Steroids catalysts, iridium complexes

By a suitable choice of conditions (metal hydrides or metal/ammonia) ketones at the 1-, 2-, 4-, 6-, 7-, 11-, 12- and 20-positions in 5a-H steroids can be reduced to give each of the possible epimeric alcohols in reasonable yield. Hov/ever, the 3- and 17-ketones are normally reduced to give predominantly their -(equatorial) alcohols. Use of an iridium complex as catalyst leads to a high yield of 3a-alcohol, but the 17a-ol still remains elusive by direct reduction. 

---