Recyclable copper catalysts based on imidazolium-tagged bis(oxazolines): A marked enhancement in rate and enantioselectivity for Diels-Alder reactions in ionic liquid

Simon Doherty, Peter Goodrich, Christopher Hardacre, Julian G. Knight, Mimi T. Nguyen, Vasile I. Pârvulescu, Cristina Paun

    Research output: Contribution to journalArticlepeer-review

    Abstract

    Imidazolium-tagged bis(oxazolines) have been prepared and used as chiral ligands in the copper(II)-catalysed Diels-Alder reaction of N-acryloyland N-crotonoyloxazolidinones with cyclopentadiene and 1,3-cyclohexadiene in the ionic liquid 1-ethyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide, [emim] [NTf2]. A significant and substantial enhancement in the rate and enantioselectivity was achieved in [emim] [NTf2] compared with dichloromethane. For example, complete conversion and enantioselectivities up to 95 % were obtained for the reaction between N-acryloyloxazolidinone and cyclopentadiene within 2 min in [emim] [NTf2] whereas the corresponding reaction in dichloromethane required 60 min to reach completion and gave an ee of only 16%. The enhanced rates obtained in the ionic liquid enabled a catalyst loading as low as 0.5 mol % to give complete conversion within 2 min while retaining the same level of enantioselectivity. The imidazolium-tagged catalysts can be recycled ten times without any loss in activity or enantioselectivity and showed much higher affinity for the ionic liquid phase during the recycle procedure than the analogous uncharged ligand.

    Original languageEnglish
    Pages (from-to)951-963
    Number of pages13
    JournalAdvanced synthesis & catalysis
    Volume349
    Issue number6
    DOIs
    Publication statusPublished - Apr 2007

    Keywords

    • Asymmetric Diels-Alder reaction
    • Ionic liquids
    • Rate and enantioselectivity enhancements
    • Recyclability
    • Task-specific ionic liquids

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