The general procedure for the synthesis of 2,3-dihydrobenzofuran-4-carbaldehyde from 4-hydroxymethyl-benzodihydrofuran was as follows: a dichloromethane solution (40 mL, 2 M) of oxalyl chloride was stirred at -78 °C and DMSO (8.10 mL, 114 mmol) was slowly added. Subsequently, a dichloromethane solution (35 mL) of 4-hydroxymethyl-benzodihydrofuran (8.53 g, 56.9 mmol) was added dropwise and stirring was continued for 30 min at -78 °C. Upon completion of the reaction, triethylamine (33 mL, 228 mmol) was carefully added to quench the reaction. The resulting suspension was stirred at room temperature for 30 min and then diluted with dichloromethane (100 mL). The organic layer was washed three times with water and twice with brine sequentially, and finally concentrated by vacuum to give 2,3-dihydrobenzofuran-4-carbaldehyde as an oil (8.42 g, 100%), which could be used for subsequent reactions without further purification.
