Synthesis of 7-bromo-2,3-dihydrobenzofuran: In a dry reaction flask, 1,3-dibromo-2-(2-bromoethoxy)benzene (11.5 g, 32.0 mmol) was dissolved in a mixed solvent of 115 mL of anhydrous THF and 28 mL of hexane. The reaction system was cooled to -78 °C under nitrogen protection, and 2.5 M n-butyllithium (n-BuLi, 13.0 mL, 32.5 mmol) solution was slowly added dropwise for a controlled time of 30 min. After the dropwise addition was completed, the reaction was kept at -78 °C for 30 min and then the reaction system was slowly warmed up to 0 °C. After completion of the reaction, the mixture was carefully poured into 100 mL of ice water and the aqueous phase was extracted with ether (3 x 50 mL). The organic layers were combined, dried with anhydrous sodium sulfate (Na2SO4), filtered and concentrated under reduced pressure to give a light yellow oily crude product. The crude product was purified by silica gel column chromatography with gradient elution of ethyl acetate/hexane to afford colorless needle-like crystals of 7-bromo-2,3-dihydrobenzofuran (5.00 g, 78% yield). The structure of the product was confirmed by 1H NMR (500 MHz, DMSO-d6): δ 7.27 (dd, J=1,8Hz, 1H), 7.20 (dd, J=1,7.5Hz, 1H), 6.75 (t, J=7.8Hz, 1H), 4.59 (t, J=9Hz, 2H), 3.28 (t, J=8.8Hz, 2H).
