SnCl2.2H2O (2.5 g, 11.08 mmol) was added to a stirred solution of compound 30 (2.24 mmol) in ethyl acetate(50 mL) and the resulting mixture heated at reflux for 18 h. The reaction mixture was cooled to ambient temperature and treated with 0.880 SG NH3(aq) dropwise to pH8. The resulting precipitate was removed by filtration through diatomaceous earth (Celite®)(545). The filtrates were then evaporated and purified by chromatography (Mega Bond Elut,Silica), eluting with dichloromethane and then 50% ethyl acetate/i-hexane to give the desired compound 21.
