19β,28-Epoxy-18α-olean-3β-ol

The title triterpene, C30H50O2, is an 18α-oleanane derivative prepared by the Wagner–Meerwein rearrangement of betulin with Bi(OTf)3.xH2O (OTF is trifluoromethanesulfonate). There are two symmetry-independent molecules in the asymmetric unit that show no significant differences concerning bond lengths and angles. The conformation of the six-membered rings is close to a chair form, while the five-membered epoxide rings adopt envelope conformations. All rings are trans-fused. In the crystal, molecules are held together by O—H...O hydrogen bonds. A quantum-mechanical ab initio Roothan Hartree–Fock calculation on the isolated molecule gives values for bond lengths and valency angles close to the experimental values. The calculations also reproduce well the molecular conformation with calculated puckering parameters that match well the observed values.