Oxygenation of 2, 4-Dibromoestrogens with Nitric Acid : A New Synthesis of 19-Nor Steroids

Abstract

A convenient synthesis of 19-nor steroids 4a, 4b, 12a, and 12c is described. Oxygenation of 2, 4-dibromoestrogens 1a, 1b, 8a, and 8b with nitric acid in acetic acid gave the corresponding 2, 4-dibromo-10β-hydroxy-1, 4-dien-3-one derivatives 2a, 2c, 9a, and 9d in excellent yields. These 10β-hydroxy-dienones were subjected to catalytic hydrogenation over palladium-on-charcoal to afford the saturated 5ξ-3-oxo derivatives 3a, 3b, 10a, and 10b, respectively, in very high yields. These saturated products were then converted into the corresponding 19-nor steroids 4a, 4b, 12a, and 12c by treatment with acid, perchloric acid, p-toluenesulfonic acid or Nafion-H.