3β-Hydroxy-28-norolea-12,17-dien-11-one

The title compound, C₂₉H₄₄O₂, was formed by treatment of 11-oxooleanolic acid under strong alkaline conditions. The absolute structure of the chiral mol­ecules could not be determined reliably from the diffraction data, but is known from other triterpenes. The asymmetric unit consists of two mol­ecules, 1 and 2. In both mol­ecules, rings A and B show chair conformations. The other rings show mixed forms between envelope and half-chair conformations with atoms in positions 8, 15 and 21 forming the flaps in rings C, D and E, respectively. Rings D and E of mol­ecule 2 are disordered over two orientations, with occupancies of 0.557 (4) and 0.443 (4), which differ in the direction of the flap in ring E. In the crystal, mol­ecules 1, as well as the mol­ecules 2, are linked by O—H...O hydrogen bonds, forming chains parallel to the b axis.