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Organocatalyzed synthesis of optically active cyanohydrins starting from alpha-ketoesters
1  Departamento de Química Orgánica, Universidad de Sevilla,


Optically active cyanohydrins are valuable building blocks in organic synthesis, as they can be converted in several interesting compounds as β-aminoalcohols, α-hydroxyacids or α-hydroxyketones. Different methodologies have been developed in order to obtain these compounds with high yields and optical purities, including organocatalysed reactions. The use of small organic molecules as catalysts has emerged as an useful tool for the preparation of chiral compounds, being employed different organocatalysts in the asymmetric synthesis of cyanohydrins.
The enantioselective cyanosilylation of a set of prochiral α-ketoesters with trimethylsilyl cyanide employing different chiral hydrogen bond catalysts has been performed. We have mainly focused in the use of  bifunctional thioureas containing a tertiary amine or a quaternary ammonium moiety in their structure. The parameters that can affect to the reaction activity and selectivty (solvent, cyanide source and its concentration, temperature and additives), have been studied and optimised in order to obtain the final products with the highest yields and selectivities. Thus, it is possible to obtain the highly functionalized chiral cyanohydrins in good yields and moderate enantiomeric excesses by working in toluene at -45ºC and employing cinchona based (thio)ureas.

Keywords: Organocatalysis; Cyanohydrins; Thioureas; Cinchona