1-{3-[(4-Oxopiperidin-1-yl)carbon­yl]benzoyl}piperidin-4-one

Two independent mol­ecules comprise the asymmetric unit in the title compound, C(18)H(20)N(2)O(4). One of the mol­ecules exhibits disorder in one of its 4-piperidone rings, which is disposed over two orientations [site occupancy of the major component = 0.651 (5)]. The first independent mol­ecule and the minor component of the second disordered mol­ecule are virtually superimposable. The central four C atoms in the major component of the disordered mol­ecule have an opposite orientation. All the 4-piperidone rings have a chair conformation. The carbonyl groups in each mol­ecule have approximate anti conformations [O=C⋯C=O = 146.2 (2) and −159.9 (2)°]. The 4-piperidone rings lie to opposite sides of the central benzene ring in both mol­ecules. In the crystal, mol­ecules are linked by C—H⋯O inter­actions. The crystal studied was found to be a non-merohedral twin (twin law −1 0 0, 0 1 0, 0 − 1/2 − 1), the fractional contribution of the minor component being approximately 11%.