Asymmetric transfer hydrogenation of 2-aryl substituted bicyclic pyridine ketones in presence of a chiral ruthenium catalyst

A process for preparing a compound of formula (Ia) or (Ib),

• where
• R1 and R2 are independently from one another selected from the group consisting of hydrogen and C1-C4-alkyl,
• each R3, if present, is independently selected from C1-C4-alkyl, and
• n is 0, 1, 2 or 3,
• comprising asymmetric transfer hydrogenation of a ketone of formula (II)
• in which the substituents R1, R2, R3 and the integer n are as defined for the compound of formula (Ia) or (Ib),
• in presence of a chiral ruthenium catalyst and a polar solvent, wherein the ruthenium catalyst comprises a chiral amino alcohol ligand or a chiral diamine ligand.