Crystal structure of 2-(3,4-dimethoxyphenyl)-3-hydroxy-4H-chromen-4-one

In the title compound, C17H14O5, the dimethoxy-substituted benzene ring is twisted relative to the 4H-chromenon skeleton (r.m.s. deviation = 0.015 Å) by 5.2 (4)°. The C atoms of the methoxy groups lie close to the plane of their attached benzene ring [deviations = 0.036 (3) and 0.290 (3)Å for the meta and para substituents, respectively]. An intramolecular O—H⋯O hydrogen bond closes an S(5) ring. In the cystal, inversion dimers linked by pairs of O—H⋯O hydrogen bonds generate R 2 2(10) loops and C—H⋯O interactions connect the dimers into [010] chains.


S2.1. Synthesis and crystallization
Chalcone (1 mmol, 284 mg) was suspended in 15 ml of MeOH / THF (2:1), and 0.5 mL NaOH (30% aq.) was added to produce a red solution, which was cooled to 0°C. To this reaction mixture, was added 1 ml H 2 O 2 (32% aq.) and the solution was stirred for 2h at room temperature. The resulting solution was poured into water (100 ml) and was acidified with 3M HCl. The pale yellow precipitate obtained was filtered and washed with ethanol give the titled compound (57%).
Recrystallization in the ethanol solvent gave orange blocks of the title compound (mp: 475-476K)

S3. Results and discussion
Flavonoids are one of secondary metabolites in plants with C6-C3-C6 skeleton, which include flavones, flavonols, chalcones and isoflavones. Variety of flanonols have been isolated from natural sources and syntheized (Bendaikha et al. 2014;Prescott et al. 2013), because they have shown wide spectrum of biological activities (Lee et al. 2014;Dias et al. 2013). Inspired by the important biological activities of flavonols, our research project has been focused on development of novel flavonols which show broad range of biological activities. Because it has been well established that the presence and position of hydroxy and methoxy substituents plays an important role in determining the biological activity of flavonoids (Singh et al. 2014), the title compound was synthesized and its crystal structure was determined. A starting material, chalcone, (E)-3-(3,4-dimethoxyphenyl)-1-(2-hydroxyphenyl)prop-2-en-1-one, was prepared by the previously reported methods (Yong et al. 2013). Flavonol was obtained by oxidative cyclization of the chalcone with H 2 O 2 in alkaline methanol medium (Lee et al. 2014).
In the title compound, C 17 H 14 O 5 , dimethoxy substituted benzene ring is twisted relative to 4H-chromenon skeleton by 5.2 (4) o . The methoxy groups at C12 and C13 are tilted from benzene ring by 2.7 (3) o and 8.9 (4) o , respectively. In the crystal, pairs of O-H-O hydrogen bonds form inversion dimer with graph-set notation R 2 2 (10) (Marciniec et al. 2013).
In addition, each molecule contains intramolecular O-H-O hydrogen bond with a S(5) motif. Examples of structures of flavonols have been published (Serdiuk et al., 2013;Yu et al., 2006).  Part of the crystal structure with intermolecular O-H···O hydrogen bonds shown as dashed lines where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.41 e Å −3 Δρ min = −0.56 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.

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