Abstract: The present invention relates to a process for the stereoselective preparation of a compound having the general formula (I) or its respective diastereomers: comprising reacting a compound having the general formula (II) or its diastereomers: with a compound of the general formula III: R3—COOH and a compound of the general formula IV: R4—NC wherein R1 represents each independently, or jointly a substituted or unsubstituted alkyl, alkenyl, alkynyl, aromatic or non-aromatic, mono-, di- or tricyclic, or heterocyclic structure, and R2 represents a hydrogen atom, a substituted or unsubstituted alkyl, alkenyl, alkynyl, aromatic or non-aromatic, mono-, di- or tricyclic, or heterocyclic structure, and R3 represents a substituted or unsubstituted alkyl, alkenyl, or alkynyl, or an aromatic or non-aromatic aromatic or non-aromatic, mono-, di- or tricyclic, or heterocyclic structure.