Crystal structure and Hirshfeld surface analysis of phenyl(5,7,8a-triphenyl-1,2,3,7,8,8a-hexahydroimidazo[1,2-a]pyridin-6-yl)methanone with an unknown solvent

The crystal exhibits weak intramolecular π–π interactions between the phenyl rings. In the crystal, molecules are linked via pairs of C—H⋯ O, forming inversion dimers. The dimers are further linked by pairs of C—H⋯π interactions, forming infinite chains along the c-axis direction.

In the title compound, C 32 H 28 N 2 O, the imidazolidine and pyridine rings of the central hexahydroimidazo[1,2-a]pyridine ring system adopt envelope and screwboat conformations, respectively. The molecule exhibits two weak intramolecularinteractions between phenyl rings. In the crystal, molecules are linked via pairs of C-HÁ Á Á O hydrogen bonds, forming inversion dimers. The dimers are further linked by pairs of C-HÁ Á Á interactions, forming infinite chains along the c-axis direction. A Hirshfeld surface analysis indicates that the most important contributions to the crystal packing are from HÁ Á ÁH (73.4%), CÁ Á ÁH/HÁ Á ÁC (18.8%) and OÁ Á ÁH/HÁ Á ÁO (5.7%) contacts. The contribution of some disordered solvent to the scattering was removed using the SQUEEZE routine [Spek (2015). Acta Cryst. C71, 9-18] in PLATON. The solvent contribution was not included in the reported molecular weight and density.

Chemical context
Carbon-carbon and carbon-heteroatom bond-forming reactions are the most powerful and fundamental tools in synthetic organic chemistry. These synthetic approaches have successfully found applications in the construction of carbo-and heterocyclic ring systems (Khalilov et al., 2011;Yin et al., 2020). The use of nitrogen as the bridgehead atom is being assessed extensively. Bridgehead nitrogen heterocycles comprising imidazole rings are prevalent structural motifs in many compounds having applications in medicinal chemistry, coordination chemistry and material science (Afkhami et al., 2017;Mahmoudi et al., 2017a,b;Mahmudov et al., 2019Mahmudov et al., , 2020. Various imidazo[1,2-a]pyridine moieties are included in synthetic drugs, such as alpidem, olprinone, saripidem, necopidem, miroprofen, zolimidine and zolpidem, which have already found use in medicinal practice. On the other hand, the imidazo[1,2-a]pyridine motif is also found in a series of natural products, such as oxaline and neoxaline (Koizumi et al., 2004). As a result of the considerable interest to this field, there have been significant developments in the synthesis of imidazo[1,2-a]pyridine derivatives. In the framework of our ongoing structural studies (Akkurt et al., 2018;Khalilov et al., 2019), we report herein the crystal structure and Hirshfeld surface analysis of the title compound.

Supramolecular features and Hirshfeld surface analysis
In the crystal, molecules are linked via pairs of C-HÁ Á Á O hydrogen bonds, forming inversion dimers. The dimers are further linked by pairs of C-HÁ Á Á interactions, forming an infinite chain along the c-axis direction (Table 1 and Fig. 2).
In order to obtain further insight into the intermolecular interactions, we used Crystal Explorer (Turner et al., 2017). The Hirshfeld surface of the title compound mapped over d norm is depicted in Fig. 3, where the red regions are apparent around atom O1, which participates in the C-HÁ Á ÁO interactions (Table 1). The fingerprint plots (Fig. 4)  The molecular structure of the title compound, with displacement ellipsoids drawn at the 30% probability level. Table 1 Hydrogen-bond geometry (Å , ).

Figure 2
The crystal packing of the title compound. Dashed lines indicate C-HÁ Á ÁO, C-HÁ Á Á andstacking interactions. Cg3, Cg4, Cg5 and Cg6 are the centroids of the C9-C14, C15-C20, C21-C26 and C27-C32 phenyl rings, respectively. [Symmetry codes: (a) Àx, Ày, Àz + 1; (b) Àx, Ày, Àz + 2.] largest contribution to the overall crystal packing is from HÁ Á ÁH contacts (73.4%). The second largest percentage (18.8%) can be attributed to CÁ Á ÁH/HÁ Á ÁC contacts, which correlate with the C-HÁ Á Á interactions. OÁ Á ÁH/HÁ Á ÁO contacts (5.7%), which correlate with the C-HÁ Á ÁO interactions, provide another significant contribution to the Hirshfeld surface. Other contributions include NÁ Á ÁH/HÁ Á ÁN (1.9%) and CÁ Á ÁC (0.2%). The removal of the contribution of the disordered solvent to the scattering using the SQUEEZE routine of PLATON may be responsible for a small change in the given percentage contributions.  Wireko et al., 1995). In KICJUE, single crystal X-ray analysis confirmed the trans derivative as the only isomer. The structure of TEZJOZ shows that the aromatic ring of the aldehyde is on the other plane of the ketone in the purposed mechanism for the reaction. In the crystal of YUYREP, each water molecule bridges two molecules of the compound, hydrogen bonding with the carbonyl O atom of one molecule [OÁ Á ÁOW = 2.796 (4) Å ] and with the N atom of the other [NÁ Á ÁOW = 2.903 (4) Å ]. The methyl group at the bridgehead is axially located in a trans position with respect to the bulky benzyloxy group. The pyridone ring assumes a slightly distorted half-chair conformation.

Synthesis and crystallization
To a solution of 2-benzoyl-1,3,5-triphenylpentane-1,5-dione (3.5 mmol) in ethanol (35 ml) was added ethylenediamine (3.7 mmol) and 5 drops of concentrated HCl. The mixture was stirred at room temperature for 15 min, then refluxed for 4 h and cooled down to room temperature. The reaction product precipitated from the reaction mixture as colourless single crystals, which were collected by filtration and purified by recrystallization from ethanol (yield 76%; m.p. 465-466 K).

Refinement details
Crystal data, data collection and structure refinement details are summarized in    0.908 (16) Å ]. The remaining H atoms were placed in calculated positions (C-H = 0.95-1.00 Å ) and allowed to ride on their carrier atoms, with U iso = 1.2U eq (C). The residual electron density was difficult to model and therefore the SQUEEZE routine (Spek, 2015) in PLATON (Spek, 2020) was used to remove the contribution of the electron density in the solvent region from the intensity data and the solvent-free model was employed for the final refinement. The solvent formula mass and unit-cell characteristics were not taken into account during refinement. The cavity of volume ca 119 Å 3 (ca 9.4% of the unit-cell volume) contains approximately 28 electrons.

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.