A 50 mL Schlenk tube was charged with (3-fluorophenyl)boronic acid (140 mg, 1.0 mmol), 5-bromo-2-fluorobenzoic acid (263 mg, 1.2 mmol), tetrakis(triphenylphosphine)palladium (0) (58 mg, 0.05 mmol) and cesium carbonate (1.3 g, 4.0 mmol). Ethanol (5 mL) and toluene (5 mL) were added and the tube was sealed and heated at 80° C. for 3 h. The cooled mixture was transferred to a flask, washing with ethanol, and concentrated in vacuo. The residue was diluted with water (10 mL) and extracted with EtOAc (2×10 mL). The aqueous phase was acidified with 1.0 N aqueous HCl (10 mL) and extracted with EtOAc (3×10 mL). The extracts were dried (Na2SO4), filtered and concentrated in vacuo. 1H-NMR showed the desired product, 3′,4-difluoro-[1,1′-biphenyl]-3-carboxylic acid, was slightly contaminated with 2-fluorobenzoic acid. The impure product (215 mg, ˜92%) was used without further purification.
