4a-Hy-droxy-9-(2-meth-oxy-phen-yl)-4,4a,5,6,7,8,9,9a-octa-hydro-3H-xanthene-1,8(2H)-dione.

In the title compound, C(20)H(22)O(5), an S(6) ring motif is formed by an intra-molecular C-H⋯O hydrogen bond, which contributes to the stabilization of the mol-ecule. In the xanthene system, the cyclo-hexane ring adopts a chair conformation, the cyclo-hexene ring adopts a half-boat conformation and the tetra-hydro-pyran ring adopts a half-chair conformation. The mean plane of the four essentially planar atoms of the tetra-hydro-pyran ring [r.m.s deviation = 0.092 (1) Å] forms a dihedral angle of 64.13 (6)° with the mean plane of the meth-oxy-phenyl group. In the crystal, inter-molecular O-H⋯O and weak C-H⋯O hydrogen bonds link mol-ecules into chains along the a axis, which are further stabilized by C-H⋯π inter-actions.


Comment
Xanthene derivatives are very important heterocyclic compounds and due to their useful spectroscopic properties, they have been widely used as dyes, fluorescent materials for visualization of bio-molecules and in laser technologies (Menchen et al., 2003;Saint-Ruf et al., 1972;Ion et al., 1998). They have been reported for their agricultural bactericide activity, photodynamic therapy, antiflammatory effect and antiviral activity (Knight & Stephens, 1989;Jonathan et al., 1988). Due to their wide range of applications, these compounds have received a great deal of attention in connection with their synthesis.
In the synthesis of these compounds, intermediates play a key role, because these compounds can be easily converted into acridines and other biological active compounds.

Experimental
A mixture of 2-methoxybenzaldehyde (0.365 ml, 0.0025 mol) and 1,3-cyclohexanedione (0.56 g, 0.005 mol) was refluxed in acetonitrile for 3 h. The progress of the reaction was monitored by TLC. After completion of the reaction, it was kept for 2 days for solid formation. The pure product was obtained by recrystallization of the crude product from ethanol. M.p.: 493-495 K, yield: 72%.

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