Development of L-Proline-Based Chiral Ionic Liquids for Asymmetric Michael Reaction
Karolina Zalewska, Isabel S.S. Pinto, Luís Cabrita, Małgorzata E. Zakrzewska, João Paulo Noronha, Manuel Nunes da Ponte, Luı́s C. Branco
Abstract
Different Chiral Ionic Liquids (CIL) based on L-proline have been developed. Simple and efficient synthetic methodologies are used, allowing preparation in good yields for twelve novel CILs using L-proline as a cation or anion combined with suitable counter-ions. A detailed physical and chemical characterization of the CILs was performed to evaluate the influence of counter-ions on the final properties. The most promissory CILs were tested as efficient chiral catalysts in IL media for asymmetric Michael addition reactions of ketones and aldehydes to nitro-olefins. Similar or even better conversions and enantioselectivities (ee up to 95%) compared to the original L-proline were achieved. Additionally, a good product extraction performance using supercritical CO2 processes was obtained.