Crystal structure of 2-(4-chlorophenyl)-2-oxoethyl 3-bromobenzoate

Packing in the title keto ester compound is dominated by the formation of inversion dimers by both non-classical hydrogen bonds and offset π–π stacking interactions.

2-(4-Chlorophenyl)-2-oxoethyl 3-bromobenzoate, C 15 H 10 BrClO 3 , was synthesized in a single-step reaction by condensation of 3-bromobenzoic acid with 2-bromo-1-(4-chlorophenyl)ethanone in dimethylformamide in the presence of triethylamine as a catalyst. The structure consists of an aryl ketone moiety linked to an aryl ester unit by a methylene group. Both units are reasonably planar (r.m.s. deviations of 0.119 and 0.010 Å for the aryl ketone and aryl ester units, respectively) and are almost orthogonal, with an angle of 88.60 (3) between them. In the crystal, molecules form five separate sets of inversion dimers. Three of these are generated by two C-HÁ Á ÁO interactions and a C-HÁ Á ÁBr contact, and form chains along c and along the ab cell diagonal. In addition, two inversion-relatedstacking interactions between like aryl rings again form chains of molecules but in this instance along the bc diagonal. These contacts generate infinite layers of molecules parallel to (011) and stack the molecules along the a-axis direction.

Chemical context
Keto esters, an important class of versatile intermediates, have been reported to show antitumor activity against Ehrlich cells and HeLa cells (Kinoshita & Umezawa, 1960). They also regulate the flowering times of some plants (Kai et al., 2007). Recent studies have revealed that they also exhibit inhibitory activity against two isozymes of 11-hydroxysteroid dehydrogenases (11-HSD1 and 11-HSD2), which catalyse the interconversion of active cortisol and inactive cortisone (Zhang et al., 2009). Dicarbonyl compounds and their derivatives are also among the most versatile and frequently employed synthons in organic synthesis, especially in heterocyclic chemistry (Stanovnik & Svete, 2004;Sheibani et al., 2006aSheibani et al., ,b, 2007Pal et al., 2008). In this work, we report the synthesis of 2-(4-chlorophenyl)-2-oxoethyl 3-bromobenzoate, (1), which may be used as an effective synthon in organic chemistry.
groupings are reasonably planar. There is an r.m.s. deviation of 0.119 Å from the best-fit plane through atoms Br1, C1-C8, O1, O2 [maximum deviation 0.2477 (11) Å for O1] while the plane of the carboxylate unit subtends an angle of 15.5 (2) to that of the bromobenzene ring. In addition, the plane of the aryl ketone unit C8-C15, O3, Cl1 has an r.m.s. deviation of 0.010 Å [maximum deviation 0.0171 (15) Å for C15]. The aryl ketone and aryl ester planes are almost orthogonal with an angle of 88.61 (3) between them. Bond lengths and angles in the molecule are normal and are generally similar to those found in closely related molecules (see for example Fun et al., 2011a;Chidan Kumar et al., 2014c).

Figure 1
Fig, 1. The structure of (1) with displacement ellipsoids drawn at the 50% probability level.

Figure 2
Chains of linked inversion dimers generated by C-HÁ Á ÁO and C-HÁ Á ÁBr hydrogen bonds, drawn as dashed lines.

Figure 3
A chain of inversion dimers generated bycontacts, dotted green lines, between 3-bromophenyl and 4-chlorophenyl rings. Ring centroids are displayed as coloured spheres.

Synthesis and crystallization
The preparation followed a procedure developed for the preparation of a related compound (Khan et al., 2012). Triethylamine (4-5 drops) was added at room temperature to a stirred solution of 3-bromobenzoic acid (1.0 mmol) in N,N-dimethylformamide (DMF), followed by a solution of 2-bromo-1-(4-chlorophenyl)ethanone (1.0 mmol). The reaction mixture was stirred for 2 h. Progress of the reaction was monitored by TLC. After completion, the mixture was poured into water and the precipitated solid was filtered, dried and recrystallized (EtOAc/hexane) to afford 2-(4-chlorophenyl)-2oxoethyl 3-bromobenzoate (1). The formation of keto ester (3) was indicated by the appearance of two typical stretching vibrations (C=O) ester (1724) and (C=O) keto (1698) cm À1 , respectively and the disappearance of characteristic IR stretching absorptions ascribable to the carboxylic acid group in the region of 3400-2400 cm À1 . In the 1 H NMR spectrum, the signals for the aromatic protons appeared in their respective regions and the disappearance of a characteristic signal for the COOH proton confirmed the formation of the title compound (1).

Refinement
All H atoms were refined using a riding model, with C-H = 0.95 Å and U iso (H) = 1.2U eq (C) for aromatic, and C-H = 0.99 Å and U iso (H) = 1.2U eq (C) for the methylene H atoms.

Special details
Experimental. Absorption correction: CrysAlisPro, Agilent (2011), Empirical absorption correction using spherical harmonics, implemented in SCALE3 ABSPACK scaling algorithm. 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.