Supramolecular Interactions Based on Ionic Liquids for Tuning of the Catalytic Efficiency of (L)-Proline

Abstract

Noncovalent intermolecular interactions between (l)-proline and ionic liquids (ILs) are key to explain the different catalytic efficiencies observed for this organocatalyst in the aldol reaction carried out in ILs or in the presence of ILs as cosolvents. The catalytic behavior of (l)-proline has been studied in reaction media containing nonchiral (e.g., [Bmim][Cl]) and chiral (e.g., [(R,R)-trans-Cy6-OAc-Im-Bu][Cl]) ILs using the synthesis of 4-hydroxy-4-(4-nitrophenyl)butan-2-one via the aldol reaction between p-nitrobenzaldehyde and acetone as a model reaction. The high degree of supramolecular organization induced by the presence of the ILs or chiral ILs (CILs) can contribute not only to enhance the activity, but also, in some cases, to tune the asymmetric induction.