Bifunctional Catalysts: Two for One

  • Author: Andrea Stomps
  • Published Date: 17 November 2016
  • Source / Publisher: Chemistry – A European Journal/Wiley-VCH
  • Copyright: Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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α-Hydroxy-β-dicarbonyl structures are often found in biologically active compounds such as pharmaceuticals. They can be synthesized through direct α-hydroxylation with either chiral auxiliaries or enantioselective catalysts.


Mario Waser, Johannes Kepler University, Linz, Austria, and colleagues, have used chiral urea-containing ammonium salts as bifunctional catalysts that not only catalyze the direct α-hydroxylation of β-ketoesters with oxaziridines under base-free conditions, but also enable the simultaneous kinetic resolution of these oxaziridines. Using this catalyst system, the researchers were able to obtain the desired α-hydroxy-β-dicarbonyl products in up to 97 % yield after two hours with enantiomeric ratios of up to 99:1. In addition to this, increasing the amount of oxaziridine in the reaction mixture resulted in significant enantioenrichment of the unreacted oxaziridine up to an enantiomeric ratio of 94:6.


The researchers also observed a pronounced dependence of the effectiveness of the reaction on the enantiomeric composition of catalyst and oxaziridine, with a considerably higher reactivity for the matched pairs (both S,S- or both R,R-configured). These bifunctional catalysts are a promising tool for asymmetric synthesis of biologically relevant compounds.


 

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Magazine of Chemistry Europe (16 European Chemical Societies) published by Wiley-VCH