Crystal structure of ethyl 6-bromo-2-[(E)-2-phenylethenyl]quinoline-4-carboxylate

In the title compound, C20H16BrNO2, the dihedral angle between the quinolone ring system mean plane (r.m.s. deviation = 0.018 Å) and the phenyl ring bridged by the ethynyl group, is 25.44 (14)°. There is an intramolecular C—H⋯O hydrogen bond forming an S(6) ring motif. In the crystal, molecules are linked via C—H⋯O hydrogen bonds forming chains propagating along the b-axis direction.


S1. Comment
Quinolines have been considered as the most prevalent N-hetero aromatic compounds that exhibit a wide spectrum of pharmaceutical and pharmacological activities (Beagley et al., 2003). Some of the quinoline-4-carboxylates were reported to possess potent 5HT 3 antagonizing activity and anti-emetic activity. In view of their broad spectrum of medicinal properties and in continuation of our work on new quinoline based therapeutic agents (Pradeep et al., 2014), the title compound was synthesized, and we report herein on its crystal structure.
The molecular structure of the title molecule is shown in Fig In the crystal, molecules are linked via C-H···O hydrogen bonds forming chains propagating along the b axis direction (Table 1 and Fig. 2).

S2. Experimental
A mixture of 2-aryl-6-chloro/bromo quinoline-4-carboxylic acid (1.0 g) and absolute EtOH (15 ml) was stirred at 273 -278 K. The concentrated sulfuric acid (2 -3 ml) was added drop wise into the flask until the powdered 2-aryl-6-chloroquinoline-4-carboxylic acid was completely dissolved. The solution was then refluxed for 15-17 h. The completion of the reaction was monitored by thin layer chromatography [hexane and ethyl acetate (9:1 v/v)]. The reaction mixture was poured into a crushed ice (100 ml), the precipitate was collected by filtration, washed with water and EtOH, dried under vacuum to afford crude product. The crude product was purified by column chromatography using silica gel (60-120 mesh, petroleum ether: ethyl acetate, 9:1 v/v). Green block-shaped crystals were obtained by slow evaporation of the solvent.

S3. Refinement
All the H atoms were fixed geometrically (C-H = 0.93-0.96 Å and allowed to ride on their parent atoms with U iso (H) = 1.5U eq (C) for methyl H atoms and = 1.2U eq (C) for other H atoms.

Figure 1
A view of molecular structure of the title compound, with atom labelling. Displacement ellipsoids are drawn at the 50% probability level. The intramolecular hydrogen bond is shown as dashed line (see Table 1 for details).

Figure 2
A partial view along the a axis of the crystal packing of the title compound. The intra-and inter-molecular hydrogen bonds are shown as dashed lines (see Table 1 for details; H atoms: grey balls; H atoms not involved in hydrogen bonding have been omitted for clarity). where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 0.78 e Å −3 Δρ min = −0.92 e Å −3 Special details Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell e.s.d.'s are taken into account in the estimation of distances, angles and torsion angles Refinement. Refinement on F 2 for ALL reflections except those flagged by the user for potential systematic errors. Weighted R-factors wR and all goodnesses 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 observed criterion of F 2 > σ(F 2 ) is used only for calculating -R-factor-obs 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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq