Asymmetric Michael Addition Mediated by Chiral Ionic Liquids

Abstract

Chiral ionic liquids with a focus on their applications in asymmetric Michael additions and related reactions were reviewed. The examples were classified on the basis of the mode of asymmetric induction (e.g., external induction/non-covalent interaction or internal induction/covalent bond formation), the roles in reactions (as a solvent or catalyst), and their structural features (e.g., imidazolium-based chiral cations, other chiral oniums; proline derivatives). Most of the reactions with high chiral induction are Michael addition of ketones or aldehydes to chalcones or nitrostyrenes where proline-derived chiral ionic liquids catalyze the reaction through enamine/ iminium formation. Many reports demonstrate the recyclability of ionic liquid-tagged pyrrolidines.

Keywords: Chiral ionic liquid; Michael addition; asymmetric reaction; catalysts; chiral solvent; imidazole ionic liquid.

Fig. (1)

Imidazole ionic liquid from Chiral bicyclo[3.3.1]nonane-2,6-dione.

Fig. (2)

Various Michael addition products produced in the presence of 19a and 19b.

Fig. (3)

Proposed transition state for the reaction between cyclohexanones and nitroolefins.

Fig. (4)

Other imidazole ionic liquids bearing a 2-pyrrolidinylmethyl group.

Fig. (5)

Imidazole ionic liquids tehtered to a pyrrolidinylmethyltriazole moiety.

Fig. (6)

Imidazole ionic liquids bearing a n-(pyrrolidin-2ylmethyl)sulfonamide moiety.

Fig. (7)

Mechanism for Michael addition in the presence of imidazole ionic liquid bearing a N-(pyrrolidin-2ylmethyl)sulfonamide moiety.

Fig. (8)

Imidazole ionic liquid bearing a (N-(pyrrolidin-2ylmethyl)sulfamoyl)benzyl Group.

Fig. (9)

Ionic liquids tethered to a prolinol moiety.

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