3-Hydroxy-2-[(2-hydroxy-4,4-dimethyl-6-oxocyclohex-1-en-1-yl)(3-nitrophenyl)methyl]-5,5-dimethylcyclohex-2-en-1-one

Each of the cyclohexenone rings in the title compound, C23H27NO6, adopts a half-chair (envelope) conformation with the C atom carrying the methyl groups lying out of the plane defined by the five remaining C atoms; the O atoms lie to the same side of the molecule as the respective >C(CH3)2 atoms. The hydroxy and carbonyl O atoms face each other and are orientated to allow for the formation of two intramolecular O—H⋯O hydrogen bonds. In the crystal, the presence of C—H⋯O contacts leads to the formation of supramolecular chains along the b axis. These aggregate into layers that stack along c.

Each of the cyclohexenone rings in the title compound, C 23 H 27 NO 6 , adopts a half-chair (envelope) conformation with the C atom carrying the methyl groups lying out of the plane defined by the five remaining C atoms; the O atoms lie to the same side of the molecule as the respective >C(CH 3 ) 2 atoms. The hydroxy and carbonyl O atoms face each other and are orientated to allow for the formation of two intramolecular O-HÁ Á ÁO hydrogen bonds. In the crystal, the presence of C-HÁ Á ÁO contacts leads to the formation of supramolecular chains along the b axis. These aggregate into layers that stack along c.   Table 1 Hydrogen-bond geometry (Å , ). (ii) Àx þ 2; Ày þ 1; Àz þ 1; (iii) Àx þ 2; Ày þ 2; Àz þ 1.

Comment
Xanthenes are known for to possess various biological properties including anti-bacterial, anti-viral and anti-inflammatory activities (Jonathan et al., 1988). In particular, xanthenedione derivatives constitute a structural unit in several natural products (Hatakeyama et al., 1988), and they are valuable synthons because of the inherent reactivity of the in-built pyran ring (Shchekotikhin & Nikolaeva, 2006). Xanthene derivatives are also very useful and important organic compounds widely used as dyes (Hilderbrand & Weissleder, 2007), in laser technologies, and as fluorescent materials for visualization of biomolecules (Pohlers & Scaiano, 1997).
The molecular structure of the title compound, Fig. 1, features two cyclohexene rings, each with a half-chair conformation as, in each case, the C4 and C13 atoms, i.e. carrying two methyl groups, lie above the respective least-squares plane through the remaining five carbon atoms. For each ring, the O atoms lie to the same side of the molecule as the C4 or C13 atoms.
The hydroxyl-and carbonyl-O atoms of one cyclohexene ring face the carbonyl-and hydroxyl-O atoms of the other to allow for the formation of intramolecular O-H···O hydrogen bonds, Table 1. The nitro group is co-planar with the benzene ring to which it is attached as seen in the O5-N1-C22-C21 torsion angle of -176.02 (11) °. The nitro-substituted benzene ring occupies a position almost side-on to both cyclohexene rings.
The most prominent intermolecular interactions in the crystal packing are of the type C-H···O, Table 1. These serve to link molecules into a supramolecular chain along the b axis, Fig. 2. The chains pack into layers in the ab plane which stack along the c axis, Fig. 3.

Experimental
A mixture of 3-nitrobenaldehyde (0.377 g, 0.0025 mol), dimedone (0.7 g, 0.005 mol) was refluxed in acetonitrile (20 ml) for 3 h. The progress of the reaction was monitored by TLC. After completion of the reaction, the solution was left for 2 days to precipitate the solid product. The product was recrystallized by slow evaporation of its acetonitrile solution which yielded colourless blocks of (I). Yield: 72%. M.pt. 443-445 K.