Pyrazino[2,3-b]indolizine-10-carbonitrile

In the crystal structure of the title compound, C11H6N4, neighbouring molecules are linked into inversion dimers through pairs of weak C—H⋯N hydrogen bonds, forming an R 2 2(10) ring motif. The dimers forming this motif are further linked by π–π interactions. With respective average deviations from planarity of 0.004 (2) and 0.004 (1) Å, the pyrazino[2,3-β]indolizine and cyano fragment are oriented at 0.8 (1)° to each other. The mean planes of the pyrazino[2,3-b]indolizine skeleton either lie parallel or are inclined at an angle of 28.7 (2)° in the crystal.

In the crystal structure of the title compound, C 11 H 6 N 4 , neighbouring molecules are linked into inversion dimers through pairs of weak C-HÁ Á ÁN hydrogen bonds, forming an R 2 2 (10) ring motif. The dimers forming this motif are further linked byinteractions. With respective average deviations from planarity of 0.004 (2) and 0.004 (1) Å , the pyrazino[2,3-]indolizine and cyano fragment are oriented at 0.8 (1) to each other. The mean planes of the pyrazino[2,3-b]indolizine skeleton either lie parallel or are inclined at an angle of 28.7 (2) in the crystal.
Symmetry code: (i) Àx þ 1; Ày; Àz.  (1) Symmetry codes: (ii) À1 þ x; y; z. Notes: CgA and CgB are the centroids of the N1/C6-C8/C13 and N1/C2-C6 rings, respectively. The dihedral angle is that between the planes of the rings CgI and CgJ. The interplanar distance is the perpendicular distance of CgI from ring J. The offset is the perpendicular distance of ring I from ring J.

Comment
Pyrazines play an important role as building block of many pharmaceutical products. They occur in many compounds with pharmaceutical and flavoring applications. Many of them have been found in nature. Pyrazines are responsible for flavour in foodstuffs, e.g. cheese, tea, coffee or cooked meat. (Akiyama et al., 1978;Mussinan et al., 1973). Biological activities of pyrazine derivatives are widely discussed in plentiful scientific publications: antibacterial (Foks et al., 2005), anti-inflammatory (Petrusewicz et al., 1995), chemotherapeutic agent (Kushner et al., 1952), antimycobacterial (Seitz et al., 2002) and antithrombotic (Petrusewicz et al., 1993). Such pharmacological activities in group of pyrazine are possibly the result of their structures. It is known that the pyrazine-acetonitrile shows antiplatelet and analgestic activity (Kaliszan et al., 1985). X-Ray structure of pyrazino[2,3-β]indolizine-10-carbonitrile is subject of the present paper.
In the crystal structure, neighbouring molecules are linked through weak C-H···N hydrogen bond forming R 2 2 (10) ring motif (Table 1 and Fig. 2). Molecules which forming this motif are linked by π-π interactions between the central ring A and the lateral rings B (Table 2 and Fig. 2). All the interactions demonstrated were found by PLATON (Spek, 2009).

Experimental
Pyrazino[2,3-β]indolizine-10-carbonitrile was obtained by mixing 2,3-dichloropyrazine, 2-pyridylacetonitrile and potassium carbonate in DMSO. The mixture was stirred for 5 h at 333 K. After cooling the reaction mixture to room temperature, water was added. Then mixture was acidified with hydrochloric acid Foks, 1981 and1982). The orange-green precipitate was obtained. Single crystals suitable for X-ray analysis were grown in methanol solution (m. p. = 486 K).

Refinement
All H atoms were positioned geometrically and refined using a riding model, with C-H = 0.93Å and U iso (H) = 1.2U eq (C).
supplementary materials sup-2 Figures   Fig. 1. The molecular structure of the title compound showing the atom-labeling scheme. Displacement ellipsoids are drawn at the 25% probability level and H atoms are shown as small spheres of arbitrary radius. CgA and CgB denote the ring centroids.

Special details
Experimental. Empirical absorption correction using spherical harmonics, implemented in SCALE3 ABSPACK scaling algorithm.
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 > σ(F 2 ) is used only for calculating Rfactors(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.   (1) Symmetry codes: (ii) -1 + x, y, z. Notes: CgA and CgB are the centroids of the N1/C6-C8/C13 and N1/C2-C6 rings, respectively. The dihedral angle is that between the planes of the rings CgI and CgJ. The interplanar distance is the perpendicular distance of CgI from ring J. The offset is the perpendicular distance of ring I from ring J.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
supplementary materials sup-6