4-Oxo-2-phenylchroman-6-yl propionate

In the structure of the title compound, C18H16O4, both the S and R enantiomers appear to occupy in a random way four symmetry-equivalent sites of the unit cell in an approximately 4:1/1:4 ratio. The chiral C atom of the pyrone ring together with the phenyl ring bonded to this atom are disordered over two positions, the occupancy factor of the major component being 0.809 (5). Adjacent molecules are linked by weak C—H⋯O hydrogen bonds.

In the structure of the title compound, C 18 H 16 O 4 , both the S and R enantiomers appear to occupy in a random way four symmetry-equivalent sites of the unit cell in an approximately 4:1/1:4 ratio. The chiral C atom of the pyrone ring together with the phenyl ring bonded to this atom are disordered over two positions, the occupancy factor of the major component being 0.809 (5). Adjacent molecules are linked by weak C-HÁ Á ÁO hydrogen bonds.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: HG2666). range of valuable biological activities of these compounds. These include antiallergic, antiatherogenic, antidiabetic, antidiarrheic, antiinflammatory, antihepatotoxic and anticancerogenic properties [Di Carlo et al., 1999;Rice-Evans, 2004;Wang, 2000]. The wide spectrum of their pharmacological activities depends on chemical structures. Especially important is presence of carbonyl group, as well as presence, number and location of hydroxyl groups. For example, the presence of hydroxyl groups in the B ring is the main factor determining antioxidant activity of flavonoids [Halliwell, 1996;Rice-Evans et al., 1996].
Transformation of flavonoids by means of microorganisms is a way of modification of their structure, as well as a helpful tool for elucidation of their metabolism in mammals [Kostrzewa-Susłow et al., 2008].
The crystal structure of 6-propionoxyflavanone, together with numbering scheme employed, is presented in Fig. 1 The C11-C16 (or C11A-C16A) phenyl ring is oriented almost perpendicular to the plane of the C5-C10 arene ring. The angle between the plane of the C11-C16 (C11A-C16A) ring and the plane of the C5-C10 ring is equal to 79.79 (12) °( 89.8 (5) °). The angle between the plane of carboxylate group and the plane of the C5-C10 ring is equal to 75.62 (8) °.
The O1, C3, C4 O17 atoms are situated approximately in the plane of the C5-C10 arene ring (maximum deviation is equal to 0.040 (3) Å for O1). While deviation of the C18 and C2 atoms from the plane formed by the C5-C10 arene ring are equal to 1.140 (4) and 0.676 (4) Å, respectively, deviation of the C2A atom from the plane is equal to -0.403 (13) Å. Thus, two enantiomers revealing various conformations occupy equivalent sites, however somewhat randomly, not systematically, arranged in the unit cell. The ratio of the two enantiomers (R:S) in an asymmetric part of the unit cell is approximately equal to 0.8:0.2, which gives a 4:1/1:4 ratio in the crystal structure overall.

Experimental
The title compound was obtained during esterification of 6-hydroksyflavanone using propionyl chloride (Fig.2). Crystals of 6-propionoxyflavanone were grown from a THF (tetrahydrofurane) solution under ambient conditions. supplementary materials sup-2 Refinement Occupancy factors for C2, C2A, C11-C16 and C11A-C16A were refined. The C11A-C16A atoms were refined using ISOR restrain. All H atoms were placed at calculated positions. H atoms attached to carbons were constrained as riding atoms, with C-H set to 0.95 -0.99 Å. U iso (H) values were set to 1.2U eq of the parent atom.

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.
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 Rfactors(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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Occ. (