A method for the preparation of (S)-
alcohol oxazolidides of general formula II, in which PG represents
hydrogen or a hydroxyl
protecting group, such as
trimethylsilyl, tert-butyldimethylsilyl, benzyloxycarbonyl, tert-butoxycarbonyl, benzyl, benzhydryl or trityl, in which a ketal oxazolidide of general formula III, where PG has the same meaning as above and R means an
alkyl with 1-4 carbon atoms, linear or branched, such as methyl, ethyl,
isopropyl or butyl, or R+R together represents a
divalent alkyl, or substituted with 1 or 2
alkyl groups, e.g. 1,2-
ethylene, 1,2-propylene, 1,2-butylene, 1,3-propylene or 2,2-dimethyl-1,3-propylene, is deprotected by the action of acidic reagents in a mixture of water and a water-miscible
solvent in the temperature range of 0 to 100° C. (stage A), and the obtained
ketone oxazolidide of general IV, in which PG has the same meaning as above, is reduced with asymmetrical reagents in an
inert organic solvent in the temperature range of −30 to +40° C. (stage B).