The general procedure for the synthesis of benzofuran-5-sulfonyl chloride using 5-bromobenzofuran as starting material was as follows: isopropyl iodide (15.0 mmol) was slowly added dropwise to a suspension of tetrahydrofuran (25 mL) containing iodine (0.12 mmol) and magnesium scrapings (30.0 mmol) under nitrogen protection. After the dropwise addition, the reaction mixture was stirred at room temperature for 15 min. Subsequently, a tetrahydrofuran (25 mL) solution of 5-bromobenzofuran (15.2 mmol) was added dropwise and the reaction system was heated to reflux and maintained for 1 hour. Upon completion of the reaction, the mixture was cooled to -30°C and sulfonyl chloride gas was passed into it for 10 minutes. After maintaining this temperature for 30 minutes, sulfuryl chloride (15.1 mmol) was slowly added dropwise while ensuring that the reaction temperature was maintained between -30 and -40°C. The reaction temperature was maintained at -30°C for 10 minutes. After the dropwise addition, stirring was continued at -30°C for 10 minutes, after which the reaction mixture was allowed to warm slowly to room temperature. The reaction mixture was filtered to remove insoluble solids and the filtrate was concentrated under reduced pressure. The concentrated residue was dissolved in dichloromethane (150 mL), washed sequentially with saturated saline (3 x 100 mL), and the organic phase was dried with anhydrous sodium sulfate, filtered and concentrated under reduced pressure. Finally, the target product benzofuran-5-sulfonyl chloride was purified by fast column chromatography (eluent ratio: petroleum ether/ethyl acetate = 100/1 to 50/1) to give 15% yield as a white solid. The product was identified by 1H NMR (CDCl3): δ 8.37 (s, 1H), 8.00 (d, 1H), 7.84 (s, 1H), 7.44 (d, 1H), 6.97 (s, 1H). m/z 286 [M + BnH-1]+ was shown by LC/MS (ES) analysis.
