4-Hydroxy-3-[(4-hydroxy-6,7-dimethyl-2-oxo-2H-chromen-3-yl)(4-oxo-4H-chromen-3-yl)methyl]-6,7-dimethyl-2H-chromen-2-one

In the title compound, C32H24O8, the molecular structure is disordered over two positions with refined site occupancies of 0.8746 (10) and 0.1254 (10). The mean plane of the three chromeno rings make dihedral angles with each other of 65.12 (4), 62.91 (4) and 59.70 (4)° in the major occupancy component and 59.1 (3), 66.1 (3) and 58.8 (3)° in the minor component. Intramolecular O—H⋯O hydrogen bonds stabilize the molecular structure and the crystal structure is stabilized by weak C–H⋯π and π–π interactions [centroid–centroid distances 3.496 (6)–3.672 (7) Å].


Comment
The oxygen-containing chromone heterocycles are ubiquitous in plants (Waring, 1979). They form basic nucleus of flavones (Dewick, 1994) and have been found in many biologically active molecules with a broad range of applications in the pharmaceutical industry (Rich, 1990). These derivatives are an important class of compounds, possessing a large number of pharmacological activities such as anti-HIV (Masami et al., 2007), potentially anti-inflammatory (Khan et al., 2010), antibacterial (Nawrot-Modranka et al., 2006), antiallergic (Ellis et al., 1978 and anticancer (Raj et al., 2010) activities.

Experimental
A mixture of 6,7-dimethyl-4-hydroxycoumarin (1.05 mmol, 200 mg) and 3-formyl chromone (0.52 mmol, 91 mg) was prepared in ethanol (10 ml) and acetic acid (0.5 ml) was added to it. The reaction mixture was refluxed on water bath for 6 h. The completion of the reaction was monitored by TLC. After completion of the reaction, the crystalline solid was filtered, washed with ethanol and purified by recrystallization from chloroform-methanol mixture to give the pure title compound in 75% yield.

Refinement
The molecular structure is disordered over two positions with refined site occupancies of 0.8746 (10) and 0.1254 (10).
The minor component was refined isotropically. The same U ij parameters were used for the atoms C5A/C31A/C32A. All disordered atoms were subjected to rigid bond and similarity restraints. One of the chromeno ring was restrained to be planar.   4-Hydroxy-3-[(4-hydroxy-6,7-dimethyl-2-oxo-2H-chromen-3-yl)(4-oxo-4H-chromen-3-yl)methyl]-6,7-dimethyl-2H-chromen-2-one  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 Rfactors(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 )
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