3-[2-(3-Phenyl-2-oxo-1,2-dihydroquinoxalin-1-yl)ethyl]-1,3-oxazolidin-2-one

The dihydroquinoxaline ring system of the title molecule, 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 molecular conformation is enforced by C—H⋯O hydrogen bonds. In the crystal, molecules are linked by weak C—H⋯O hydrogen bonds, forming a three-dimensional network.


El Ammari Comment
Among the various classes of nitrogen containing heterocyclic compounds, quinoxaline derivatives display a broad spectrum of biological activities (Seitz et al., 2002;Monge et al., 1993;Kim et al., 2004). Quinoxalines play an important role as a basic skeleton for the design of a number of antibiotics such as echinomycin, actinomycin and leromycin. It has been reported that these compounds inhibit the growth of gram-positive bacteria and are also active against various transplantable tumors (Bailly et al., 1999). As a continuation of our research work devoted to the development of substituted dihydroquinoxalin-1-yl derivatives (Caleb et al., 2009) we report in this paper the synthesis and the crystal structure of the title compound.
The two fused six-membered rings (N1/N2/C1-C8) building the molecule of the title compound are approximately planar, the largest deviation from the mean plane being -0.055 (2) Å at C6 (Fig. 1). However, the plane through the two fused rings is slightly folded around the C1-C6 direction as indicated by the dihedral angle between them of 4.75 (8)°.
The fused-ring system is linked to the phenyl ring (C10-C15) and to make a dihedral angle of 30.77 (9)°. The oxazolidin cycle (O2/N3/C18/C19/C20) is connected to the fused rings through the C16-C17 chain and build with them a dihedral angle of 68.42 (10)°. The molecular conformation is tabilized by intramolecular C-H···O hydrogen bonds (Table 1).

Experimental
In a 100 ml flask 3-phenyl-quinoxalin-2-one (1.25 mmol, 0.28 g) was reacted with dichloroethylamine hydrochloride (2.66 mmol, 0.50 g) in 40 ml of DMF in presence of K 2 CO 3 (4 mmol, 0.52 g) and tetra-n-butylammonium bromide (0.01 mmol, 0.0032 g). The mixture was brought to reflux in a sand bath with magnetic stirring. The reaction progress was monitored by thin layer chromatography. After evaporation of the solvent under reduced pressure, the residue obtained was chromatographed on silica column (hexane/ethyl acetate 4:6 v/v). Recrystallization occurred in the same eluent.

Refinement
H atoms were located in a difference map and treated as riding with C-H = 0.93-0.97 Å, and with U iso (H) = 1.2 U eq (C).
In the absence of significant anomalous scattering, the absolute configuration could not be reliably determined and thus 2216 Friedel pairs were merged and any references to the Flack parameter were removed.

Figure 1
The molecular structure of the title compound with displacement ellipsoids drawn at the 50% probability level. H atoms are represented as small circles or arbitrary radius.  Partial crystal packing of the title compound showing the hydrogen-bonding network (dashed lines). where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.21 e Å −3 Δρ min = −0.23 e Å −3 Special details Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. Refinement. Refinement of F 2 against all reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on all data will be even larger.