3-[2-(3-Phenyl-2-oxo-1,2-di-hydro-quin-oxalin-1-yl)eth-yl]-1,3-oxazolidin-2-one.

The di-hydro-quinoxaline ring system of the title mol-ecule, C19H17N3O3, is approximately planar [maximum deviation = 0.050 (2) Å], the dihedral angle between the planes through the two fused rings being 4.75 (8)°. The mean plane through the fused-ring system forms a dihedral angle of 30.72 (5)° with the attached phenyl ring. The mol-ecular conformation is enforced by C-H⋯O hydrogen bonds. In the crystal, mol-ecules are linked by weak C-H⋯O hydrogen bonds, forming a three-dimensional network.

1-Phenyl-3H-2,3-benzodiazepin-4(5H)-one.

The seven-membered ring in the title compound, C(15)H(12)N(2)O, adopts a boat-shaped conformation (with the methyl-ene C atom as the prow and the double-bond C=N pair of atoms as the stern). In the crystal, adjacent mol-ecules are linked by an N-H⋯O hydrogen bond to generate helical chains running along the a axis of the ortho-rhom-bic unit cell.

3-{2-[(3-Phenyl-quinoxalin-2-yl)-oxy]ethyl}-1,3-oxazolidin-2-one.

The asymmetric unit of the title compound, C(19)H(17)N(3)O(3), consists of two independent mol-ecules that are disposed about a pseudo-centre of inversion. The plane of the phenyl substituent is twisted by 38.1 (1)° [43.6 (1)° in the second mol-ecule] out of the plane of the quinoxaline ring system. The five-membered ring of the substituent at the 2-position adopts an envelope conformation; the 5-CH(2) atom representing the flap lies out of the plane defined by the other four atoms [deviation 0.264 (7) Šin the first mol-ecule and 0.291 (6) Šin the second]. The dihedral angle between the five-membered ring and the 4-phenyl ring is 84.9 (1)° while that between the five-membered ring and the 5-phenyl ring is 65.6 (1)°.