(1.75 mL, 18.4 mmol) at 0 °C. The solution was stirred at 25 °C for 2 days. Cold water was then added and the suspension was extracted three times with AcOEt. The combined organic layers were washed with water and brine, dried over anhydrous MgSO4, filtered, and the filtrate was concentrated under reduced pressure. The residue was washed with acetone to afford 9 (17 mg, 6%) as a black solid.