5 /J,6/?-Epoxidation of 3 jß-Cholesteryl Acetate and its Analogues

The incorporation of oxygen containing groups into the steroid structure is of considerable interest in connection with the synthesis of corticosteroids and cardioactive substances. Oxidations with reagents containing hexavalent chromium have been widely used either to functionalize non-activated positions of policyclic hydro­ carbons [1 ], or to obtain through allylic oxidations keto derivatives from unsaturated hydrocarbons [2, 3], Treatment of olefins with oxidative reagents such as chromyl chloride [4], chromic acid [5] and chromyl acetate [6 ] yields a variety of complex mixtures. Evi­ dence of epoxide formation as intermediates in such oxidations has been reported [7, 8 ], as well as epoxi­ dation of allylic alcohols with chromium trioxide [9]. The latter reaction failed when the hydroxyl group was acetylated. We wish to report a stereoselective 5/3,6/3-epoxidation on zT-steroids using chromyl diacetate under specific conditions (see below). Previous approaches to /3-epoxide formation involved the preparation of rra/js-halohydrins followed by treatment with base [ 1 0 ], treatment of an olefin with organic peracids [ 1 1 ] followed by separation of the isomeric epoxides, or treatment of an unsaturated steroid with hydrogen peroxide in acetonitrile containing ferric acetylacetonate [1 2 ].