The ring-a aromatization of 11β-hydroxyl or 11β-methoxyl estra-4,9-diene derivatives was studied. It was found that these estradiene derivatives would give rise to estra-1,3,5-(10), 9(11)-tetraens when treated with acidic catalyst in protonic solvents. A estra-4,9,11-trene-3,17- dione intermediate mechanism was suggested and partly confirmed by further investigation. The aromatization process can also be catalyzed by Iodine.

Key words: ESTROGEN