Methyl chloroacetate → 7-Bromo-5-fluorobenzofuran-2-carboxylic acid

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Methyl chloroacetate (7.6 mL, 86.8 mmol) was added to a mixture of 3-bromo-5-fluoro-2-hydroxy-benzaldehyde (9.5 g, 43.4 mmol), tetra-N-butyl-ammonium iodide (1.6 g, 4.34 mmol) and anhydrous potassium carbonate (24 g, 174 mmol). The reaction mixture was heated at 130° C. for 4 h, cooled to 0° C., diluted with tetrahydrofuran (100 mL) and then potassium hydroxide (17 g, 303 mmol) in water (100 mL). The mixture was stirred at rt for 18 h and then, concentrated under reduced pressure. The residue was acidified with HCl and extracted with ethyl acetate. The combined organic extracts were dried (Na2SO4), filtered and concentrated under reduced pressure. The crude compound was purified by flash chromatography (SiO2; toluene/EtOAc, 40/1) to give 7.0 g (63%) of the product.

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