To a stirred solution of 1-(toluene-4-sulfonyl)-4-(toluene-4-sulfonyloxy)-pyrrolidine-2-carboxylic acid ethyl ester (2) (1 g, 2.14 mmol) in dry DMF (25 mL) is added potassium acetate (0.314 g, 3.21 mmol) in one portion. The reaction mixture is then heated at 60° C. for 4 h. Water (50 mL) is added to the reaction mixture and extracted with ethyl acetate (2×75 mL), combined organic layer are washed with water (2×50 mL), dried (Na2SO4), filtered, and concentrated under reduced pressure to give the crude compound. Crude compound is purified by column chromatography over silica gel (100-200 mesh) using 15% ethyl acetate-hexane as eluent to give compound (3).
