Synthesis, crystal structure and Hirshfeld surface analysis of 1-[3-(2-oxo-3-phenyl-1,2-dihydroquinoxalin-1-yl)propyl]-3-phenyl-1,2-dihydroquinoxalin-2-one

In the title compound, the dihydroquinoxaline units are both essentially planar and the dihedral angle between their mean planes is 64.82 (2)°. In the crystal, C—H⋯O hydrogen bonds form chains along the b-axis direction which are joined by π-stacking and C—H⋯π(ring) interactions into the full three-dimensional network structure.


Chemical context
The family of nitrogenous drugs, notably those containing the quinoxaline moiety, is important in medicinal chemistry because of the wide range of pharmacological activities exhibited, including antibacterial, antituberculosis, antiinflammatory, antifungal anti-glycation, anti-analgesic and anticancer properties.In particular, quinoxalin-2-one derivatives are a class of heterocyclic compounds with different applications in various fields (Ramli et al., 2014).They have been studied intensively as an important heterocyclic system for the synthesis of biologically active compounds ranging from herbicides and fungicides to therapeutically usable drugs (Ramli & Essassi, 2015).These chemicals are active antitumor agents with tyrosine kinase receptor inhibition properties (Galal et al., 2014).They can also selectively antagonize the glycoprotein in cancer cells (Sun et al., 2009).Quinoxalin-2-one derivatives are also potential antagonist ligands for imaging the A2A adenosine receptor by positron emission tomography (PET) (Holschbach et al., 2005).Given the wide range of therapeutic applications for such compounds, we have previously reported a route for the preparation of quinoxalin-2-one derivatives using N-alkylation reactions carried out with di-halogenated carbon chains (Missioui et al. 2022;Abad et al., 2024).A similar approach yielded the title compound, C 31 H 24 N 4 O 2 (Fig. 1).In addition to the synthesis, we also report the molecular and crystal structure along with a Hirshfeld surface analysis.

Structural commentary
The title compound crystallizes in the triclinic space group P1 with one molecule in the asymmetric unit (Fig. 2).The dihydroquinoxaline unit containing N1 is planar to within 0.038 (1) A ˚(r.m.s.deviation of fitted atoms = 0.0209 A ˚) while that containing N3 is planar to within 0.021 (1) A ˚(r.m.s.deviation = 0.0124 A ˚).The dihedral angle between their mean planes is 64.82 (4) � .The C9-C14 benzene ring is inclined to the plane of the dihydroquinoxaline unit containing N1 by 7.35 (5) � , which is due in part to an intramolecular C10-H10� � �O1 hydrogen bond (Table 1).The corresponding angle on the other half of the molecule is 37.63 (5) � .The greater out-of-plane orientation of the latter phenyl ring may be the result of its participation in C-H� � ��(ring) interactions (Table 1 and Fig. 3).There are close contacts of H29A with O1 (2.31A ˚) and H31B with O2 (2.32 A ˚), which might be considered additional hydrogen-bond interactions although the C-H� � �O angles are only 102 � .The central C-C-C unit extends out from N3 in an all-trans conformation with a C29-C30-C31-N3 torsion angle of À 175.74 (9) � but this does not continue to the second quinoxaline unit as the N1-C29-C30-C31 torsion angle is À 69.98 (13) � .

Figure 2
The title molecule with labeling scheme and 50% probability ellipsoids.
Cg6 is the centroid of the C23-C28 benzene ring.

Figure 3
Perspective view of the chains formed by C-H� � �O hydrogen bonds (dashed lines).

Figure 1
Synthesis of the title compound.

Hirshfeld surface analysis
To quantify the intermolecular interactions, the Hirshfeld surface was calculated with CrystalExplorer 21.5 (Spackman et al., 2021).Descriptions of the plots generated and their interpretation have been published previously (Tan et al., 2019).Fig. 6 shows the d norm surface plotted over the range   À 0.1072 to 1.3548 a.u.together with two neighboring molecules and the connecting C-H� � �O hydrogen bonds.The red spots on the surface clearly indicate the sites of these interactions.Fig. 7 shows the surface plotted over the shape-index with three neighboring molecules included.The pattern of blue and orange triangles marking a site of �-stacking interactions is clearly visible in the upper right of the surface with the interaction denoted by two lines.On the lower left, the C-H� � ��(ring) interaction is shown by a third line.The 2-D fingerprint plots (Fig. 8) show that the greatest contribution to the total intermolecular interactions is from H� � �H contacts at 49.6% (Fig. 8a), which is expected due to the significant hydrogen content and the fact that most of the hydrogen atoms are attached to aromatic rings.The other large contribution is from C� � �H/H� � �C contacts (23.0%,Fig. 8b), which come primarily from the C-H� � ��(ring) interactions.In addition, there are O� � �H/H� � �O contacts (7.4%, Fig. 8c), C� � �C contacts (5.8%, Fig. 8d) and N� � �H/H� � �N contacts (5.2%, Fig. 8e).The C� � �C contacts are primarily the �-stacking interactions.

Special details
Experimental.The diffraction data were obtained from 3 sets of 400 frames, each of width 0.5° in ω, collected at φ = 0.00, 90.00 and 180.00° and 2 sets of 800 frames, each of width 0.45° in φ, collected at ω = -30.00and 210.00°.The scan time was 20 sec/frame.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.H-atoms attached to carbon were placed in calculated positions (C-H = 0.95 -0.99 Å).All were included as riding contributions with isotropic displacement parameters 1.2 -1.5 times those of the attached atoms.

Figure 4
Figure 4Packing viewed along the a-axis direction with C-H� � �O hydrogen bonds shown as black dashed lines and �-stacking and C-H� � ��(ring) interactions shown as orange and green dashed lines, respectively.

Figure 5
Figure 5Search fragment used in the database survey.

Figure 6 The
Figure 6The Hirshfeld surface plotted over d norm showing the C-H� � �O hydrogen bonds to neighboring molecules.

Figure 7 The
Figure 7The Hirshfeld surface plotted over shape-index showing the �-stacking and C-H� � ��(ring) interactions to neighboring molecules.

Table 2
Experimental details.