Ketazolam.

The title compound, 11-chloro-8,12b-dihydro-2,8-dimethyl-12b-phenyl-4H-[1,3]oxazino[3,2-d][1,4]benzodiazepine-4,7(6H)-dione, C20H17ClN2O3, is a benzodiazepine with an additional d-face-fused heterocyclic ring. In the molecule, a dihedral angle of 86.2 (1) degrees is formed by the planes of the phenyl and benzo rings and the former is axially oriented from the core, i.e. the fused 6,7,6-tricyclic system. Both heterocycles in the core suffer significant deviations from planarity. The central diazepine ring is a twist-boat and the oxazine ring exhibits a conformation intermediate between half-chair and sofa.