(22E,24R)-5α-Ergosta-2,22-dien-6-one

In the title molecule, C28H44O, two six-membered rings have regular chair conformations, while the six-membered ring containing the C=C double bond exhibits a distorted chair conformation. The five-membered ring adopts an envelope conformation. In the crystal, weak intermolecular C—H⋯O interactions link molecules into chains along the b axis. The absolute configuration was assigned to correspond with that of the known chiral centres in a precursor molecule.

In the title molecule, C 28 H 44 O, two six-membered rings have regular chair conformations, while the six-membered ring containing the C C double bond exhibits a distorted chair conformation. The five-membered ring adopts an envelope conformation. In the crystal, weak intermolecular C-HÁ Á ÁO interactions link molecules into chains along the b axis. The absolute configuration was assigned to correspond with that of the known chiral centres in a precursor molecule.

Comment
In continuation of our structural study of brassinolide analogs (Sheng et al., 2011), we present here the crystal structure of the title compound, (I). In (I) (Fig. 1), ring A shows a distorted chair confirmation, and atoms C1, C2, C3 and C4 are coplanar with the r.m.s. deviation of 0.007 (1) Å for the C=C bond; atoms C5 and C10 deviate at 0.329 (4) Å and -0.423 (4) Å from this mean plane, respectively. Rings B and C have regular chair conformation each; while ring D has an envelope conformation.
Weak intermolecular C-H···O interactions (Table 1) link the molecules related by translation along the axis b into chains.

Refinement
C-bound H atoms were placed at calculated positions (C-H 0.95-1.00 Å) and constrained to ride on their parent atoms, withU iso (H) = 1.2-1.5 U eq (C). Because of negligible anomalous scattering effects, 2305 Friedel pairs were averaged in the refinement. The absolute configuration was assigned to correspond with that of the known chiral centres in a precursor molecule, which remained unchanged during the synthesis of the title compound. Fig. 1. The molecular structure of (I) shown with 30% probability displacement ellipsoids.

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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 > 2sigma(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.  0.0236 (9) 0.0301 (11) 0.0194 (9) 0.0024 (9) 0.0020 (7) 0.0016 (8)