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DOI: 10.1055/s-2007-992440
Desymmetrization of Cyclohexanones Catalyzed by Chiral Ionic Liquids
Contributor(s):Benjamin List, Daniela KampenInstitute of Chemistry, Chinese Academy of Sciences, Beijing and Nankai University, Tianjin, P. R. of China
Functionalized Chiral Ionic Liquid Catalyzed Enantioselective Desymmetrizations of Prochiral Ketones via Asymmetric Michael Addition Reaction
J. Org. Chem. 2007, 72: 9350-9352
Publication History
Publication Date:
23 January 2008 (online)
Key words
desymmetrization - Michael addition - chiral ionic liquids - enamine catalysis
Significance
An organocatalytic desymmetrization of 4-substituted cyclohexanones (1) via Michael addition to nitroolefins (2) has been developed. Ketones 1 react with aromatic nitroalkenes 2 in the presence of chiral ionic liquid 3 (15 mol%) and salicylic acid (5 mol%) to give adducts of type 4 in high yields, diastereoselectivities and enantioselectivities. This transformation presumably proceeds via an enamine intermediate. A transition state illustrating the mode of face shielding by the imidazolium moiety to explain the observed relative and absolute configuration is proposed.
Comment
Inspired by the great success of proline and its derivatives in asymmetric organocatalysis, the authors have previously introduced the pyrrolidine backbone into the imidazolium unit of common ionic liquids resulting in a new class of highly efficient catalysts for the Michael addition of carbonyl compounds to nitroolefins (Angew. Chem. Int. Ed. 2006, 45, 3093). Now, they have extended this method to the use of ketones 1, which leads to the formation of more complex γ-nitroketones (4) bearing three stereocenters. Furthermore, chiral ionic liquids can be synthesized in a few steps and recycled after use.