(47). was added, and the mixture was stirred at 80 °C for 1 h. After cooling, the mixture was extracted three times with CH2Cl2. 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 solubilized in acetic anhydride (50 mL) and the mixture was stirred at 80 °C for 1.5 h. After cooling, the mixture was concentrated under reduced pressure. The residue was purified by column chromatography on silica gel (eluent CH2Cl2) to afford 55 (6.48 g, 33%) as a brown solid.