A mixture of 298c (100 mg, 0.24 mmol), NaBH(OAc)3 (100 mg, 0.48 mmol), HCHO (10 mL) and acetic acid (1 mL) in methanol (15 mL) was stirred at room temperature for 4 h. The solvent was evaporated in vacuo and the residue was neutralized with NaHCO3 solution until pH 8 was reached. The mixture was extracted with ethyl acetate. The combined extracts were dried over sodium sulfate and concentrated under reduced pressure to give 298d (100 mg), which was used for the next step without further purification. MS: [M+H]+ 349.
