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

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

• 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, which process comprises reacting an aldehyde or ketone of the formula
• 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 of substantially water-immiscible diluent and water or in emulsion at a temperature of −5 to +40° C. with a carbonic ester nitrile of the formula
• where R3 is defined as above,
• to give the corresponding O-protected, enantiomer-enriched cyanohydrins of the formula (I).