Crystal structure of ethyl 2-chloro-6-methylquinoline-3-carboxylate

In the title compound, C13H12ClNO2, the dihedral angle between the planes of the quinoline ring system (r.m.s. deviation = 0.029 Å) and the ester group is 54.97 (6)°. The C—O—C—Cm (m = methyl) torsion angle is −140.62 (16)°. In the crystal, molecules interact via aromatic π–π stacking [shortest centroid–centroid separation = 3.6774 (9) Å] generating (010) sheets.


S1. Comment
The 2-chloro-3-formylquinolines occupy a prominent position as key intermediates for further annelation and various functional group inter-conversions (Abdel-Wahab et al., 2012;Michael, 2004). As part of our ongoing studies in this area (Benzerka et al., 2012(Benzerka et al., , 2013, we now describe the synthesis and single-crystal X-ray structure of the title compound, (I).
The molecular geometry and the atom-numbering scheme of (I) are shown in Fig. 1. In the asymmetric unit of title compound the quinoline ring is three times substituted by two methyl, one chlore and one ethyl carboxylate. The crystal packing can be described as double layers parallel to (010) plane (Fig. 2). It features π···π stacking, distances controidcontroid between aromatic rings are from 3.6774 (9) to 4.2262 (9) Å.

S2. Experimental
Into a solution of NaCN (3 mmol) in absolute ethanol (15 ml), was added, in portion and at 0 °C,a mixture of 1 mmol of 2-chloro-3-formyl-6-methylquinoline and activated manganese dioxide (6.7 mmol). The reaction mixture was stirred for 3 h at rt. Purification of the corresponding compound was carried out by diluting the reaction mixture with CH 2 Cl 2 and filtering through a small column packed with 4 cm of celite and 3 cm of silica gel. The pure compound was recovered after evaporation of solvents. Colourless blocks of (I) were obtained by dissolving the pure compound in EtOH and allowing the solution to slowly evaporate at room temperature.

S3. Refinement
All H atoms were localized on Fourier maps but introduced in calculated positions and treated as riding on their parent C atom. (with C-H = 0.93 (aromatic), 0.96 (methyl) and 0.97 Å (methylene) and U iso (H) =1.5 or 1.2(carrier atom).

Figure 1
The structure of the title compound with displacement ellipsoids drawn at the 50% probability level.

Figure 2
A diagram of the layered crystal packing of (I) viewed down the a axis.

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s 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 > σ(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.