A Knoevenagel condensation reaction catalyzed by piperidine (0.5 mL, 4.9 mmol) in pyridine (11.4 mL) was carried out with 5-bromo-2-fluorobenzaldehyde (5.0 g, 24.6 mmol) and malonic acid (5.6 g, 53.7 mmol). The reaction mixture was stirred at 100 °C for 3 h. After completion of the reaction, the solvent was removed by concentration under reduced pressure. Distilled water was added to the concentrated mixture and the precipitate was collected by filtration. The resulting crude product was purified by recrystallization with ethanol to give the final 5-bromo-2-fluorocinnamic acid (1.3 g, white solid). The structure of the product was confirmed by 1H NMR (400 MHz, CD3OD): δ 7.89 (d, 1H), 7.74-7.70 (m, 2H), 7.15 (t, 1H), 6.62 (d, 1H).
