Although the synthesis and study of anion receptors has been the topic of intense investigation for over two decades, the notion that anion-binding can be of significance or even an essential design element for catalytic enantioselective processes was not realized until relatively recently.  Our group has advanced several approaches that utilize anion-recognition in distinct ways.  The combination of an achiral acyl pyridinium salt and a chiral anion receptor catalyst (e.g., a thiourea compound) provides the basis for asymmetric acyl-transfer processes that operate via discrete ion pairs.  This concept is applicable to the kinetic resolution of various classes of amines, the desymmetrization of <i>meso</i>-diamines, and other asymmetric acyl-transfer reactions.  A new class of asymmetric Brønsted acid catalysts was generated by covalently linking an anion receptor via an appropriate chiral spacer to an acidic site, typically a simple carboxylic acid.  Upon protonation of a substrate, the conjugate base interacts with the anion recognition site, resulting in the formation of a rigid substrate-catalyst ion pair.  This stabilization of the conjugate base renders simple carboxylic acids sufficiently acidic to promote a range of enantioselective transformations.  In this lecture, we will present our recent progress in this area.  Mechanistic insights into the nature of ion pairing and the impact of catalyst aggregation will be discussed.

Anion-recognition/ion-pairing approaches to asymmetric catalysis

251st National Meeting (2016)

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