6,7-Dichloro-3-(2,4-dichlorobenzyl)quinoxalin-2(1H)-one

In the title compound, C15H8Cl4N2O, the quinoxaline ring system is almost planar, with a dihedral angle between the benzene and pyrazine rings of 3.1 (2)°. The 2,4-dichlorophenyl ring is approximately perpendicular to the pyrazine ring, with a dihedral angle of 86.47 (13)° between them. The crystal packing features intermolecular N—H⋯O hydrogen bonds and π–π stacking interactions, with centroid–centroid distances in the range 3.699 (3)–4.054 (3) Å.

In the title compound, C 15 H 8 Cl 4 N 2 O, the quinoxaline ring system is almost planar, with a dihedral angle between the benzene and pyrazine rings of 3.1 (2) . The 2,4-dichlorophenyl ring is approximately perpendicular to the pyrazine ring, with a dihedral angle of 86.47 (13) between them. The crystal packing features intermolecular N-HÁ Á ÁO hydrogen bonds andstacking interactions, with centroid-centroid distances in the range 3.699 (3)-4.054 (3) Å .   Table 1 Hydrogen-bond geometry (Å , ).
In the molecular structure ( Fig. 1), the quinoxaline ring system is nearly planar with a dihedral angle between the phenyl and pyrazine rings of 3.12(0.22) ° and rms deviations of 0.0135 Å and 0.0210 Å, respectively. The largest deviations from the planes of the two rings are 0.020 (3) Å for C3 and 0.031 (3) Å for C1. The 2,4-dichlorophenyl and pyrazine rings are approximately orthogonal with a dihedral angle of 86.47 (13) ° between them.

Experimental
In a 10 ml Emrys reaction vial, 4-(2,4-dichlorobenzylidene)-2-phenyloxazol -5(4H)-one (0.32 g, 1 mmol), 4,5-dichlorobenzene-1,2-diamine (0.18 g, 1 mmol), TFA (0.23 g, 2 mmol) and ethylene glycol (1.5 ml) were mixed and then capped (The automatic mode stirring helped the mixing and uniform heating of the reactants). The mixture was heated for 16 min at 393 K under microwave irradiation. Upon completion, monitored by TLC, the reaction mixture was cooled to room temperature. The solid product was poured into water and neutralized with 10% NaOH, and then collected by filtration, subsequently washed with ethanol and ethylether in sequence to give a pure yellow solid. A single-crystal suitable for Xray diffraction was obtained from the evaporation of a solution of the title compound in ethanol.

Refinement
All H atoms were placed in calculated positions, with N-H = 0.86 Å, and C-H=0.93 Å or 0.97 Å and included in the final cycles of refinement using a riding model, with Uĩso~(H) = 1.2U~eq~(parent atom).

Figure 1
The structure of (I), showing 30% probability displacement ellipsoids and the atom-numbering scheme.  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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq