1,4-Bis(3-chloropyrazin-2-yloxy)benzene

In the title compound, C14H8Cl2N4O2, the pyrazine rings are orthogonal to the benzene ring, making dihedral angles of 88.42 (8) and 89.22 (8)°. The Cl atoms attached to the pyrazine rings deviate by −0.0597 (5) and 0.0009 (5) Å from the ring plane. The crystal structure features C—H⋯N hydrogen bonds.


Comment
The pyrazine ring is a useful structural unit in medicinal chemistry and has found broad applications in drug development and can be used as antiproliferative agent (Dubinina et al., 2006), potent CXCR3 antagonist (Du et al., 2009), CB1 antagonist (Ellsworth et al., 2007 and c-Src inhibitor (Mukaiyama et al., 2007). In view of different applications of this class of compounds, we have undertaken the single-crystal structure determination of the title compound.
The bond distances and angles in the title compound ( Fig. 1) agree very well with the corresponding bond distances and angles reported in a closely related compound (Nasir et al., 2010). In the titled compound, the pyrazine ring (N1/N2/C1-C4) makes a dihedral angle of 88.42 (8)° with the benzene ring (C5-C10), which shows that these are orthogonal to each other. The other pyrazine ring (N3/N4/C11-C14) makes a dihedral angle of 89.22 (8)° with the bezene ring, which also shows that these are also orthogonal to each other. The dihedral angle between the two pyrazine rings is 3.18 (7)°. The chlorine atoms Cl1 and Cl2 attached with the pyrazine rings deviate by -0.0597 (5) and 0.0009 (5)Å. The crystal packing is stabilised by intermolecular C-H···N hydrogen bonds (Tab. 1 & Fig. 2).

Experimental
To a stirred solution of Cs 2 CO 3 /K 2 CO 3 (22 mmol) in CH 3 CN (50 mL), dihydroxybenzenes (10 mmol) was added and stirred for 5 min. 2,3-Dichloropyrazine (20 mmol) in CH 3 CN (100 mL) was added dropwise to the above reaction mixture and stirring was allowed at refluxing condition for 12 h. After the reaction was complete, the reaction mixture was allowed to attain room temperature and then evaporated to dryness. The residue obtained was extracted with CH 2 Cl 2 (3 x 100 mL), washed with water (3 x 100 mL), brine and then dried over Na 2 SO 4 . Evaporation of the organic layer gave a residue, which on purification using column chromatography with hexane/CHCl 3 (1:1) as an eluent gave the corresponding compound. Single crystals suitable for X-ray diffraction were obtained by slow evaporation of a solution of the title compound in hexane at room temperature.

Refinement
The hydrogen atoms were placed in calculated positions with C-H = 0.93 Å, refined in the riding model with fixed isotropic displacement parameters: U iso (H) = 1.2U eq (C).  The molecular structure of the title compound, showing displacement ellipsoids drawn at the 30% probability level. H atoms are presented as small spheres of arbitrary radius.

Figure 2
The crystal packing of the title compound viewed down c axis. H-atoms not involved in H-bonds have been excluded for clarity. Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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 > 2sigma(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.