Crystal structure, Hirshfeld surface analysis and density functional theory study of benzyl 2-oxo-1-(prop-2-yn-1-yl)-1,2-dihydroquinoline-4-carboxylate

The molecule adopts a Z-shaped conformation with the carboxyl group nearly coplanar with the dihydroquinoline unit. In the crystal, two sets of C—H⋯O hydrogen bonds form chains along the b-axis direction, which are connected into corrugated layers parallel to (103) by additional C—H⋯O hydrogen bonds. The layers are connected by C—H⋯π(ring) interactions.


Chemical context
Nitrogen-based structures have attracted increased attention in recent years because of their interesting properties in structural and inorganic chemistry (Chkirate et al., 2019(Chkirate et al., , 2020a(Chkirate et al., ,b, 2021. The family of quinolines, particularly those containing the 2-oxoquinoline moiety, is important in medicinal chemistry because of their wide range of pharmacological applications including as potential anticancer agents (Fang et al., 2021), anti-proliferative agents (Banu et al., 2017) and as potent modulators of ABCB1-related drug resistance of mouse T-lymphoma cells (Filali Baba et al., 2020). In particular, 2-oxoquinoline-4-carboxylate derivatives are active antioxidants (Filali Baba et al., 2019). Given the wide range of therapeutic applications for such compounds, and in a continuation of the work already carried out on the synthesis of compounds resulting from quinolin-2-one (Bouzian et al., 2020), a similar approach gave the title compound, benzyl 2-oxo-1-(prop-2-yn-1-yl)-1,2-dihydroquinoline-4-carboxylate, (I). Besides the synthesis, we also report the molecular and crystalline structures along with a Hirshfeld surface analysis and a density functional theory computational calculation carried out at the B3LYP/6-311 G(d,p) level. ISSN 2056-9890

Structural commentary
The molecule adopts a Z-shaped conformation with the propynyl and benzyl substituents projecting from opposite sides of the mean plane of the dihydroquinoline moiety. This moiety is planar to within 0.0340 (6) Å (r.m.s. deviation = 0.0164) with N1 and C9 being, respectively, 0.0340 (6) and À0.0279 (7) Å from the mean plane, resulting in a slight twist at this location. The carboxyl group is nearly coplanar with the dihydroquinoline as seen from the 1.04 (5) dihedral angle between the plane defined by C7/C13/O2/O3 and that of the dihydroquinoline (C1-C9/N1/O1). This is likely due, in part, to the intramolecular C5-H5Á Á ÁO2 interaction (Table 1 and Fig. 1). The propynyl substituent is rotated out of the mean plane of the dihydroquinoline moiety by 80.88 (3) . The plane of the C15-C20 ring is inclined to that of the dihydroquinoline by 68.47 (2) .

Hirshfeld surface analysis
The CrystalExplorer program (Turner et al., 2017) was used to investigate and visualize further the intermolecular interactions of (I). The Hirshfeld surface plotted over d norm in the range À0.3677 to 1.3896 a.u. is shown in Fig. 4a. The electrostatic potential using the STO-3G basis set at the Hartree-Fock level of theory and mapped on the Hirshfeld surface over the range of AE0.05 a.u. clearly shows the positions of close intermolecular contacts in the compound (Fig. 4b) Table 1 Hydrogen-bond geometry (Å , ).

Figure 2
A portion of one layer viewed along the c axis with C-HÁ Á ÁO hydrogen bonds depicted by dashed lines.

Figure 3
Packing viewed parallel to (103) with the b axis horizontal and running from left to right. C-HÁ Á ÁO hydrogen bonds and C-HÁ Á Á(ring) interactions are depicted, respectively, by black and green dashed lines.

Figure 1
The title molecule with labeling scheme and 50% probability ellipsoids. The intramolecular hydrogen bond is depicted by a dashed line.

Density Functional Theory calculations
The structure in the gas phase of the title compound was optimized by means of density functional theory. The density functional theory calculation was performed by the hybrid B3LYP method and the 6-311 G(d,p) basis-set, which is based on Becke's model (Becke, 1993) and considers a mixture of the exact (Hartree-Fock) and density functional theory exchange utilizing the B3 functional, together with the LYP correlation functional (Lee et al., 1988). After obtaining the converged geometry, the harmonic vibrational frequencies were calculated at the same theoretical level to confirm that the number of imaginary frequencies is zero for the stationary point. Both the geometry optimization and harmonic vibrational frequency analysis of the title compound were performed with the Gaussian 09 program (Frisch et al., 2009). Theoretical and experimental results related to bond lengths and angles are in good agreement, and are summarized in Table 2    View of the three-dimensional Hirshfeld surface of the title compound plotted over electrostatic potential energy in the range À0.0500 to 0.0500 a.u. using the STO-3 G basis set at the Hartree-Fock level of theory. potential (I), dipole moment (), electron affinity (A), electrophilicity (!) and softness () are collated in Table 3. The electron transition from the highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO) energy level is shown in Fig. 6. The HOMO and LUMO are localized in the plane extending over the whole benzyl 2-oxo-1-(prop-2-yn-1-yl)-1,2-dihydroquinoline-4-carboxylate system. The energy band gap (ÁE = E LUMO À E HOMO ) of the molecule is 4.0319 eV, and the frontier molecular orbital energies, E HOMO and E LUMO , are À6.3166 and À2.2847 eV, respectively.

Database survey
A search of the Cambridge Structural Database (CSD version 5.42, updated May 2021;Groom et al., 2016) with the 2-oxo-1-(prop-2-yn-1-yl)-1,2-dihydroquinoline-4-carboxylate fragment yielded multiple matches. Of these, two had an alkyl substituent on O3 comparable to (I). The first compound (refcode OKIGAT; Hayani et al., 2021) carries an ethyl group on O3, while the second one (refcode OKIGOH; Hayani et al., 2021) carries a cyclohexyl group. The ethyl carboxylate in OKIGAT forms a dihedral angle of À8.3 (7) with the dihydroquinoline unit. In OKIGOH, the dihedral angle between the mean planes of the cyclohexyl carboxylate and dihydroquinoline rings is 37.3 (8) . As previously mentioned, the carboxyl group in (I) is nearly coplanar with the dihydroquinoline [dihedral angle of 1.04 (5) ], which is approximately the same as in OKIGAT, but less tilted than in OKIGOH.

Synthesis and crystallization
A mixture of 2-oxo-1-(prop-2-yn-1-yl)-1,2-dihydroquinoline-4-carboxylic acid (0.7 g, 3 mmol), K 2 CO 3 (0.51 g, 3.6 mmol), benzyl chloride (0.76 ml, 6 mmol) and tetra n-butylammonium bromide as a catalyst in DMF (30 mL) was stirred at room temperature for 48 h. After removal of the salts by filtration, the solvent was evaporated under reduced pressure and the residue obtained was dissolved in dichloromethane. The organic phase was dried over Na 2 SO 4 and concentrated under vacuum. The crude product obtained was purified by chro-

Table 2
Comparison (X-ray and DFT) of selected bond lengths and angles (Å , ).

Special details
Experimental. The diffraction data were obtained from 9 sets of frames, each of width 0.5° in ω or φ, collected with scan parameters determined by the "strategy" routine in APEX3. The scan time was 7 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 -1.00 Å). All were included as riding contributions with isotropic displacement parameters 1.2 -1.5 times those of the attached atoms. Two reflections affected by the beamstop were omitted from the final refinement.