Process for preparing protected, enantiomer-enriched cyanohydrins by in-situ derivatization

A process for preparing protected, enantiomer-enriched cyanohydrins of the formula ##STR1##

where R1 and R2 independently of one another can be an unsubstituted, monosubstituted or polysubstituted C₁-C₂₀-alkyl, C₅-C₂₀-aryl, C₅-C₂₀-heteroaryl, C₅-C₂₀-alkaryl, C₅-C₂₀-alkylheteroaryl or C₅-C₂₀-aralkyl radical or an unsubstituted, monosubstituted or polysubstituted C₅-C₂₀-heterocycle, or C₅-C₂₀-alkylheterocycle or together can be an unsubstituted or substituted C₄-C₂₀-alkylene radical, which can contain one or more heteroatoms in the chain, or one of the radicals is hydrogen, and R3 can be an unsubstituted or substituted C₁-C₂₀-alkyl, C₅-C₂₀-aryl or C₅-C₂₀-heteroaryl radical, by reacting an aldehyde or ketone of the formula ##STR2##

where R1 and R2 are defined as above, in the presence of an (R)- or (S)-hydroxynitrile lyase in an organic, aqueous or 2-phase system or in emulsion at a temperature of -;5 to +40 C. with a carbonic ester nitrile of the formula ##STR3##

where R3 is defined as above.