STEREOCHEMISTRY OF THE HYDROGENATION OF 5α- AND 5β-CHOLESTAN-3-ONES OVER PLATINUM METALS. AN UNUSUAL ASPECT WITH PALLADIUM AND PLATINUM

Hydrogenation of 5α-cholestan-3-one with palladium gives an equatorial 3β-o1 while hydrogenation of 5β-cholestan-3-one under the same condition affords an axial 3β-o1 with high stereoselectivities in alcohols and tetrahydrofuran. This unusual hydrogenation stereochemistry is also seen with platinum in alcohols, but not with platinum in tetrahydrofuran nor with ruthenium, osmium and iridium in t-butyl alcohol. With rhodium in ethanol, the both ketones afford the axial alcohols in high selectivities.