(±)-(4bS,8aR,10aS)-10a-Ethynyl-4b,8,8-trimethyl-3,7-dioxo-3,4b,7,8,8a,9,10,10a-octa­hydro­phenanthrene-2,6-dicarbonitrile

The anti-inflammatory and cytoprotective tricyclic title compound, C₂₁H₁₈N₂O₂, also known as TBE-31, crystallizes with two nearly superimposable mol­ecules in the asymmetric unit. In both mol­ecules, the three ring systems conform to an envelope–chair–planar arrangement. The central ring, in a cyclohexane chair conformation, contains an axial ethynyl group that bends slightly off from a nearby axial methyl group because of the 1,3-diaxial repulsion between the two groups. In the crystal, weak C—H...N and C—H...O inter­actions form chains along [001].