14-Methyl steroids. Part 2. Total synthesis of (±)-14α-methyl-19-norsteroids

Abstract

trans-1,6-Dimethylbicyclo[4.3.0]nonane-2,7-dione (1) is converted, via regiospecific homologation at C-2, into trans-1,6-dimethyl-2-methylenebicyclo[4.3.0]nonane-3,7-dione (6). Conjugate alkylation of (6) with m-methoxybenzylmagnesium chloride followed by acid treatment, affords a mixture of (±)-3-methoxy-14-methyl-14α-estra-1,3,5(10),9(11)-tetraen-17-one (8) and the corresponding Δ⁸-isomer (9). The stereoselectivity of reductions of the Δ⁹⁽¹¹⁾- and Δ⁸-bonds in (8) and (9) and the derived 17-acetals is examined, and an efficient synthesis of (±)-3-methoxy-14-methyl-14α-estra-1,3,5(10)-trien-17-one (13) is described.