Patent ID: 8546571

Claim:
A process for preparing the S or R enantiomer of a compound of formula A, the process comprising subjecting a compound of formula B to asymmetric hydrogenation in the presence of a chiral catalyst and a source of hydrogen wherein the chiral catalyst comprises a Ru-biphosphine metal complex, wherein: X is oxygen; R 1 , R 2 and R 3 are the same or different and signify hydrogens, halogens, alkyl, alkyloxy, hydroxy, nitro, alkylcarbonylamino, alkylamino or dialkylamino group; and R 4 is alkyl or aryl, wherein: the term alkyl means hydrocarbon chains, straight or branched, containing from one to six carbon atoms, optionally substituted by aryl, alkoxy, halogen, alkoxycarbonyl or hydroxycarbonyl groups; the term aryl means a phenyl or naphthyl group, optionally substituted by alkyloxy, halogen or nitro group; and the term halogen means fluorine, chlorine, bromine or iodine and wherein at least one of R 1 , R 2 and R 3 is fluorine.