To a solution of compound 28n (100 mg, 0.26 mol) in 10 mL of chloroform-ethanol co-solvent (ratio, 4:1) was added tin(II) chloride.dihydrate (293 mg, 1.30 mmol). The reaction mixture was stirred at 45° C. overnight. The reaction mixture was diluted with dichloromethane and washed with sat'd aqueous NaHCO3, collected the organic layer, dried over anhydrous Na2SO4, filtered, concentrated and purified by silica column chromatography (10% ethyl acetate in dichloromethane) to afford 88 mg (97.0%) of pure 28o as a yellow-orange solid.
