To a solution of the product from Example 9B (0.396 g, 1.0 mmol) in DMF (10 mL) at room temperature was added pyridinium dichromate (2.3 g), and the mixture was stirred for 48 hours. 10% citric acid was added and the reaction was extracted twice with ethyl acetate. The combined organic layer was washed with brine, dried over MgSO4, filtered and evaporated. The residue was purified by chromatography on silica gel, eluting with a gradient of 0-5% methanol in chloroform, to give the title compound (0.334 g, 81%).
