Conformational study of a photochemical cyclopentenone rearrangement. Molecular mechanics calculations and X-ray structure of 14β-hydroxy-5-methoxy-de-A-oestra-5,7,9,16-tetraen-15-one

Abstract

Molecular mechanics calculations show two minimum energy conformers for the title ketol (1), both having a ring c-sofa conformation. X-Ray crystal structure analysis shows that of these the 12β-sofa conformation is adopted in the ketol [ΔC_s(8)= 1.7°] and ring D assumes a flattened C(14)-envelope conformation with C(14) displaced 0.315 Å below the plane of C(13), C(17), C(16), and C(15). Crystallographic data are a= 8.591(7), b= 7.969(5), c= 10.089(7)Å, Z= 2, space group P₂₁. In the preferred conformer there is significant orbital overlap between the two isolated chromophores.