TOTAL SYNTHESIS WITH A CHIROGENIC OPENING MOVE DEMONSTRATED ON STEROIDS WITH ESTRANE OR 18A-HOMOESTRANE SKELETON

A concept of first choice for the synthesis of the title compounds had been proposed by Dane in the late 1930s. It was soon turned down, because the opening move - a chirogenic Diets-Alder reaction - did not work. With Lewis acids as mediators, however, a successful start has been achieved now. With Ti complexes of chelating ligands (Seebach's TADDOLs ( = alpha,alpha,alpha',alpha'-tetraaryl-1,3-dioxolane-4,5-dimethanols)) enantioselective formation of the desired adducts does occur. Efficient total syntheses of 2 and 3a have been accomplished.