A solution of diisopropylazodicarboxylate (0.81 g, 4.0 mmol) in dry THF (2 ml) was added to a stirred solution of episarsasapogenin (0.83 g, 2.0 mmol), triphenylphosphine (1.05 g, 4.0 mmol) and benzoic acid (0.49 g, 4.0 mmol) in dry THF (20 ml). The mixture was stirred at room temperature and monitored by TLC. After 2 h all the starting material had been consumed. The solvent was removed in vacuo, the residual syrup dissolved in ether (30 ml) and the solution washed with aqueous saturated sodium hydrogen carbonate (25 ml). The organic layer was dried over MgSO4 and passed down a short silica pad, the pad being washed with ether. The combined washings and filtrate were concentrated in vacuo to afford sarsasapogenin benzoate as a white solid.
