2-Oxo-2 H-chromen-3-yl 4-tert-butylbenzoate

In the title coumarin derivative, C20H18O4, the benzene ring of the benzoate group is oriented at a dihedral angle of 57.55 (9) with respect to the planar chromene ring system [maximum deviation from plane is 0.027 (2) Å]. In the crystal, inversion-related molecules are linked into dimers via C—H O hydrogen bonds, generating R2 (12) loops. The dimers are linked by further C— H O hydrogen bonds forming layers, parallel to the bc plane, which are linked via C—H interactions, forming a three-dimensional framework

In the title coumarin derivative, C 20 H 18 O 4 , the benzene ring of the benzoate group is oriented at a dihedral angle of 57.55 (9) with respect to the planar chromene ring system [maximum deviation from plane is 0.027 (2) Å ]. In the crystal, inversion-related molecules are linked into dimers via C-HÁ Á ÁO hydrogen bonds, generating R 2 2 (12) loops. The dimers are linked by further C-HÁ Á ÁO hydrogen bonds forming layers, parallel to the bc plane, which are linked via C-HÁ Á Á interactions, forming a three-dimensional framework

Structure description
Coumarins are bioactive substances of the benzo--pyrone family and are of great interest due to their pharmacological properties, showing antioxidant, antiviral and antiinflammatory effects, among others (Francisco et al., 2016). In particular, the physiological, bacteriostatic and anti-tumor activities make these compounds attractive for backbone derivatization and screening as novel therapeutic agents (Jain et al.,2012). They possess a conjugated system with good charge-transport properties (Murray et al.,1982). Coumarins have a sweet odor, easily recognized by the scent of new-mown hay, and hence they have been used in perfumes since 1882. It is presumed to be produced by plants as a chemical defense to discourage predation. In another important application, coumarin dyes are extensively used as gain media in blue-green tunable organic dye lasers (Schä fer, 1990;Duarte & Hillman, 1990;Duarte, 2003). They are also used as the active medium in coherent OLED emitters (Duarte et al., 2005). As part of our ongoing studies in this area, we now describe the synthesis and the crystal structure of the title coumarin derivative which has a benzoate substituent at position 3 of the coumarin ring data reports system (Fig. 1). Our group has previously reported a number of related structures (Abou et al., 2011, 2012a,b, Abou et al., 2013. In the title compound, Fig. 1, the benzene ring is inclined to the coumarin ring by 57.55 (9) . The bond lengths and angles in the title molecule are similar to those observed for the 4methylbenzoate analogue, 2-oxo-2H-chromen-3-yl 4-methylbenzoate (Matos et al., 2013). There, however, the benzene ring is inclined to the coumarin ring by 79.64 (5) .
In the crystal, molecules are linked by pairs of C6-H6Á Á ÁO4 ii hydrogen bonds, forming inversion dimers that generate R 2 2 (12) ring motifs (Table 1 and Fig. 2). The dimers are linked by further C-HÁ Á ÁO hydrogen bonds, forming layers parallel to the bc plane (Table 1). The layers are linked via C-HÁ Á Á interactions, forming a three-dimensional framework (Table 1).

Synthesis and crystallization
Dried triethylamine (3 mol) was add to a solution of 4-tertbutylbenzoyl chloride (6.17 10 À3 mol) in dried tetrahydrofuran (31 ml). While stirring vigorously, 6.17 10 À3 mol of chroman-2,3-dione was added in small portions over 30 min. The reaction mixture was then refluxed for 4 h and poured in a separatory funnel containing 40 ml of chloroform. The solution was acidified with dilute hydrochloric acid until the pH changed to 2-3. The organic layer was extracted, washed with water until neutral, dried over MgSO 4 and the solvent removed in vacuo. The resulting precipitate (crude product) was filtered off with suction, washed with petroleum ether and dissolved in a minimum of chloroform by heating under agitation. Hexane was added to this hot mixture until the formation of a new precipitate started, which dissolved in the resulting mixture upon heating. While cooling, colourless Table 1 Hydrogen-bond geometry (Å , ).

Figure 1
The molecular structure of the title compound, with atom labelling. Displacement ellipsoids are drawn at the 30% probability level.
crystals of the title compound suitable for X-ray diffraction analysis were formed (yield of 84%, m.p. 413-410 K).

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2.

data-1
IUCrData ( Special details 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.