Asymmetric Aldol Reaction Catalyzed by the Anion of an Ionic Liquid

Herein we report the synthesis of a chiral imidazolium
salt derived
from trans-l-hydroxyproline and its applications
as a catalyst for the asymmetric aldol reaction. By performing the
aldol reaction in [Bmim]­NTf2 as a solvent, we report excellent
isolated yields of the aldol product (up to 99%), as well as modest
to excellent selectivities (dr superior to 99:1. ee up to 89%). Mechanistic
insights and the origins of the selectivity of the aldol reaction
are discussed on the basis of the results obtained with two catalytic
imidazolium salts having different H-bonding potential.