Asymmetric ion-pairing catalysis
Asymmetric ion-pairing catalysis in chemistry is a type of asymmetric catalysis taking place specifically with charged intermediates or charged reagents. In one type of catalysis ion-pairing exists with a charged and chiral catalyst. The charged catalyst can be cationic or anionic. Catalysis by anionic catalysts is also called asymmetric counteranion-directed catalysis. In the other variation of asymmetric ion-pairing catalysis called anion or cation binding, the chiral catalyst is neutral but binds in a noncovalent way to an intermediate ion pair. Asymmetric ion-pairing catalysis is distinct from other covalent types of catalysis such as Lewis acid catalysis and Bronsted acid catalysis.[1] It is one of several strategies in enantioselective synthesis and of some relevance to academic research.
The first reported example of this type of catalysis is attributed to Dolling, Davis & Grabowski who in 1984 used a chiral cinchonidine based phase transfer catalyst in the synthesis of indacrinone.[2] Important chiral cation scaffolds are quaternary ammonium cations and quaternary phosphonium cations. The first reported example of asymmetric cation-binding catalysis originates from Cram and Sogah who in 1981 used a chiral crown ether in combination with a potassium base in an enantioselective Michael addition.[3] The development of chiral anionic catalysists is a more recent research field. In 2000 Llewellyn, Adamson & Arndtsen used a chiral borate anion in olefin aziridination and cyclopropanation.[4] Another regularly encountered scaffold is a chiral phosphate anion together with iminium, carbocationic or oxocarbenium counterions. Chiral anion phase-transfer catalysis was introduced by Toste in 2007. [5]
References
[edit]- ^ Brak, K. and Jacobsen, E. N. (2013), Asymmetric Ion-Pairing Catalysis. Angew. Chem. Int. Ed., 52: 534–561. doi:10.1002/anie.201205449
- ^ Efficient catalytic asymmetric alkylations. 1. Enantioselective synthesis of (+)-indacrinone via chiral phase-transfer catalysis Ulf H. Dolling, Paul Davis, and Edward J. J. Grabowski Journal of the American Chemical Society 1984 106 (2), 446-447 doi:10.1021/ja00314a045
- ^ Chiral crown complexes catalyse Michael addition reactions to give adducts in high optical yields Donald J. Cram and G. D. Y. Sogah J. Chem. Soc., Chem. Commun., 1981, 625-628 doi:10.1039/C39810000625
- ^ A Novel Example of Chiral Counteranion Induced Enantioselective Metal Catalysis: The Importance of Ion-Pairing in Copper-Catalyzed Olefin Aziridination and Cyclopropanation David B. Llewellyn,Dan Adamson, and, and Bruce A. Arndtsen Organic Letters 2000 2 (26), 4165-4168 doi:10.1021/ol000303y
- ^ Chiral Anion-Mediated Asymmetric Ring Opening of meso-Aziridinium and Episulfonium Ions Gregory L. Hamilton, Toshio Kanai, and F. Dean Toste Journal of the American Chemical Society 2008 130 (45), 14984-14986 doi:10.1021/ja806431d