4.2 g (9.2 mmol) of 5b were dissolved in 120 ml of t-BuOH. 50 ml of 50% aq. KOH were added, and the mixture was then boiled at 100° C. for 24 hours. For work-up, the mixture was allowed to cool and then diluted with 100 ml of ethyl acetate. The aqueous phase was made slightly acidic by addition of 2 N aqueous HCl and extracted 2 more times with 100 ml of ethyl acetate. The organic phase was dried over MgSO4, filtered and concentrated, and the residue was purified by flash chromatography (methylene chloride/methanol/conc. ammonia, 30/5/1). This gave 6b as a white amorphous solid. TLC (methylene chloride/methanol/conc. ammonia, 30/5/1). Rf=0.3. Recrystallization from toluene. C25H26FNO5 (432.42) MS(ESI): 433 (M+H+).
