Process for the preparation of enantiomerically pure (S)- or (R)-4-halo-3-hydroxybutyrates of formula
wherein R1 is CH2X, CHX2 or CX3 and X independently represents Cl and/or Br and wherein R2 is C1-6-alkyl, C3-8-cycloalkyl, aryl or aralkyl, each aryl or aralkyl being optionally further substituted with one or more C1-4-alkyl groups and/or halogen atoms, by asymmetric hydrogenation of 4-halo-3-oxobutyric acid esters of formula
wherein R1, R2 and X are as defined above
in the presence of a catalyst of a ruthenium complex comprising a chiral ligand of the formula
制备(S)-或(R)-4-卤代-3-羟基
丁酸酯的过程,其中公式中的R1为CH2X、CHX2或CX3,X独立表示Cl和/或Br,R2为C1-6-烷基、C3-8-环烷基、芳基或芳基烷基,每个芳基或芳基烷基可以进一步取代一个或多个C1-4-烷基基团和/或卤素原子,通过不对称氢化4-卤代-
3-氧代丁酸酯的过程制备,其中公式中的R1、R2和X如上定义,在含有手性
配体的
钌配合物催化剂的存在下。该手性
配体的公式为: