Referring to scheme 10, compound 3a (7 g, 19.2 mmol) was dissolved in anhydrous THF and cooled to 0° C. under argon atmosphere. Borane-THF (50 mL, 1M soln. in THF, 2.5 equiv.) was added slowly over a period of 15 mins. The reaction mixture was brought to room temperature and stirred at reflux temperature for over night. After 16 h, the reaction mixture was cooled and concentrated under vacuum to dryness. To the residue, saturated solution of ammonium chloride (200 mL) was added and the product extracted with ethyl acetate (3×100 mL). The combined organic layer was dried over anhydrous sodium sulfate, filtered and concentrated under reduced pressure. The crude was purified by column chromatography over silica gel to afford compound 29 as a viscous liquid (6.2 g, 92%).
