(25R)-16β-Acetoxy-3β-bromo-23′,26-epoxy-23′,25-dimethyl-5α-cholest-23,23′-en-6-one dichloromethane monosolvate

The crystal structure of the title compound, C31H45BrO5·CH2Cl2, prepared in six steps from diosgenin, confirmed that the configurations of the stereogenic centers, positions 20S and 25R, remain unchanged during the reaction. The six-membered A, B and C rings have chair conformations. The five-membered ring D has an envelope conformation (with the methyl-substituted C atom fused to ring C as the flap) and the six-membered dihydropyran ring E adopts a twist-boat conformation. In the crystal, molecules are linked via C—H⋯O and C—H⋯Cl hydrogen bonds, the latter involving the dichloromethane solvent molecule, forming a three-dimensional supramolecular network.

The crystal structure of the title compound, C 31 H 45 BrO 5 Á-CH 2 Cl 2 , prepared in six steps from diosgenin, confirmed that the configurations of the stereogenic centers, positions 20S and 25R, remain unchanged during the reaction. The sixmembered A, B and C rings have chair conformations. The five-membered ring D has an envelope conformation (with the methyl-substituted C atom fused to ring C as the flap) and the six-membered dihydropyran ring E adopts a twist-boat conformation. In the crystal, molecules are linked via C-HÁ Á ÁO and C-HÁ Á ÁCl hydrogen bonds, the latter involving the dichloromethane solvent molecule, forming a threedimensional supramolecular network.
In the crystal, molecules are linked by C-H···O and C-H···Cl hydrogen bonds (Table 1), the latter involve the dichloromethane solvent molecule, forming a three-dimensional supramolecular architecture.
The solvent was evaporated under vacuum and the organic phase extracted with CH 2 Cl 2 -water, neutralized with NaHCO 3 and dried over Na 2 SO 4 to give a 0.160 g (61% yield) as white crystals which were purified by chromatography using a Spectroscipic data for the title compound are given in the archived CIF.

Refinement
All H atoms were placed in calculated positions and treated as riding atoms: C-H = 0.98, 0.97 and 0.96 Å for CH, CH 2 and CH 3 H atoms, respectively, with U iso (H) = k × Ueq(C), where k = 1.5 for CH 3 H atoms and = 1.2 for other H atoms.

Computing details
Data collection: COLLECT (Nonius, 1999); cell refinement: SCALEPACK (Otwinowski & Minor, 1997); data reduction: DENZO and SCALEPACK (Otwinowski & Minor, 1997); program(s) used to solve structure: SHELXS97 (Sheldrick 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: PLATON (Spek, 2009); software used to prepare material for publication: WinGX (Farrugia, 2012   where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.75 e Å −3 Δρ min = −0.68 e Å −3 Extinction correction: SHELXL97 (Sheldrick, 2008), Fc * =kFc[1+0.001xFc 2 λ 3 /sin(2θ)] -1/4 Extinction coefficient: 0.0038 (10) Absolute structure: Flack (1983) Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'s involving l.s. planes. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > 2σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq