Ionic liquids as green solvents for the asymmetric synthesis of cyanohydrins catalysed by VO(salen) complexes

Abstract

It has been found that the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate is a good substitute solvent for CH₂Cl₂ to conduct the enantioselective cyanosilylation of aldehydes to their silylated cyanohydrins, using trimethylsilyl cyanide as reagent and a Schiff base vanadyl complex as catalyst. The mass balances (>90%), conversions (>80%) and enantiomeric excess (88% < ee < 90%) were high and comparable to those achieved in CH₂Cl₂. The ionic liquid containing the catalyst can be reused at least four times without loosing activity.