BETA-ALKOXYALKYLPHOSPHANES AND BETA-HYDROXYALKYLPHOSPHANES AS LIGANDSIN THE STEREOSELECTIVE HYDROGENATION - A COMPARISON

Optically pure 1,4-bis(diphenylphosphanyl)-2-hydroxy-butane (2) and it s methyl ether 1 can be conveniently prepared by starting from chiral pool substances such as malic or L-ascorbic acid. Different pathways t o these compounds were elucidated. In one case an interesting migratio n of an acetalic OH-protective group was observed. The reaction of the bisphosphanes with Rh-I or Pd-II gave uniform metal complexes. On the basis of X-ray structural analysis, NMR and IR data it was concluded that in the investigated precatalysts of the type [Rh(COD)(bisphosphan e)]BF4 a coordination of the alkoxy or hydroxy oxygen to the metal doe s not take place. Nevertheless, significant differences in enantiosele ctivity and activity could be observed when several prochiral substrat es were hydrogenated.