(3E,5E)-3,5-Bis(4-hydroxybenzylidene)oxan-4-one

In the title compound, C19H16O4, there are two 4-hydroxybenzyl substituents on the oxan-4-one (tetrahydropyran-4-one) ring, which exhibits an envelope conformation. The dihedral angles between pyranone ring and the two benzene rings are 26.69 (9) and 36.01 (9)° while the benzene rings make a dihedral angle of 20.88 (10)°. In the crystal, molecules are linked by intermolecular O—H⋯O hydrogen bonds into a supramolecular three-dimensional twofold interpenetrating hydrogen-bonded network.

In the title compound, C 19 H 16 O 4 , there are two 4-hydroxybenzyl substituents on the oxan-4-one (tetrahydropyran-4one) ring, which exhibits an envelope conformation. The dihedral angles between pyranone ring and the two benzene rings are 26.69 (9) and 36.01 (9) while the benzene rings make a dihedral angle of 20.88 (10) . In the crystal, molecules are linked by intermolecular O-HÁ Á ÁO hydrogen bonds into a supramolecular three-dimensional twofold interpenetrating hydrogen-bonded network.
We thank the projects of China National Natural Science Funds, Guangdong Provincial Science Foundation and the 211 project of Guangdong Province for support.

Comment
For thousands of years Eastern medicine has used curcumin, the major component of turmeric, for a wide range of health benefits, but only in recent times has its biological action been understood. Curcumin possesses a wide spectrum of pharmacological activities including anti-oxidant, anti-inflammatory, antiviral, antifungal, cancer chemo preventive, cancer chemotherapeutic properties (Maheshwari et al., 2006). As the limitation of solubility, stability and activity of curcumin for clinical application, many series of curcumin analoges with a monoketone function have attracted interests in trial of improving the properties (Liang et al., 2009). This class of compounds is readily synthesized by reacting a substituted benzaldehyde with tetrahydropyran-4-one; in the case of the title compound 4-hydroxybenzaldehyde was used as the reactant.
The compound was purified by re-crystallization from THF and characterized by NMR spectrum and ESI mass spectrum.
The analytical and spectroscopic data are consistent with the proposed structure given in Scheme 1. The molecular structure of the title compound contains the two 4-methylbenzyl substituents on the tetrahydropyran-4-one and the six-member ring adopts an envelope conformation with the flap oxygen atom displaced by 0.648 (8) Å from the plane of the other five atoms ( Figure 1). Similar structures have been observed in the literature (Abaee et al., 2008;Du et al.,2006).
The dihedral angles formed between the mean plane through the six atoms of the pyranone ring and two benzene rings of 4-methylbenzyl groups are 26.69 (9) and 36.01 (9)°, the corresponding dihedral angles between two benzene rings of 4-methylbenzyl groups is 20.88 (10) °.
In the crystal packing, intermolecular O-H···O hydrogen bonds ( Figure 2, table 1) connect the molecules into a supramolecular three-dimensional two-fold interpenetrating hydrogen bonding network ( Figure 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.
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 > 2sigma(F 2 ) is used only for calculating R-factors(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.