1,7-Dimethyl-penta-cyclo-[5.4.0.0.0.0]undecane-8,11-dione.

The structure of the title compound, C(13)H(14)O(2), a penta-cyclo-undecane cage derivative, exhibits unusual Csp(3)-Csp(3) single-bond lengths ranging from 1.505†(3) to 1.607†(2)†à and strained bond angles as small as 88.7†(1)° and as large as 121.0†(2)°. In this meso compound, an inter-nal non-crystallographic mirror plane exists, bis-ecting the mol-ecule. In the crystal, weak C-H⋯O hydrogen bonds link the mol-ecules into an infinite spiral about a twofold screw axis along the [100] direction.