HOMOGENEOUS AND HETEROGENEOUS ASYMMETRIC REACTIONS - PART IX - ASYMMETRIC TRANSFER HYDROGENATION OF 16-METHYL-SUBSTITUTED STEROID 17-KETONES IN THE PRESENCE OF RHODIUM(I) COMPLEXES

Chiral transfer hydrogenation of 16 methyl-substituted steroid 17-keto nes in the presence of rhodium(I) complexes by hydrosilylation is desc ribed. During the preparation of the complex catalysts a wide variety of bidentate phosphines were used including chiral ligands, as well. T he diastereoselectivity of the reduction depends strongly on the struc ture of the ligands. The method applied produces the hydroxy steroid p roducts with excellent yield under very mild reaction conditions. Addi tionally, the procedure makes possible the preparation of 17 alpha-OH isomers beside the easily synthesizable 17 beta-OH products.