The general procedure for the synthesis of 4-diethylamino-2-methoxy-benzaldehyde from 4-(diethylamino)salicylaldehyde and iodomethane was as follows: 4-diethylamino-2-hydroxybenzaldehyde (5.8 g, 30 mmol), potassium hydroxide (2 g, 35 mmol), and potassium carbonate (8.3 g, 60 mmol) were dissolved in acetonitrile (30 mL), and heated and stirred at 80 °C for for 10 min. Subsequently, iodomethane (3.5 mL, 56 mmol) was slowly added to the reaction system, and the reaction continued to be stirred at 80 °C for 2 hours. After completion of the reaction, the mixture was cooled to room temperature and filtered to remove insoluble impurities. The filtrate was concentrated under reduced pressure and purified by silica gel column chromatography (sieve size 120-200 mesh) with the eluent ethyl acetate/hexane (1:3, v/v) to afford the target product 4-diethylamino-2-methoxy-benzaldehyde as a yellow solid in 85% yield. The structure of the product was confirmed by 1H NMR and 13C NMR: 1H NMR (500 MHz, CDCl3) δ 10.11 (s, 1H), 7.68 (dd, J = 8.9, 2.8 Hz, 1H), 6.26 (d, J = 8.8 Hz, 1H), 6.02 (s, 1H), 3.87 (s, 3H), 3.41 (dd, J = 6.9, 2.7 Hz, 4H), 1.21 (t, J = 5.4 Hz, 6H); 13C NMR (125 MHz, CDCl3) δ 187.1, 164.1, 153.8, 130.7, 114.2, 104.2, 92.4, 55.2, 44.7, 12.5.
