Synthesis, crystal and molecular structure of a 1,11-etheno-steroid: 3-methoxy-1,11-ethenoestra-1,3,5(10),9(11)-tetraen-17-one

Abstract

Methods of construction of a two carbon bridge between C(1) and C(11) of the steroid skeleton have been studied. Treatment of 17,17-ethylenedioxy-11α-ethynyl-3-methoxyestra-1,3,5(10)-trien-11β-ol (2) with toluene-p-sulphonic acid in benzene gave a mixture of 3-methoxy-1′ξ-methyl-1,11ξ-methanoestra-1,3,5(10),6,8,-pentaen-17-one (7) and the title compound (8). The latter was also obtained in poor yield from 17,17-ethylenedioxy-3-methoxy-11α-(2-oxoethyl)estra-1,3,5(10)-trien-11β-ol (4) in hydrogen fluoride and in better yield (76%) from treatment of (2) with tris(triphenylsilyl) vanadate. Crystals of (8) are orthorhombic, space group P2₁2₁2₁, a= 7.867(5), b= 30.036(20), c= 6.838(5)Å, Z= 4. The structure was solved by direct methods and refined by full-matrix least-squares calculations to R 0.044 over 1 283 statistically significant reflections from diffractometer measurements. The modified steroid skeleton is very flat, the maximum deviation of any ring atom from the naphthalene plane being 0.635 Å. Ring B approximates to a C(7)α-envelope form, ring C adopts a half-chair conformation, and ring D has a C(14)α-envelope form.