Methyl 3,3,6,6-tetramethyl-1,8-dioxo-4,5,7,9-tetrahydro-2H-xanthene-9-carboxylate

The title molecule is built by annulation of a half-chair cyclohexenone and a twist-cyclohexenone to a flat 4-H-pyrane boat. In the crystal, molecules are connected via van der Waals interactions and C—H⋯O hydrogen bonds.

The title molecule, C 19 H 24 O 5 , is built by annulation of a half-chair cyclohexenone and a twist-cyclohexenone to a flat 4-H-pyrane boat. In the crystal, molecules are connected via van der Waals interactions and C-HÁ Á ÁO hydrogen bonds.
The molecule is composed of two dimethylcyclohexenone units annulated to a central 4H-pyrane (Fig. 1). While the conformation of the latter is a flat boat, one cyclohexenone (C2-C7) forms a half-chair and the other (C9-C14) has a twist form. The pyrane boat promotes a folded shape of the molecule, the angle between the mean planes through atoms C1-C3/C6/C7/O8 and O8/C9/C10/C13//C14 being 22.42 (11) , with maximum deviations from the mean planes at O8 [À0.1046 (18)  Four molecules occupy the monoclinic unit cell, the packing in the cell being dominated by van der Waals interactions and hydrogen-bonding interactions (Table 1 and Fig. 2). The C-HÁ Á ÁO hydrogen bonds (Steiner, 1996) C18-H18AÁ Á ÁO17 and C18-H18AÁ Á ÁO19 form a hydrogen-bonded dimer while the C6-H6BÁ Á ÁO24 interaction connects two molecules related by the c-glide plane. data reports Synthesis and crystallization Dimedone (7.01 g, 0.05 mol, 1 eq.) and triethylamine (5.05 g, 50 mmol, 6.9 ml, 1 eq.) were dissolved in dichloromethane (25 ml) in a 250 ml flask under nitrogen. Methyl chloromethoxyacetate (5.9 ml, 6.49 g, 0.525 mol, 1.05 eq.) was added dropwise to the ice-cooled mixture under stirring and the stirring was continued for 75 min at room temperature and a further 3 h under reflux conditions. The solvent was evaporated, methyl tert-butyl ether was added to the suspension and triethyl ammonium chloride was removed via filtration. The etheral layer was washed with aqueous sodium carbonate and brine, and dried over sodium sulfate. Evaporation of the solvent and chromatography (silica gel, petroleum ether/ethyl acetate = 3/1, R f = 3:1) yielded 0.83 g (2.5 mmol, 5%) of the title compound as colourless crystals with m.p. = 474-478 K. The main product yield was 83%. Crystals of the title compound were obtained from a solution in ethyl acetate. IR: 2959IR: , 2875IR: , 1728IR: , 1663IR: , 1368IR: , 1193

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2.

Figure 1
Perspective view of the title compound. Displacement ellipsoids are drawn at the 50% probability level.

data-1
IUCrData ( where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.002 Δρ max = 0.24 e Å −3 Δρ min = −0.30 e Å −3 Special details 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. Hydrogen atoms attached to carbons were placed at calculated positions and were refined in the ridingmodel approximation with C-H = 0.95 Å, and with U iso (H) = 1.2 U eq (C).