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.