3-Oxo-18α-olean-28,13ß-olide.

The title terpene, C(30)H(46)O(3), is a 28,13ß-lactone of oleanolic acid prepared with bis-muth trifluoro-methane-sulfonate (OTf), Bi(OTf)(3)·xH(2)O. All rings are trans-fused. The X-ray study shows the inversion of the orientation of 18-H in the lactonization reaction. A quantum chemical ab-initio Roothaan Hartree-Fock calculation of the equilibrium geometry of the isolated mol-ecule gives values for bond lengths and valency angles in close agreement with experimental values. The calculation also reproduces the observed mol-ecular conformation, with puckering parameters that agree well with those determined from the crystallographic study.