Redetermined structure, inter­molecular inter­actions and absolute configuration of royleanone

The structure of the title diterpenoid, C(20)H(28)O(3), {systematic name: (4bS,8aS)-3-hy­droxy-2-isopropyl-4b,8,8-trimethyl-4b,5,6,7,8,8a,9,10-octa­hydro­phenanthrene-1,4-dione} is confirmed [Eugster et al. (1993 ▶). Private communication (refcode HACGUN). CCDC, Union Road, Cambridge] and its packing is now described. Its absolute structure was established by refinement against data collected with Cu radiation: the two stereogenic centres both have S configurations. One cyclo­hexane ring adopts a chair conformation whereas the other cyclo­hexane ring is in a half-chair conformation and the benzoquinone ring is slightly twisted. An intra­molecular O—H⋯O hydrogen bond generates an S(5) ring motif. In the crystal, mol­ecules are linked into chains along [010] by O—H⋯O hydrogen bonds and weak C—H⋯O inter­actions. The packing also features C⋯O [3.131 (3) Å] short contacts.