According to the procedure given for 210f, 209b (14.5 g, 31.1 mmol) was saponified with KOH (85%, 7.2 g, 108.6 mmol) in water (15 mL) and ethanol (45 mL) at reflux for 6 h. After the usual extractive workup, the crude material was purified by flash chromatography (silica gel; ethyl acetate/hexanes=1/20, 1/10, 1/2) to give 210b (4.0 g, 31%) as a white solid. Mp 44-46° C. 1H NMR (CDCl3): 10.25 (br., 2H), 7.35-7.22 (m, 10H), 2.32 (m, 4H), 1.94-1.86 (m, 4H), 1.57 (s, 6H), 1.51-1.22 (m, 4H). 13C NMR (CDCl3): δ 210.64, 182.66, 142.69, 128.66, 127.18, 126.29, 50.07, 42.97, 38.62, 22.20, 19.11. HRMS (LSIMS, gly): Calcd for C25H31O5 (MH+): 411.2171, found: 411.2144. HPLC: 95.2% pure.
