12α-Hydroxy-3,27-dioxooleanano-28,13-lactone

There are two independent molecules in the asymmetric unit of the title compound, C30H44O5. They comprise a triterpenoid skeleton of five six-membered rings and a five-membered lactone ring. The five six-membered rings are all trans-fused. In both independent molecules the D rings adopt a slightly distorted half-chair conformation due the presence of the lactone ring while the other four six-membered rings all adopt chair conformations. The characteristic carbon–carbon double bond of the oleanoic skeleton is absent. Intermolecular O—H⋯O hydrogen bonds between the hydroxy and carbonyl groups occur in the crystal structure.

There are two independent molecules in the asymmetric unit of the title compound, C 30 H 44 O 5 . They comprise a triterpenoid skeleton of five six-membered rings and a five-membered lactone ring. The five six-membered rings are all trans-fused. In both independent molecules the D rings adopt a slightly distorted half-chair conformation due the presence of the lactone ring while the other four six-membered rings all adopt chair conformations. The characteristic carbon-carbon double bond of the oleanoic skeleton is absent. Intermolecular O-HÁ Á ÁO hydrogen bonds between the hydroxy and carbonyl groups occur in the crystal structure. H atoms treated by a mixture of independent and constrained refinement Á max = 0.18 e Å À3 Á min = À0.23 e Å À3 Table 1 Hydrogen-bond geometry (Å , ).  (2) 172 (2) Symmetry codes: (i) x À 1 2 ; Ày þ 1 2 ; Àz; (ii) Àx þ 2; y À 1 2 ; Àz þ 1 2 .
To a solution of oxime in dioxane and AcOH, aqueous TiCl 3 was added under ice, keeping temperature of 299 K by cooling, for 4 h to give imine. To imine in dioxane and AcOH, an aqueous solution of NaNO 2 was added for 1 h to obtain the title compound. Crystals suitable for X-ray structure analysis were obtained by slow evaporation of a solution in methanol at room temperature.

Refinement
H atoms of the hydroxy group were located in a difference density map and refined freely. Other H atoms were positioned geometrically and refined as riding (C-H = 0.95-1.00 Å) and allowed to ride on their parent atoms, with U iso (H) = 1.2U eq or 1.5U eq (parent). The absolute configuration could not be established because of the absence of significant anomalous effects. Friedel pairs were merged for the final cycles of refinement.

Figure 1
The two molecules of an asymmetric unit of (I) with the atom-labelling scheme. Displacement ellipsoids are drawn at the 60% probability level and H atoms have been omitted for clarity.

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'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 > σ(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.