Sulfuric Acid → 4-Bromo-5-formyl-benzo[1,3]dioxole-2-carboxylic acid methyl ester

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Reaction Steps

To a mixture of 2-bromo-3,4-dihydroxy-benzaldehyde (2.17 g, 10.0 mmol) and K2CO3 (5.56 g, 40.2 mmol) in n-propanol (25 mL) was added dibromoacetic acid (2.18, 10.0 mmol) and the mixture was heated at reflux temperature for 24 h. After cooling to room temperature, another portion of dibromoacetic acid (1.75 g, 8.0 mmol) was added. The mixture was stirred at reflux for 46 h. n-Propanol was evaporated and water (30 mL) was added. The resulting aqueous solution was acidified to pH 2 by adding 1 N HCl and extracted with ethyl acetate (3×100 mL). The combined organic layers were dried (MgSO4) and evaporated in vacuo to afford crude 4-bromo-5-formyl-benzo[1,3]dioxole-2-carboxylic acid (1.34 g) as a brownish solid. This crude product was dissolved in anhydrous methanol (50 mL) and conc. H2SO4 (5 mL) was added drop by drop. The resulting mixture was refluxed overnight and cooled to room temperature. Water (50 mL) was added and the resulting aqueous solution was extracted with ethyl acetate (100 mL×3). The combined organic layers were dried (MgSO4) and evaporated in vacuo. The residue was purified by flash column chromatography (ethyl acetate:hexane=5:95) to furnish 4-bromo-5-formyl-benzo[1,3]dioxole-2-carboxylic acid methyl ester as a white solid.

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