Chiral Ionic Liquids Based on l-Cysteine Derivatives for Asymmetric Aldol Reaction

Structure, and consequently properties, of ionic liquids can be easily tailored by changing cation/anion combinations and/or attaching functional groups. By grafting enantiopure moieties to the framework of ionic liquid it is possible to prepare bioinspired chiral molecules that can serve as a reaction medium, additive or even asymmetric catalyst. In this context, new chiral ionic liquids (CILs), based on biomolecules, such as aminoacids (l-Cysteine derivatives), have been synthesised and tested in asymmetric aldol condensation of aldehydes and ketones. The best results were obtained for CILs composed of S-methyl-l-cysteine cation and bis(trifluoromethane)sulfonimide anion, in the reaction of 2- or 4-nitrobenzaldehyde with acetone or cyclohexanone, giving the aldol product in moderate yields 70-76% and high ee values (up to 96%).

Automated summary

Ionic liquids' structures and properties can be tailored by changing cation/anion combinations or grafting enantiopure moieties, creating bioinspired chiral molecules for various applications. Chiral ionic liquids (CILs) based on biomolecules like amino acids have been synthesized and tested, showing promising results in asymmetric aldol condensation reactions with high yields and enantioselectivity.