Crystal structure of (E)-4,6-dimethoxy-2-(4-methoxystyryl)-3-methylbenzaldehyde

In the title molecule, C19H20O4, the central C=C double bond adopts an E configuration. The dihedral angle formed by the planes of the two benzene rings is 83.57 (12)°. The three methoxy groups are essentially coplanar with the benzene rings to which they are attached, with C C—O—C torsion angles of −0.2 (3), −2.3 (3) and −4.1 (3)°.

Supporting information for this paper is available from the IUCr electronic archives (Reference: LH5786).

S1. Introduction
Resveratrol is part of a family of the stilbene polyphenols which has a general C6-C2-C6 carbon framework. Recent research has shown that resveratrol derivatives have diverse biological activities including anti-Alzheimer's disease (Li et al., 2014), anticancer (Chillemi et al., 2015), and anti-inflammatory (Chen et al., 2015). On our going research project of polyphenols (Shin et al., 2014), the title compound was synthesized and its crystal structure was determined.
After the methylation of hydroxyl groups in resveratrol, formylation of the resulting compound was performed (Fig 2).
The Vilslmeier formylation reaction gave two products depending on reaction conditions (Huang et al., 2007). The title compound (I) contains one formyl group and one methyl group at each ortho position of the dimethoxy-substituted benzene ring. Whereas compound (II) has only a formyl group at the ortho position of the benzene ring. The crystal structure of compound (II) has been published recently (Ge et al. 2013). In this report, the title compound (I) was synthesized and its crystal structure was determined. According to the literature (Ge et al. 2013), compound (II) contains two independent molecules in the asymmetric unit and the dihedral angle between the two benzene rings in each are 23.54 (12)°, and 31.11 (12)°. However, in (I), dihedral angle between the two benzene rings is 83.57 (12)° (Fig. 1). The

S2. Experimental
For an outline of the synthesis see Fig. 2. Resveratrol (A, 30 mmol, 6.8 g) was dissolved in 75 mL of aq. NaOH (10%) under ice-water bath conditions. To the above solution, was added DMS (50 mL) and the reaction mixture was stirred at room temperature for 24 h. After completion of this reaction, the mixture was extracted with EtOAc (50 mL x 3) and the combined organic layer was dried under MgSO 4 . Filtration and evaporation of the solvent gave a solid of compound B.
To a solution of compound B (10 mmol, 2.7 g) in 20 mL of DMF was added 2 mL of POCl 3 in an ice-water bath, and was stirred at room temperature for 4 h. The reaction mixture was poured into ice-water and stirred for 2 h. The reaction mixture was extracted with EtOAc (30 mL x 3). Evaporation of the organic solvent afforded mixture of products (I) and (II), which was purified by column chromatography. Recrystallization of solid (I) from ethanol gave single crystals which were suitable for X-ray diffraction (m.p.: 391-392 K).

S2.1. Refinement
H atoms bonded to C atoms were placed in calculated positions, with C-H distances in the range 0.95-0.98 Å, and included in the refinement in a riding-model approximation, with U iso (H) = 1.5U eq (C) for methyl H atoms and 1.5U eq (C) otherwise.

Figure 1
The molecular structure of the title compound, showing the atom labelling scheme and displacement ellipsoids drawn at the 30% probability level.

Figure 2
Synthetic scheme for preparation of resveratrol derivative compounds. where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.24 e Å −3 Δρ min = −0.31 e Å −3 Special details Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s 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 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.