Stereocontrolled catalytic hydrogenations of 3-oxocholestanes and some related compounds to the corresponding axial 3-alcohols

Abstract

Catalytic hydrogenations of 5α-cholestan-3-ones and related compounds with Urushibara nickel A catalyst in cyclohexane gave a distinct preponderance of unstable axial 3α-ols. Product ratios of axial alcohols decreased with increasing solvent polarity. For 3-oxo-5α-steroids, the cobalt catalyst was less selective for the axial alcohol formation. On the other hand, conversion of 5β-cholestan-3-one into the corresponding axial 3β-ol was most successfully attained by hydrogenation catalyzed by Urushibara cobalt A catalyst in methanol. For such a 5β-ketone, alcoholic media with higher polarities were more favorable for giving the product rich in axial alcohol. The stereochemistry of the products obtained from hydrogenations conducted in nonpolar solvents may be understood in terms of the steric congestion around the ketone carbonyl group. However, when alcohols were used as solvents, the product ratios obtained did not correlate well with the congestion ratios of substrates.