[CH3:1][CH2:2][O:3][C:4]([C@H:6]1[CH2:10][C@H:9]([Se]C2C=CC=CC=2)[CH2:8][N:7]1[C:18]([O:20][C:21]([CH3:24])([CH3:23])[CH3:22])=[O:19])=[O:5].N1C=CC=CC=1.OO>ClCCl>[CH3:1][CH2:2][O:3][C:4]([C@H:6]1[CH:10]=[CH:9][CH2:8][N:7]1[C:18]([O:20][C:21]([CH3:22])([CH3:24])[CH3:23])=[O:19])=[O:5]To a solution of 7.35 g (0.016 mol) (2R,4S)-4-phenylselanyl-pyrrolidine-1,2-dicarboxylic acid 1-tert-butyl ester 2-ethyl ester in 80 ml dichloromethane were added at 0-5° C. 1.93 ml (0.024 mol) pyridine and 4.6 ml 30% hydrogen peroxide and stirring was continued for 1.5 hours. The mixture was extracted with 5% aqueous HCl, saturated aqueous sodium carbonate, and water. Chromatography on silicagel with ethylacetate/hexane 1:5 yielded 2.99 g (77%) (R)-2,5-dihydro-pyrrole-1,2-dicarboxylic acid 1-tert-butyl ester 2-ethyl ester as colorless oil. MS m/e (%): 186 (11), 168 (48), 140 (32), 112 (100), 68 (85), 57 (58). [α]D=+242° (c=1% in chloroform).
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