9-(2,4-Difluorophenyl)-3,3,6,6-tetramethyl-3,4,5,6,7,9-hexahydro-2H-xanthene-1,8-dione

In the title compound, C23H24F2O3, the central pyran ring has a flat-boat conformation, whereas the two fused cyclohexenone rings adopt envelope conformations, with the C atom bearing the dimethyl substituent being the flap atom in each case. The pyran ring mean plane and the difluorophenyl ring are almost normal to each other, making a dihedral angle of 87.55 (4)°. In the crystal, molecules are linked by pairs of C—H⋯O hydrogen bonds, forming inversion dimers with an R 2 2(8) ring motif. The F atom at position 2 on the difluorophenyl ring is disordered over the 2- and 6-positions, and has a refined occupancy ratio of 0.932 (3):0.068 (3).

In the title compound, C 23 H 24 F 2 O 3 , the central pyran ring has a flat-boat conformation, whereas the two fused cyclohexenone rings adopt envelope conformations, with the C atom bearing the dimethyl substituent being the flap atom in each case. The pyran ring mean plane and the difluorophenyl ring are almost normal to each other, making a dihedral angle of 87.55 (4) . In the crystal, molecules are linked by pairs of C-HÁ Á ÁO hydrogen bonds, forming inversion dimers with an R 2 2 (8) ring motif. The F atom at position 2 on the difluorophenyl ring is disordered over the 2-and 6-positions, and has a refined occupancy ratio of 0.932 (3):0.068 (3).

Comment
Xanthene is the parent compound of a number of naturally occurring substances and some synthetic dyes. Xanthene derivatives are used as dyes (Hilderbrand & Weissleder, 2007) and are used in medicine as they possess biological properties like antibacterial, antiviral and anti-inflammatory activities (Jonathan et al., 1988). Ehretianone, a quinonoid xanthene was reported to possess anti-snake venom activity (Selvanayagam et al., 1996;Lambert et al., 1997;Poupelin et al., 1978;Hideo, 1981). In view of the importance of the Xanthene derivatives we have synthesized the title compound and report herein on its crystal structure.
In the title molecule, Fig. 1 In the crystal, molecules are linked by a pair of C-H···O hydrogen bonds ( Fig. 2 and Table 1) forming inversion dimers with an R 2 2 (8) ring motif (Bernstein et al., 1995).

Refinement
Atom F1 on the difluorophenyl ring is slightly disordered, being attached to atoms C23 and C19 with a refined occupancy ratio of 0.932 (3) respectively, with U iso (H) = 1.5U eq (C-methyl) and = 1.2U eq (C) for other H atoms.

Figure 1
The molecular structure of the title compound, with atom labelling. Displacement ellipsoids are drawn at the 50% probability level. The crystal packing of the title compound viewed along the a axis. The C-H···O hydrogen bonds are shown as dashed lines -see Table 1 for details.

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