| 摘要 |
The present invention provides a novel process for making compounds of formula (2a or 2b) or pharmaceutically acceptable salts thereof, wherein R1 is selected from the group consisting of phenyl and phenyl substituted with at least one group selected from NO2 and halogen, R2 is H; R3 is selected from the group consisting of C1-4 alkyl, phenyl, and benzyl; and, R4 is selected from the group consisting of H and halogen; which comprises the steps of: a) oxidizing a racemate of formula (2) or a salt thereof to form a dehydro-compound of formula (3), wherein R5 is selected from the group consisting of H, CH3, benzyl, C2-8 acyl, Na, Li and K; and, b) asymmetrically hydrogenating a compound of formula (3) in the presence of a chiral phosphine catalyst to form a compound of formula (2a or 2b).
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