Homogeneous and heterogeneous catalytic asymmetric reactions: II. Asymmetric hydrogenation of steroid ketones

The asymmetric reduction of steroid 17- and 20-ketones with chiral hydrosilanerhodium-(+)- and (−)-diop-complex catalysts allows different stereoselectivities in the formation of 17-alchols, but not of 20-alcohols. The degree of this stereoselectivity is higher than that attained with other methods. The stereoselectivity can be explained in terms of the most preferred conformation of the α-siloxysteroid-rhodium intermediate complexes.