Lup-20(29)-en-28-ol-3-one (betulone).

The asymmetric unit of the title compound, C30H48O2, contains two independent mol-ecules, the main difference between them being that the isopropenyl group is rotated by approximately 180°. In each mol-ecule, the fused six-membered rings have chair-chair-chair-chair conformations and the cyclo-pentane ring adopts an envelope conformation with the C atom bearing the hy-droxy-methyl group as the flap. All ring junctions are trans-fused. With the exception of one of the methyl groups adjacent to the C=O group, all the methyl groups are in axial positions. The isopropenyl group is equatorial and the hy-droxy-methyl group is in an axial orientation. In the crystal, weak C-H⋯O inter-actions link the mol-ecules into chains along [010]. Weak intra-molecular C-H⋯O hydrogen bonds are also observed but the hy-droxy groups are not involved in hydrogen bonds.