Preparation of asymmetrically substituted biaryldiphosphines as ligands for enantioselective hydrogenation

Provided is a process for prepn. of asym. substituted biaryldiphosphine ligands I (R1 = C1-6-alkyl, C3-10-cycloalkyl optionally substituted with one or more halogen atoms; R2, R3 = aryl, C5-10-cycloalkyl, C1-6-alkyl, or R2 = C5-10-cycloalkyl, C1-6-alkyl; R3 = aryl optionally substituted with one or more substituents selected from the group consisting of halo, nitro, amino, C1-6-alkyl, C1-6-alkoxy, and di-C1-6-alkylamino groups, and each C1-6-alkyl, C5-10-cycloalkyl, C1-6-alkoxy and di-C1-6-alkylamino group in R2 and R3 optionally being substituted with one or more halogen atoms, from 2,2',6,6'-tetrabromobiphenyl) by a sequence of bromine metal exchanges and subsequent reactions. Thus, phosphination of 2,6,6-tribromo-2'-methoxy-1,1'-biphenyl (prepn. given) with Ph2PCl followed by isomerization gave 2',6-bis(diphenylphosphinyl)-2-methoxy-1,1'-biphenyl (ligand 1); RuCl3/(+)-ligand 1-catalyzed hydrogenation of Et acetoacetate in EtOH at 50 Deg gave (S)-Et 3-hydroxybutyrate in 6h. [on SciFinder (R)]