GENERAL METHOD: 3,4-difluorobenzaldehyde (10 mmol), malonic acid (30 mmol, 3.12 g) and piperidine (0.5 mL) were dissolved in pyridine (20 mL) and the reaction mixture was heated to reflux for 4 hours. Upon completion of the reaction, the solution was cooled to room temperature and slowly poured into pre-cooled aqueous 3 M HCl solution (100 mL). The precipitated white solid was collected by filtration and washed sequentially with deionized water (350 mL), 5% w/v aqueous NaHCO3 solution (20 mL) and deionized water (250 mL). The resulting solid was dried in an oven at 60 °C. If necessary, the crude product can be purified by recrystallization using a solvent mixture of EtOH/H2O.4.3.1. (E)-3-(3,4-difluorophenyl)acrylic acid (2j). Yield: 1.70 g (92%).1H NMR (DMSO-d6, 400 MHz) δ: 7.85-7.91 (m, 1H), 7.55-7.57 (m, 1H), 7.56 (d, J=16.0 Hz, 1H), 7.43-7.50 (m, 1H), 6.57 (d, J=16.0 Hz, 1H).13C NMR (DMSO-d6, 101 MHz) δ: 167.30, 150.35 (dd, 1JCF=248 Hz, 2JCF=13 Hz), 149.64 (dd, 1JCF=244 Hz, 2JCF=13 Hz), 141.64, 132.03 (dd, 3JCF=6 Hz, 4JCF=4 Hz). 125.82 (dd, 3JCF=7 Hz, 4JCF=3 Hz), 120.68, 117.88 (d, 2JCF=17 Hz), 116.65 (d, 2JCF=18 Hz).
