Chiral Ionic Liquids Bearing O-Silylated α,α-Diphenyl (S)- or (R)-Prolinol Units: Recoverable Organocatalysts for Asymmetric Michael Addition of Nitroalkanes to α,β-Enals

Chiral ionic liquids bearing O-silylated alpha,alpha-diphenyl (S)- or (R)-prolinol units tagged to the imidazolium cation were synthesized and their activity as catalysts in the Michael addition of nitroalkanes to alpha,beta-unsaturated aldehydes was evaluated. Respective (S) or (R) adducts were obtained in the reactions in high yields (up to 95%) and with high enantio-selectivity (up to 99% ee). Remarkably, the immobilized organocatalysts could be used five times without any decrease in product yields or ee values. (R)-Michael adducts could be easily transformed into the most active (R) enantiomers of medications Phenibut, Baclofen, and Rolipram for the treatment of CNS disorders.