To a solution of 47 (301 mg, 0.920 mmol) in pyridine (15 mL) was added Hg(OAc)2 (731 mg, 2.30 mmol). The solution was refluxed for 15 h. After cooling, iced water was added and the mixture 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. To a solution of the residue in anhydrous CH2Cl2 (8 mL) was added pure BBr3