9-Phenyl-3,4,4a,9a-tetrahydrotri­ptycene and 9-phenyl-1,2,3,4,4a,9a-hexa­hydro­triptycene

The structure of 9-phenyl-3,4,4a,9a-tetra­hydro­triptycene, C₂₆H₂₂, (I), exhibits regiochemistry consistent with a stepwise mechanism for its formation from photo­cyclo­addition of 1,3-cyclo­hexa­diene and 9-phenyl­anthracene. Bond distances involving the bridgehead C atoms are similar in (I) and the hydrogenated derivative, 9-phenyl-1,2,3,4,4a,9a-hexa­hydro­triptycene, C₂₆H₂₄, (II), with bonds to the quaternary-C atoms exhibiting significant elongation [1.581 (2) Å in (I) and 1.585 (2) Å in (II)]. The molecular geometry precludes significant σ–π overlap between the phenyl groups and the interannular bonds in both compounds, indicating that the origin of the bond lengthening is steric in nature.