A mixture of pyridinium chlorochromate (PCC, 29 g) and silica gel (29 g) was prepared, dissolved in CH2Cl2 (200 mL) and stirred vigorously. A solution of 5 (18 g, 0.089 mol) in CH2Cl2 (300 mL) was added slowly over 1 hour. The reaction was allowed to stir at room temperature for 18 hours and monitored by TLC until the starting material was consumed. The reaction mixture was added directly to a silica gel column (400 g, 3 inch diameter) and flushed with CH2Cl2.