Ionic Liquid Gels: Supramolecular Reaction Media for the Alcoholysis of Anhydrides

Abstract

The search of new enantioselective catalysts, able to promote synthetically useful organic reactions with high levels of asymmetric induction, should be associated with the attention to the suitable reaction medium able to achieve the best efficiency in chemical processes. We have investigated the enantioselective desymmetrization of cyclic meso-anhydrides in nonconventional reaction media such as ionic liquids and supramolecular gels. With this aim, we examined several variables in the reacting system: the nature of ionic liquid used as the reaction medium, the gelation solvent, the structure of the anhydrides, the structure of alcohols, the chiral catalysts, and the reaction conditions, i.e., temperature and time. The different components of the system differently influence the reaction outcome, and to understand the interactions existing among them, 1 H NMR investigation was carried out. In general, the nonconventional reaction media demonstrated better performance than conventional ones, applying only a small amount of solvent. Good results in terms of yield and enantiomeric excess have been obtained in ionic liquid gels that seem promising media in the catalytic field. Furthermore, to the best of our knowledge, this is one of the first examples for the study of asymmetric alcoholysis of anhydrides in ionic liquid solution and gel phase.