Methyl 3,5-dibromo-4-methylbenzoate

In the title compound, C9H8Br2O2, the molecule is essentially planar with an r.m.s. deviation of 0.0652 Å from the mean plane through all non-H atoms and a dihedral angle of 7.1 (2)° between the benzene ring plane and the carboxylate substituent. In the crystal structure, weak C—H⋯Br hydrogen bonds and weak intermolecular O⋯Br contacts [3.095 (2) Å], link adjacent molecules into layers parallel to (102). Additional weak intermolecular C—H⋯O hydrogen bond interactions stack the layers above and below the molecular plane and down the a axis.

In the title compound, C 9 H 8 Br 2 O 2 , the molecule is essentially planar with an r.m.s. deviation of 0.0652 Å from the mean plane through all non-H atoms and a dihedral angle of 7.1 (2) between the benzene ring plane and the carboxylate substituent. In the crystal structure, weak C-HÁ Á ÁBr hydrogen bonds and weak intermolecular OÁ Á ÁBr contacts [3.095 (2) Å ], link adjacent molecules into layers parallel to (102). Additional weak intermolecular C-HÁ Á ÁO hydrogen bond interactions stack the layers above and below the molecular plane and down the a axis.

Comment
The title ester, (I), Fig. 1, is an important intermediate towards synthesis of 3,5-dimethoxyphenylacetic acid, a key intermediate in the synthesis of a variety of natural products. These include the sclerotiorin group of fungal metabolites (Gray & Whalley, 1971), isochromans related to sclerotiorin pigments (Saeed & Rama, 1994) and isocoumarins like 7-methylmellein (Harris & Mantle, 2001) and stellatin (Simpson, 1978). C 9 H 8 O 2 Br 2 , (I), was prepared by bromination of methyl 4-methylbenzoate in presence of anhydrous aluminum chloride using an excess of calalyst and no solvent.
The molecule is essentially flat with an rms deviation of 0.0652 Å from the mean plane through all non-hydrogen atoms.

Experimental
Anhydrous aluminum chloride (1.60 mmol) was added portionwise to stirred methyl 4-methylbenzoate (0.6 mmol) at 0°C under a nitrogen atmosphere. Bromine was added over 45 min. and the mixture was further stirred for 30 min at room temperature and at 80 °C for 1 h. The mixture was cooled to room temperature, treated with cold methanol (100 ml) and then stirred overnight. The crude product was filtered and washed with methanol at 30°C then recrystallized from methanol at 10°C to to afford the title compound (86%) as colourless crystals: Anal. calcd. for C 9 H 8 Br 2 O 2 : C, 35.10; H, 2.62; found: C, 35.23; H, 2.67 % Refinement H-atoms were positioned geometrically and refined using a riding model with d(C-H) = 0.95 Å, U iso = 1.2U eq (C) for aromatic and d(C-H) = 0.98 Å, U iso = 1.5U eq (C) for methyl C atoms.
supplementary materials sup-2 Figures   Fig. 1. The structure of (I) with displacement ellipsoids for the non-hydrogen atoms 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.