The crystal and molecular structure of 3β-acetoxy-7α,11α,-dibromolanostane-8α,9α-epoxide

Abstract

The structure of 3β-acetoxy-7α,11α-dibromolanostane-8α,9α-epoxide, the dibromo-derivative of an intermediate in an attempted removal of the 14α-methyl group of 3β-acetoxylanost-8-ene, has been determined by X-ray analysis. Crystals of the derivative, C₃₂H₅₂O₃Br₂, are orthorhombic, a= 26·03₅, b= 9·89₅, c= 12·26₈Å, Z= 4, space group P2₁2₁2₁. The intensities of 2236 reflexions were measured using Cu-K_α radiation. The two bromine positions were determined by Patterson methods and all carbon and oxygen atoms were located on three successive three-dimensional electron-density distributions. Positional and isotropic temperature parameters were refined by four cycles of least-squares; a further six cycles of anisotropic least-squares completed the refinement, giving a final R value of 13·3%. The absolute configuration was determined by the anomalous dispersion method.

The derivative has ring A in the normal chair form and ring D in a half-chair conformation. The epoxide bridge prevents rings B and C from adopting the chair form. The bond lengths and valency angles are normal, and the intermolecular separations correspond to Van der Waals interactions.