Process for the manufacturing of a compound of formula comprising the step of reacting a compound of formula (II-A) and a compound of formula (II-B) or a ketal thereof in the presence of an organic solvent and either of at least one chiral compound of formula (II-C) and of at least one Brønsted acid having a pK a of between 5 and 10.5, measured at 25°C in DMSO; or of at least one chiral compound of formula (II-C-A) having a pK a of between 5 and 10.5, measured at 25°C in DMSO, or an internal salt thereof wherein R 1, R 3 and R 4 are independently from each other hydrogen or methyl groups; R 2 and R 2' represents hydrogen or a phenol protection group; R 5 represents either a linear or branched completely saturated C 6-25 -alkyl group or a linear or branched C 6-25 -alkyl group comprising at least one carbon-carbon double bond; Y 1 represents either CH 2 Y 2 or wherein R 6 represents a linear or branched C 1-12 -alkyl group which optionally further comprises at least one aromatic group and/or C=O and/or NH and/or NH 2 group; Y 2 represents either OH or OR 7 or NHR 7 or NHCOOR 7 or wherein R 7 represents either a linear or branched C 1-12 -alkyl group which optionally further comprises at least one aromatic group and/or C=O and/or NH and/or NH 2 group or an aryl group or a substituted aryl group or a heteroaryl group or a substituted heteroaryl group and A represents a substituent carrying a Brønsted acid functional group and the dotted line(s) represents the bond(s) by which the corresponding substituent is bound to the rest of formula (II-C); and wherein * represents the chiral centre of the chiral isomer of formula. of at least one chiral compound of formula (II-C) and of at least one Brønsted acid having a pK a of between 5 and 10.5, measured at 25°C in DMSO; of at least one chiral compound of formula (II-C-A) having a pK a of between 5 and 10.5, measured at 25°C in DMSO, or an internal salt thereof wherein R 1, R 3 and R 4 are independently from each other hydrogen or methyl groups; R 2 and R 2' represents hydrogen or a phenol protection group; R 5 represents either a linear or branched completely saturated C 6-25 -alkyl group or a linear or branched C 6-25 -alkyl group comprising at least one carbon-carbon double bond; Y 1 represents either CH 2 Y 2 or wherein R 6 represents a linear or branched C 1-12 -alkyl group which optionally further comprises at least one aromatic group and/or C=O and/or NH and/or NH 2 group; Y 2 represents either OH or OR 7 or NHR 7 or NHCOOR 7 or wherein R 7 represents either a linear or branched C 1-12 -alkyl group which optionally further comprises at least one aromatic group and/or C=O and/or NH and/or NH 2 group or an aryl group or a substituted aryl group or a heteroaryl group or a substituted heteroaryl group and A represents a substituent carrying a Brønsted acid functional group and the dotted line(s) represents the bond(s) by which the corresponding substituent is bound to the rest of formula (II-C); and wherein * represents the chiral centre of the chiral isomer of formula. wherein R 1, R 3 and R 4 are independently from each other hydrogen or methyl groups; R 2 and R 2' represents hydrogen or a phenol protection group; R 5 represents either a linear or branched completely saturated C 6-25 -alkyl group or a linear or branched C 6-25 -alkyl group comprising at least one carbon-carbon double bond; Y 1 represents either CH 2 Y 2 or wherein R 6 represents a linear or branched C 1-12 -alkyl group which optionally further comprises at least one aromatic group and/or C=O and/or NH and/or NH 2 group; Y 2 represents either OH or OR 7 or NHR 7 or NHCOOR 7 or wherein R 7 represents either a linear or branched C 1-12 -alkyl group which optionally further comprises at least one aromatic group and/or C=O and/or NH and/or NH 2 group or an aryl group or a substituted aryl group or a heteroaryl group or a substituted heteroaryl group wherein R 6 represents a linear or branched C 1-12 -alkyl group which optionally further comprises at least one aromatic group and/or C=O and/or NH and/or NH 2 group; Y 2 represents either OH or OR 7 or NHR 7 or NHCOOR 7 or wherein R 7 represents either a linear or branched C 1-12 -alkyl group which optionally further comprises at least one aromatic group and/or C=O and/or NH and/or NH 2 group or an aryl group or a substituted aryl group or a heteroaryl group or a substituted heteroaryl group wherein R 7 represents either a linear or branched C 1-12 -alkyl group which optionally further comprises at least one aromatic group and/or C=O and/or NH and/or NH 2 group or an aryl group or a substituted aryl group or a heteroaryl group or a substituted heteroaryl group a linear or branched C 1-12 -alkyl group which optionally further comprises at least one aromatic group and/or C=O and/or NH and/or NH 2 group or an aryl group or a substituted aryl group or a heteroaryl group or a substituted heteroaryl group and A represents a substituent carrying a Brønsted acid functional group and the dotted line(s) represents the bond(s) by which the corresponding substituent is bound to the rest of formula (II-C); and wherein * represents the chiral centre of the chiral isomer of formula.