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 α,α-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 α,β-unsaturated aldehydes was evaluated. Respective (S) or (R) adducts were obtained in the reactions in high yields (up to 95 %) and with high enantioselectivity (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.