Crystal structure of 2-oxo-2H-chromen-3-yl propanoate

In the title compound, C12H9O4, the dihedral angle between the coumarin ring system and the propionate side chain is 78.48 (8)°.


Chemical context
Coumarin and its derivatives are widely recognized for their multiple biological activities, including anticancer (Lacy et al., 2004;Kostova, 2005), anti-inflammatory (Todeschini et al., 1998), antiviral (Borges et al., 2005), antimalarial (Agarwal et al., 2005) and anticoagulant (Maurer et al., 1998) properties. As part of our studies in this area, we now describe the synthesis and crystal structure of the title compound, (I).

Structural commentary
In compound (I) (Fig. 1), the coumarin ring system is almost planar [maximum deviation = 0.033 (1)Å ] and is oriented at an angle of 70.84 (8) with respect to the plane formed by the The molecular structure of compound (I), with displacement ellipsoids drawn at the 50% probability level.
propanoate group. An inspection of the bond lengths shows that there is a slight asymmetry of the electronic distribution around the coumarin ring: the C2-C3 [1.329 (2) Å ] and C2-C1 [1.460 (2) Å ] bond lengths are shorter and longer, respectively, than those expected for a C ar -C ar bond. This suggests that the electron density is preferentially located in the C2-C3 bond at the pyrone ring, as seen in other coumarin-3-carboxamide derivatives (Gomes et al., 2016).

Figure 3
A view of the crystal packing, showing thestacking and C-HÁ Á Á interactions (dashed lines). The green dots are ring centroids. H atoms not involved in the C-HÁ Á Á interactions have been omitted for clarity. Table 1 Hydrogen-bond geometry (Å , ).

Figure 4
Part of the crystal structure of (I), showing C-HÁ Á Á andinteractions as dashed lines. H atoms have been omitted for clarity.

Theoretical calculations
Quantum-chemical calculations were performed to compare with the experimental analysis. An ab-initio Hartree-Fock (HF) method was used with the standard basis set of 6-31G using the GAUSSIAN03 software package (Frisch et al., 2004;Dennington et al., 2007) to obtain the optimized molecular structure. The computational results are in good agreement with the experimental crystallographic data (Table 2).

Synthesis and crystallization
In a 100 ml round-necked flask topped with a water condenser were introduced successively 25 ml of dried diethyl ether, 6.17 Â 10 À3 mol (' 0.8 ml) of propionic anhydride and 2.35 ml (4.7 molar equivalents) of dried pyridine. While stirring strongly, 6.17 Â 10 À3 mol (1 g) of 3-hydroxycoumarin was added in small portions over 30 min. The reaction mixture was left under agitation at room temperature for 3 h. The mixture was then poured in a separating funnel containing 40 ml of chloroform and washed with diluted hydrochloric acid solution until the pH was 2-3. The organic layer was extracted, washed with water to neutrality, dried over MgSO 4 and the solvent removed. The resulting precipitate (crude product) was filtered off with petroleum ether and recrystallized from a solvent mixture of chloroform-hexane (1/3, v/v). Colourless prisms of the title compound were obtained in a yield of 65%, m. p. = 351-353 K.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3     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.