General procedure for the synthesis of benzo[b]furan-2-carbaldehyde from 2,3-benzofuran and N,N-dimethylformamide: Triclosan (4.73 mL, 50.79 mmol) was slowly added to a solution of N,N-dimethylformamide (6.56 mL, 84.75 mmol) under conditions of keeping the temperature lower than 40 °C. Subsequently, 2,3-benzofuran (2.00 g, 16.93 mmol) was added dropwise to the reaction mixture over a period of 15 min under the same temperature conditions. The reaction mixture was heated up to 80 °C for 24 hours. After completion of the reaction, the mixture was carefully poured into ice water and neutralized with sodium hydroxide solution. The organic phase was separated and the aqueous phase was extracted with ethyl acetate. The organic phases were combined, washed with brine and dried over anhydrous magnesium sulfate. The filtrate was concentrated under reduced pressure and the resulting crude product was purified by silica gel column chromatography (eluent: petroleum ether/ethyl acetate = 10:1) to afford benzo[b]furan-2-carbaldehyde (2.27 g, 90% yield) as a brown oil.1H NMR (400 MHz, CDCl3): δ 9.83 (1H, s, CHO), 7.75-7.70 (1H, m, H-4 ), 7.56-7.54 (2H, m, H-6,7), 7.46 (1H, s, H-3), 7.32-7.28 (1H, m, H-5).13C NMR (100 MHz, CDCl3): δ 179.63 (CHO), 156.03 (C-7a), 152.52 (C-2), 129.07 (C-3a) , 126.51 (C-6), 124.05 (C-5), 123.58 (C-4), 117.93 (C-3), 112.44 (C-7).
