| 摘要 |
The present invention is concerned with a novel process for the preparation of compounds of formula (I) comprising catalytic asymmetric hydrogenation of a compound of formula (II) in the presence of a catalyst comprising ruthenium and a chiral diphosphine ligand or comprising rhodium and a chiral diphosphine ligand, wherein R1, R2, R3 and R4 are as defined in the specification and claims. The compounds of formula (I) and the corresponding salts and/or esters are pharmaceutically active substances.
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