General procedure: 2-fluorobenzaldehyde (20.0 mL, 189.9 mmol), 1-methylpiperazine (33.0 mL, 297.7 mmol) and potassium carbonate (40.0 g, 289.4 mmol) were dissolved in water (200 mL) and heated to reflux. After the reaction was completed, it was cooled to room temperature and the reaction mixture was extracted with ethyl acetate (2 x 150 mL). The organic phases were combined, washed with brine, dried over anhydrous magnesium sulfate, and concentrated under reduced pressure to afford the target product 2-(4-methylpiperazine)benzaldehyde (PP57, 38.6 g, 100%) as an orange oil. Its NMR hydrogen spectrum (CDCl3) data were as follows: δ 10.10 (s, 1H), 7.77 (dd, J = 7.9, 1.7 Hz, 1H), 7.51-7.48 (m, 1H), 7.10-7.06 (m, 2H), 3.11 (t, J = 4.6 Hz, 4H), 2.63 (br s, 4H), 2.36 (s, 3H) .
