6,8-Diiodo-5,7-dimethoxy-4-methylcoumarin

In the title compound, C12H10I2O4, the methoxy groups are twisted considerably with respect to the plane of the aromatic ring [CH3—O—C—C torsion angles = −85.9 (3) and −92.8 (3)°]. In the crystal, molecules are linked by weak C—H⋯O hydrogen bonds and O⋯I contacts [3.194 (2) Å].


Comment
Coumarin is the simplest member of the group of oxygen heterocyclics called benzo-2-pyrone. Coumarins are an important class of compounds due to their presence in natural products as well as their medicinal applications such as anti-inflammatory (Lin et al., 2006), anti-viral (Massimo et al., 2003), antioxidant (Tyagi et al., 2003), antibacterial (Nawrot-Modranka et al., 2006), antifungal (Sardari et al., 1999), anti-HIV (Huang et al., 2005) and as anti-carcinogenic (Elinos-Baez et al., 2005). Besides the wide spectrum of biological applications of coumarin and its derivatives, the chemical literature also embodies their applications as cosmetics, optical brightening agents, and laser dyes. A recent report has revealed the anion sensing ability of some coumarin derivatives. Among various coumarin derivatives, recent pharmacological evaluation of iodocoumarins as cannabinoid receptor antagonists and inverse agonists has been done. Iodocoumarins such as 8-iodo-7hydroxycoumarin exhibited moderate activity and 8-iodo-5,7-dihydroxycoumarin displayed good antimicrobial properties with MIC values <100 µg/ml. Also, iodocoumarins had been successfully used for the optimization of reaction conditions and kinetic studies in high throughput format. Because of the biological and pharmaceutical importance of iodocoumarins, several protocols for the synthesis have been reported.
In the light of the mentioned above we planned to synthesize iodocoumarins by reaction of 5,7-dimethoxy-4-methylcoumarin with iodine in basic media (Ali & Ilyas, 1986).
In the molecule of the title compound ( Fig. 1), the best plane through the aromatic ring shows an r.m.s. deviation of 0.0154 Å; the O1-C2-C3-C4-C10-C9 ring shows a slightly larger deviation from planarity, with an r.m.s. deviation of 0.0189 Å. The angle between these two planes is 4.96 (11)°.
The methoxy groups are considerably twisted with respect to the plane of the aromatic ring as indicated by the torsion angles C12-O3-C5-C6 [-85.9 (3)°] and C13-O4-C7-C6 [90.7 (3)°]. The iodine atoms are almost in the plane of the benzene ring and the methyl group is slightly out of the pyrone ring plane.
The molecules are linked across an inversion centre by one weak hydrogen bond of the C-H···O type (Fig. 2, Table 2).

Experimental
To a stirred solution of 5,7-dimethoxy-4-methylcoumarin (2.20 g, 10 mmol) in 15-20 ml of methanol containing 8.2 g KOH was dropwise added to a solution of I 2 (2.56 g, 10 mmol) over a period of 30 min and stirred at room temperature for about 2 hours. The reaction mixture was poured into water and residual iodine was removed by washing with sodium thiosulphate.
On treatment with sodium thiosulphate we obtained a precipitate which was filtered and crystallized with CHCl 3 -MeOH as white crystals (300 mg, m.p. 490 K).
supplementary materials sup-2 Refinement All H atoms were located in a difference Fourier synthesis, placed in calculated positions and refined as riding on their parent atoms, using SHELXL97 (Sheldrick, 2008) defaults. Fig. 1. A plot of the title compound. Displacement ellipsoids are drawn at the 50% probability level.

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. 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.