9-(4-Hydroxy-3-methoxyphenyl)-3,3,6,6-tetramethyl-3,4,5,6-tetrahydro-9H-xanthene-1,8(2H,7H)-dione

In the title compound, C24H28O5, the two cyclohexene rings adopt envelope conformations, and the planes through the coplanar atoms makes dihedral angles of 82.86 (6) and 77.90 (6)° with the benzene ring. The two cyclohexene rings make a dihedral angle of 5.33 (6)° between their least-squares planes. The pyran ring adopts a flattened boat conformation. In the crystal packing, molecules are linked into two-dimensional networks parallel to the ab plane via O—H⋯O and C—H⋯O interactions.

In the title compound, C 24 H 28 O 5 , the two cyclohexene rings adopt envelope conformations, and the planes through the coplanar atoms makes dihedral angles of 82.86 (6) and 77.90 (6) with the benzene ring. The two cyclohexene rings make a dihedral angle of 5.33 (6) between their least-squares planes. The pyran ring adopts a flattened boat conformation. In the crystal packing, molecules are linked into twodimensional networks parallel to the ab plane via O-HÁ Á ÁO and C-HÁ Á ÁO interactions.

Comment
Xanthene derivatives especially benzoxanthenes are well-known in organic synthesis due to their biologically active properties such as anti-inflammatory (Hafez et al., 2008), antimicrobial (Ashry et al., 2006), antiviral (Sill & Sweet, 1977) activities and as well as being used in photodynamic therapy (Ion, 1997). Molecules based on the 9,9-dimethylxanthene moiety have inhibitory activity towards trypanothione reductase (TryR) (Chibale et al., 2003). In view of its importance in this field, the crystal structure of the title compound was determined and the results are presented here.

Experimental
The synthesis of the title compound was performed according to the procedure described in the literature (Venkatesan et al., 2008). A mixture of vanilin (90 mg, 0.59 mmol), dimedone (160 mg, 1.14 mmol), p-toluenesulfonic acid (2 mg) in MeOH (4 ml) and water (2 ml) was heated to 50 °C in N 2 atmosphere for about 20 min. Good quality crystals suitable for characterisation by X-ray crystallography were obtained by recrystallisation from hot methanol.

Special details
Experimental. The crystal was placed in the cold stream of an Oxford Cyrosystems Cobra open-flow nitrogen cryostat (Cosier & Glazer, 1986) operating at 100.0 (1) K.
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 > 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.