ACID-MEDIATED REARRANGEMENTS OF 14,17-ETHENOESTRA-1,3,5(10)-TRIEN-17-OLS - SYNTHESIS OF 14,16-ETHANO-19-NORSTEROIDS

3-Methoxy-17(1)-methyl-14,17alpha-ethenoestra-1,3,5(10)-trien-17beta-ol 1 undergoes a 16(17-->17(1))abeo-rearrangement in the presence of boron trihalides, to give the corresponding 16alpha-methyl-14beta,16beta-ethano 17-ketone. Similar rearrangements are described for epimeric 14,17-bridged estradiol analogues, leading to 16beta-methyl-14alpha,16alpha-ethano 17-ketones. By contrast, acid-mediated reactions of 3-methoxy-14,17alpha-ethenoestra-1,3,5(10)-trien-17beta-ol 11 display reagent dependence, leading to products of competing 16(17-->17(1))abeo-and 15(14-->17(2))abeo-rearrangements. Conversion of certain rearrangement products into 14,16-ethano analogues of estradiol and 19-nortestosterone are described, and X-ray crystallographic structure determinations are reported for three ring-D-bridged compounds, and a novel spiro compound arising from rearrangement of the 14alpha, 17alpha-etheno 17beta-alcohol 11.