicylaldehyde
  • ethyl cyanoacetate