Crystal structure of (E)-3-(2-hydroxy-4-methylphenyl)-1-(2,4,6-trimethoxyphenyl)prop-2-en-1-one

The title compound consists of a 2-hydroxy-4-methylphenyl ring, a 2,4,6-trimethoxyphenyl ring and a prop-2-en-1-one connecting bridge. The overall conformations of the title compound are discussed and compared with those of related structures. In the crystal, molecules are consolidated by O—H⋯O hydrogen bonds and weak C—H⋯O interactions.


Chemical context
Chalcones (1,3-diarylprop-2-en-1-ones) are precursors of flavonoids and isoflavonoids in the plant kingdom (Ni et al., 2004;Sahu et al., 2012). Structurally, they consist of two aryl groups linked by an , -unsaturated ketone system (Ibrahim et al., 2012;Kumar et al., 2013), whereby the aryl groups can carry a variety of substituents such as hydroxyl, methoxy and alkenyl groups, which are by far the most commonly encountered ones in nature. With their structural simplicity and the associated ease of synthesis, chalcone compounds have attracted a considerable amount of attention because of their important pharmacological properties such as antioxidative (Aoki et al., 2008), anti-inflammatory (Israf et al., 2007), anti-gout (Jang et al., 2014), anti-histaminic (Yamamoto et al., 2004), anti-obesity (Birari et al., 2011), anti-protozoal (Chen et al., 1993), hypnotic (Cho et al., 2011) and anti-spasmodic (Sato et al., 2007) effects. In a continuation of our ongoing research on the properties of various chalcone derivatives (Sim et al., 2017, Kwong et al., 2018, we report herein the synthesis and crystal structure determination of the title compound, C 19 H 20 O 5 , (I).

Supramolecular features
In the crystal, the molecules are linked into chains parallel to the b axis via classical O1-H1BÁ Á ÁO2 i hydrogen bonds (Fig. 3a). These chains are further connected into inversionrelated dimeric chains by weak C17-H17AÁ Á ÁO1 ii intermolecular interactions (Fig. 3b, Table 1). General chemical diagram showing torsion angles, 1 , 2 and 3 .

Figure 1
The title molecule with the atom-labelling scheme and displacement ellipsoids drawn at the 50% ellipsoid probability level.  Grealis et al., 2013). As in (I), the molecules of all these structures adopt a trans configuration with respect to C C double bond (C6-C7-C8-C9 torsion angles = 175.5-179.1 ). Although, 1 for all of the structures indicates an antiperiplanar conformation (Table 2), in BUFMOF it deviates slightly from planarity ( 1 = 152.7 ) whereas 1 for the other molecules is approximately 180 ( 1 = 174.1-176.0 , Table 2).
Regarding the enone bridge, the torsion angle 2 indicates that all of the structures are relatively planar ( 2 = À4.8-7.6 ). The torsion angles 3 always almost indicate a perpendicular arrangement ( 3 = 67.6-88.6 ). This might arise from the steric repulsion between the carbonyl group and the attached 2,4,6trimethoxyphenyl ring. This results in an overall L-shape for all of the structures, with the dihedral angle between the mean planes of the two aromatic rings being 61.6-80.4 .

Synthesis and crystallization
A reaction scheme for the synthesis of the title compound is given in Fig. 4. A solution of trimethoxyacetophenone (2 mmol) in 20 mL MeOH, LiOH (2.4 mmol) and 2-hydroxy-4-methylbenzaldehyde (1.6 mmol) was stirred at 368 K and the reaction progress was monitored by TLC. The reaction was quenched with diluted hydrochloric acid to pH = 6 and extracted with ethyl acetate. The organic layer was washed with aqueous NaHCO 3 , water, and brine, successively. The organic layer was dried over anhydrous Na 2 SO 4 and then concentrated to provide the product as a brown powder. The residue was purified by column chromatography with petroleum ether/ethyl acetate (10:1) as an eluent to afford the target compound (Yan et al., 2016). Slow evaporation from an acetonitrile-water mixture provided X-ray quality crystals for the target chalcone compound.  : 194.3, 162.2, 158.4, 157.1, 142.5, 140.2, 128.8, 127.9, 121.1, 118.9, 117.0, 111.9, 91.6, 56.2, 55.9, 21.6. CHN Elemental analysis: Calculated for C 19 H 20 O 5 : C, 69.50; H, 6.14; N. Found: C, 67.81; H, 5.72; N, 0.00.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3 Reaction scheme for the synthesis of the title chalcone.
The dihedral angle is that between the mean planes of the aromatic rings.

Computing details
Data collection: APEX2 (Bruker, 2012); cell refinement: SAINT (Bruker, 2012); data reduction: SAINT (Bruker, 2012); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2013 (Sheldrick, 2015); molecular graphics: SHELXL2013 (Sheldrick, 2015) and Mercury (Macrae et al., 2006); software used to prepare material for publication: SHELXL2013 (Sheldrick, 2015) and PLATON (Spek, 2009).  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.