Deep Eutectic Solvents formed by chiral components as chiral reaction media and studies of their structural properties

Abstract

We present the realization, the use as reaction media/chiral organocatalysts/acid catalysts and the structural properties of novel chiral Deep Eutectic Solvents. These liquids are formed by mixtures of chiral HBD and HBA molecules that are common, relatively cheap and commercially available (the two enantiomers of camphorsulfonic acid as HBD) or easily one-step synthesized molecules from commercially available compounds ((S)- and (R)-N,N,N-trimethyl-(1-phenylethyl)ammonium methanesulfonate as HBA). These liquids proved to be highly-structured as showed by different yields and enantiomeric excesses observed in a probe reaction, suggesting these liquids to form diastereoisomerically different liquids by changing one of the two enantiomers. Their structural features were analyzed via 1H Pulsed Field gradient Spin Echo (PGSE) NMR, NMR titration, 1H NMR analyses of formation and differences in the chemical shifts of the peaks of the liquids. Density Functional Theory (DFT) optimization helped to define the structures of these liquids. The methanesulfonate counterion of HBA molecule showed to be relevant in order to obtain these highly-structured liquids as it interacts specifically with the HBD. These chiral Deep Eutectic Solvents revealed to be promising novel high-structured media for enantioselective reactions.