Diethyl 4-oxo-4H-[1,4′-biquinoline]-3,3′-dicarboxylate

In the title molecule, C24H20N2O5, the quinoline and quinolinone moieties are practically perpendicular to each other, forming a dihedral angle of 89.06 (3)°. In the crystal, each moiety forms coplanar π-stacked couples with the respective inversion equivalents. The quinolinone moieties overlap with their benzene rings with a centroid–centroid separation of 3.641 (2) Å, whereas the quinoline moieties overlap with their pyridine rings with a separation of 3.592 (2) Å. The resulting supramolecular chains propargate along [101].

In the title molecule, C 24 H 20 N 2 O 5 , the quinoline and quinolinone moieties are practically perpendicular to each other, forming a dihedral angle of 89.06 (3) . In the crystal, each moiety forms coplanar -stacked couples with the respective inversion equivalents. The quinolinone moieties overlap with their benzene rings with a centroid-centroid separation of 3.641 (2) Å , whereas the quinoline moieties overlap with their pyridine rings with a separation of 3.592 (2) Å . The resulting supramolecular chains propargate along [101].

Related literature
For the background to this study, see: Ishikawa & Fujii (2011). For a related compound, see: Kajihara (1965). This work was partly supported by Grants-in-Aid (No. 24590141 to YI) for Scientific Research from the Japan Society for the Promotion of Science. We acknowledge the University of Shizuoka for instrumental support, and thank Professor Kei Manabe (University of Shizuoka, Japan) for helpful discussions.

Comment
4-Quinolones show inhibition not only to Gram-negative and Gram-positive bacteria, but also to human immunodeficiency virus (HIV). The inhibition to HIV is derived from their chelating ability to metal ions in the active site of the metalloenzyme HIV integrase. According to our inhibitor design targeting the metalloenzyme influenza virus RNA polymerase (Ishikawa & Fujii, 2011), we tried to synthesize a 4-quinolone derivative bearing a benzensulfonyl group. Reaction of ethyl 4-oxo-1,4-dihydroquinoline-3-carboxylate with benzenesulfonyl chloride in the presence of K 2 CO 3 in N,N-dimethylformamide (DMF) at 120 °C gave the white solid after purification by silica gel chromatography ( Fig.1).
The crystallographic analysis revealed that it is a self-condensation product of ethyl 4-oxo-1,4-dihydroquinoline-3carboxylate with a loss of one water molecule, as shown in Fig.2. This structure well accounts for the 1 H NMR and MS spectra. The C-N bond formation should occur via the formation of a benzenesulfonate intermediate. The quinoline rings are approximately perpendicular to each other [dihedral angle = 90.94 (3)°]. In the crystal, the molecule is assembled via stacking interaction with its inversion equivalents i,ii [centroid-centroid distances between the benzene rings of the upper quinoline units = 3.641 (2) Å (i: -x, -y, -z) and between the pyridine rings of the lower quinoline units = 3.592 (2) Å (ii: -x + 1, -y, -z + 1)]. As a result, the molecules form chains along [101] direction, as shown in Fig.3. Report on the synthesis of 1,4′-quinolines is scarce (Kajihara, 1965).

Experimental
In a Schlenk tube under nitrogen atmosphere, the mixture of ethyl 4-oxo-1,4-dihydroquinoline-3-carboxylate (0.20 g, 1.0 mmol), benzenesufonyl chloride (0.35 g, 2.0 mmol), K 2 CO 3 (0.28 g, 2.0 mmol) in 5 ml of DMF were stirred at 120 °C overnight. After cooling to room temperature water was added, and the mixture was extracted with ethyl acetate three times. The extract was dried over anhydrous Na 2 SO 4 , and purified by column chromatography on silica gel (ethyl acetate:   Reaction scheme for the title compound.

Figure 2
The molecular structure of the title compound, with displacement ellipsoids drawn at the 50% probability level.
Hydrogen atoms are shown as small spheres of arbitrary radius.

Data collection
Rigaku AFC-7R diffractometer ω-2θ scans 5486 measured reflections 4479 independent reflections 3077 reflections with F 2 > 2σ(F 2 ) R int = 0.034 Special details Refinement. Refinement was performed using all reflections. The weighted R-factor (wR) and goodness of fit (S) are based on F 2 . R-factor (gt) are based on F. The threshold expression of F 2 > 2.0 σ(F 2 ) is used only for calculating R-factor (gt).