Acetyl chloride → 1-(3,4-dihydro-2H-1-benzopyran-6-yl)ethan-1-one

Aluminium chloride (1.19 g, 8.9 mmol) was added portionwise to a stirred solution of acetyl chloride (1.21 mL, 17.0 mmol) in dry dichloromethane (20 mL), previously cooled to −10° C., until homogeneous (5 min). The solution was added, via cannula, to a solution of 3,4-dihydro-2H-1-benzopyran (9a) (1.20 g, 8.9 mmol) in dry dichloromethane (17 mL) at −10° C. The mixture was stirred at the same temperature for 30 minutes before being poured into ice/concentrated hydrochloric acid (5:1, v/v, 126 mL). The stirring was maintained at room temperature for 2 hours and the solution was extracted with dichloromethane (3×50 mL). The organic layer was dried over sodium sulfate and concentrated in vacuo to provide 1-(3,4-dihydro-2H-1-benzopyran-6-yl)ethan-1-one (49a) (1.55 g, 8.8 mmol, 99%) which was used without further purification.