Crystal structure and Hirshfeld surface analysis of 4-(3-methoxyphenyl)-2,6-diphenylpyridine

The title compound was obtained via the reaction of (1E,2E)-3-(3-methoxyphenyl)-1-phenylprop-2-en-1-one with ethyl 2-oxopropanoate, using NH4I as a catalyst. In the molecule, the four rings are not in the same plane, the pyridine ring being inclined to the benzene rings by 17.26 (6), 56.16 (3) and 24.50 (6)°. In the crystal, molecules are linked by C—H⋯π interactions into a three-dimensional network.


Chemical context
Substituted pyridines are privileged scaffolds in medicinal chemistry and are versatile building blocks for the construction of natural products (Haghighijoo et al., 2020;Gujjarappa et al., 2020;Nirogi et al., 2015;De Rycke et al., 2011;Chan et al., 2010;Bora et al., 2010), Accordingly, great effort has been devoted to developing efficient approaches to these scaffolds (Guin et al., 2020;Wu et al., 2019;Pandolfi et al., 2017;Shen et al., 2015). Ketoxime acetates have been demonstrated to be exceptionally advantaged and versatile building blocks for the synthesis and derivatization of nitrogen-containing heterocycles through N-O bond cleavage Mao et al., 2019;Xie et al., 2018). Thus far, many synthetic approaches have been developed to access nitrogen-containing heterocycles through ketoxime acetates under metal-free conditions. For example, Duan et al. (2020) have successfully developed the NH 4 I-triggered formal [4 + 2] annulation of ,-unsaturated ketoxime acetates with N-acetyl enamides, providing efficient access to valuable highly substituted pyridines in moderate to good yields. Gao et al. (2018) have developed a facile and efficient I 2 -triggered [3 + 2 + 1] annulation of aryl ketoxime acetates and 3-formylindoles to produce diverse 3-(4-pyridyl)indoles that are challenging to prepare by traditional methods. Given this background, we report herein the synthesis and crystal structure of the title compound, which was synthesized by NH 4 I-triggered annulation of ,-unsaturated ketoxime acetates.

Structural commentary
The title compound crystallizes in the monoclinic crystal system in space group I2/a. Its molecular structure is shown in Fig. 1. The methoxy group lies close to the mean plane of the C12-C17 phenyl ring, as indicated by the C17-C16-O1-C24 torsion angle of À170.59 (10) , and atom C24 deviating by 0.250 (2) Å from the mean plane through the C12-C17 ring. In the molecule, the four rings are not in the same plane, the pyridine ring being inclined to the C6-C11, C12-C17 and C18-C23 benzene rings by 17.26 (6), 56.16 (3) and 24.50 (6) , respectively. There is a strong intramolecular hydrogen bond (C7-H7Á Á ÁN1; Table 1), forming an S(5) ring motif.

Supramolecular features
In the crystal (Fig. 2), the molecules are linked by weak C-HÁ Á Á interactions (C14-H14Á Á ÁCg2 i and C24-H24Á Á ÁCg3 ii , Cg2 and Cg3 are the centroids of the C6-C11 and C12-C17 rings, respectively, symmetry codes as in Table 1). The C24-H24Á Á ÁCg3 interactions generate stacks along the b-axis direction. These stacks are linked by the C14-H14Á Á ÁCg2 interactions. The packing is strengthened by van der Waals interactions between parallel molecular layers.
In order to investigate the intermolecular interactions in a visual manner, a Hirshfeld surface analysis was performed using Crystal Explorer (Spackman & Jayatilaka, 2009;Turner et al., 2017). Fig. 3 shows the d norm surface together with two adjacent molecules. The bright-red spots on the Hirshfeld surface mapped over d norm correspond to H24BÁ Á ÁH20 (x À 1 2 , 2 À y, z) close contacts.   Table 1 Hydrogen-bond geometry (Å , ).

Figure 2
A packing diagram of the title compound. The C-HÁ Á Á interactions are shown as dashed lines. Yellow spheres denoted Cg represent the centroids of the 3-methoxyphenyl rings.

Figure 1
The molecular structure of the title compound, with the atom labelling and displacement ellipsoids drawn at the 50% probability level. H atoms are shown as small circles of arbitrary radii.

Synthesis and crystallization
15 mmol) and NaHSO 3 (0.31 g, 3.0 mmol) were loaded into a 20 mL tube under an N 2 atmosphere. The solvent toluene (15 mL) was added into the tube by syringe. The reaction mixture was stirred at 373 K for 12 h. Upon completion of the reaction, the mixture was then allowed to cool down to room temperature and flushed through a short column of silica gel with EtOAc (15 mL). After rotary evaporation, the residue was purified by column chromatography on silica gel (petroleum ether/EtOAc) to give the product as a white solid. Part of the purified product was redissolved in petroleum ether/ethyl acetate and colourless crystals suitable for X-ray diffraction were formed after slow evaporation for several days.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. All H atoms were positioned geometrically with C-H = 0.93-0.98 Å and refined as riding atoms. The constraint U iso (H) = 1.2U eq (C) or 1.5U eq (C Me ) was applied in all cases.

Funding information
We

Figure 3
The Hirshfeld surface mapped over d norm together with two adjacent molecules.  software used to prepare material for publication: OLEX2 (Dolomanov et al., 2009).  (9) 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.