Chemo-, regio- and stereoselectivity in steroids hydrogenation with Cu/Al2O3. Intra- and intermolecular hydrogen transfer reactions

The hydrogen transfer from different secondary alcohols to a steroidic conjugated enone and a saturated ketone in the presence of Cu/A/2O3 has been investigated. The stereochemical pathway of the reaction has been studied and the results are compared with those obtained by conventional molecular hydrogen addition in the presence of the same catalyst. While chemo- and regioselectivity are essentially unaffected by the hydrogen source, the stereoselectivity of the hydrogen addition to the conjugated olefinic moiety depends upon the alcohol used as hydrogen donor, and 5?:5? isomer ratios ranging between 48 and 85% were observed. In the second step of H2 addition, the reduction of the 3-keto-group, a strong effect of the donor molecule on the stereochemistry was observed moving from 2-propanoi to 2-octanol. However, an excess of the equatorial alcohol was obtained in every case.