(1E,4E)-1,5-Bis(2,6-difluorophenyl)penta-1,4-dien-3-one

The molecule of the title compound, C17H10F4O, is roughly planar, with a dihedral angle of 5.59 (14)° between the two phenyl rings. The molecule has an E conformation with respect to the olefinic bonds. In the crystal, molecules are connected through C—H⋯O hydrogen bonds and there is slipped π–π stacking [centroid–centroid distance = 3.7983 (18), slippage =1.309 ;Å] between symmetry-related benzene rings.


Comment
The title compound, (1E,4E)-1,5-bis (2,6-difluorophenyl) penta-1,4-dien-3-one (I), is one of mono-carbonyl analogues of curcumin designed and synthesized by our group.Curcumin (diferuloylmethane ) is the main component of turmeric, the powdered root of Curcuma longa Linn. Traditionally, curcumin has been used as a medicine for liver disease, indigestion, urinary tract diseases, rheumatoid arthritis, and insect bites (Aggarwal et al., 2007;Kamat et al., 2009). The pharmacological safety of curcumin has been demonstrated by its consumption for centuries at levels of up to 100 mg/day by people in certain countries (Pan et al., 1999). One potential problem with the clinical use of curcumin is its low bioavailability and poor absorption characteristics ( Sharma et al., 2007); however, curcumin remains an ideal leading compound for design of some effective analogues. In our previous study, a series of fluorine-containing, mono-carbonyl analogues of curcumin were designed and synthesized by the deletion of β-diketone moiety, and their bioactivities were evaluated Zhao et al., 2010a,b). Among those compounds, some analogues exhibited better anti-tumor properties and a wider anti-tumor spectrum than curcumin. As a continuation of our broad program of work on the synthesis and structural study of curcumin analogues, the title curcumin derivative has been obtained and an X-ray diffraction study was carried out.
Therefore, the structure of one of compounds (I), was further determined and analyzed using single-crystal X-ray diffraction.
Accumulation of detailed structural and pharmacological data facilitated the explanation of the observed structure-activity relationships and modeling of new compounds with potential biological activity.
The molecule (I), consists of two 2,6-difluoophenyl rings linked through a penta-1,4-dien-3-one chain (Fig. 1). The molecule displays an E conformation with respect to the olefinic bonds, exhibiting a butterfly-shaped geometry. The whole molecule is roughly planar with a dihedral angle between the two terminal phenyl rings of 5.59 (14)°. Among these derivatives, the structures of some of them were reported ( Liang et al., 2007;Zhao et al., 2009;Zhao et al., 2010a,b).
In the crystal, the molecule are connected through C-H···O hydrogen bonds and slippest π-π stacking between symmetry related phenyl rings (Tables 1 and 2 Experimental Acetone (7.5 mmol) was dissolved in ethanol (5 ml) and crushed KOH (15 mmol) was added. The flask was immersed in a bath of crushed ice and a solution of 2,6-difluorobenzaldehyde (15 mmol) in ethanol (5 mmol) was added. The reaction mixture was stirred at 300 K and completion of the reaction was monitored by thin-layer chromatography. Ice-cold water was added to the reaction mixture after 48 h and the yellow solid that separated was filtered off, washed with water and cold ethanol, dried and purified by column chromatography on silica gel (yield: 49.3%). Single crystals of the title compound were grown in a CH 2 Cl 2 /CH 3 OH mixture (5:2 v/v) by slow evaporation .

Refinement
The H atoms were positioned geometrically (C-H = 0.93 and 0.96 Å) and refined as riding with U iso (H) = 1.2U eq (C) or 1.5U eq (methyl C). Fig. 1. The molecular structure of the title compound with the atom labeling scheme. Displacement ellipsoids are drawn at the 30% probability level. Hydrogen atoms are represented as small spheres of arbitrary radii.

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.