Assessment of the organocatalytic activity of chiral l-Proline-based Deep Eutectic Solvents based on their structural features

Abstract

The impact on the environment of polluting and volatile organic solvents represents nowadays a severe problem. In order to reduce the incidence on the environment of chemical applications, Deep Eutectic Solvents (DESs) represent a step ahead in this field thanks to their green properties. These novel liquids are formed by inter- and intra-molecular weak interactions between two species and they are synthesized by simply heating and mixing them without any solvent. These solvents also show interesting catalytic capabilities, since their properties are truly tuneable. In this paper, l-Proline-based Chiral Deep Eutectic Solvents (CDESs) were prepared and used as green and organocatalytic reaction media in a probe asymmetric Michael addition; in this reaction the l-Proline acts as solvent component as well as chiral organocatalyst. The results were analysed with NMR studies taking in account the availability of the l-Proline, considering the strength of the association of it with the counterpart of the liquids. With DFT studies, the geometry and energy of the adducts are shown and a qualitative rationale to the reaction stereoisomers distribution is given.