General procedure: triethylamine (NEt3, 56.6 g, 0.56 mol) was slowly added dropwise to stirred formic acid (64.4 g, 1.4 mol) at 58 °C. Subsequently, N,N-dimethylformamide (DMF, 150 ml), cyclic (sub)isopropyl malonate (Meldrum acid, 57.6 g, 0.4 mol) and m-nitrobenzaldehyde (2a-c, 60.4 g, 0.4 mol) were added to the reaction system. The reaction mixture was heated to reflux and maintained for 4 hours. After completion of the reaction, the solvent was removed by vacuum evaporation. The residue was ground with distilled water (1000 ml) and acidified with concentrated hydrochloric acid. After acidification, the product generated by hydrochloric acid precipitation was collected by filtration, dried in air and finally recrystallized by ethyl acetate (3a) or carbon tetrachloride (3b, c) to give the pure 3-(3-nitrophenyl)propionic acid.
