(3R,4S)-6-Acetyl-4-(3,5-difluorobenzamido)-3,4-dihydro-2,2-dimethyl-3-hydroxy-2H-1-benzopyran D3 (1.88 g, 5.0 mmol) (Example 4 of WO95/34545) was dissolved in acetonitrile (25ml), water (5 ml) and trifluoroacetic acid (0.77 ml, 10.0 mmol). [Bis(trifluoroacetoxy)iodo]benzene (4.30 g, 10.0 mmol) was added and the reaction stirred under reflux for three hours. The reaction mixture was allowed to cool and the acetonitrile was removed in vacuo, the resulting material being partitioned between water (50 ml) and dichloromethane (125 ml). The aqueous layer was extracted with further portions of dichloromethane (3×25 ml) and the combined organic extracts were dried over magnesium sulphate, filtered and the solvent removed in vacuo. The resulting yellow solid was purified by column chromatography on silica, eluting with 20% to 40% ethyl acetate in hexane to afford the title compound as a white solid (0.70 g, 36%, m.p. 179.4° C.).
