In a 100 mL round-bottomed flask equipped with a reflux condenser tube and a magnetic stirrer, p-hydroxybenzaldehyde (35 g, 287 mmol) and 1-bromobutane (30.92 mL, 287 mmol) were dissolved in N,N-dimethylformamide (DMF, 750 mL). The reaction mixture was stirred for 20 min under nitrogen protection. Subsequently, anhydrous potassium carbonate (118.83 g, 860 mmol) was added and the reaction was continued to be stirred at 70 °C for 20 hours. After completion of the reaction, the mixture was cooled to room temperature. The reaction was quenched with excess water and extracted with ethyl acetate. The organic phases were combined, washed several times with water, dried over anhydrous sodium sulfate and filtered. The crude product was purified by silica gel column chromatography (petroleum ether/ethyl acetate, 20:1) to afford the brown oily target product 4-butoxybenzaldehyde. Yield: 95%; 1H NMR (500 MHz, CDCl3) δH (ppm): 9.89 (s, 1H), 7.84 (d, J = 8.8 Hz, 2H), 7.00 (d, J = 8.6 Hz, 2H), 4.06 (t, J = 6.3 Hz, 2H), 1.79-1.85 (m, 2H), 1.49-1.57 (m. 2H), 1.01 (t, J = 7.3 Hz, 3H); 13C NMR (125 MHz, CDCl3) δC (ppm): 190.7, 164.2, 131.9, 129.8, 114.7, 68.1, 31.0, 19.1, 13.7; ESI-MS: m/z 179.2 ([M + H]+). The following alkoxybenzaldehyde derivatives 4b-h were synthesized by a similar method.
