[C:1]1([S:7]([CH2:10][C:11]2[O:12][C:13]([CH3:16])=[N:14][N:15]=2)(=[O:9])=[O:8])[CH:6]=[CH:5][CH:4]=[CH:3][CH:2]=1.C[O-].[Na+].[C:20]1(=[O:25])[CH2:24][CH2:23][CH:22]=[CH:21]1>CO.[NH4+].[Cl-]>[C:1]1([S:7]([CH:10]([C:11]2[O:12][C:13]([CH3:16])=[N:14][N:15]=2)[CH:22]2[CH2:23][CH2:24][C:20](=[O:25])[CH2:21]2)(=[O:9])=[O:8])[CH:2]=[CH:3][CH:4]=[CH:5][CH:6]=1
To 650 mg (2.73 mmol) of 2-benzenesulfonylmethyl-5-methyl-[1,3,4]oxadiazole in 35 mL of MeOH at 0° C., 50 μL (0.27 mmol, 0.1 eq) of a solution of sodium methoxide (5.4 M in MeOH) were added. After 15 min, 246 mg (3.0 mmol, 1.1 eq) of cyclopent-2-enone were added. The reaction mixture was stirred at 0° C. and was allowed to reach RT within 4 hours, diluted with saturated aqueous NH4Cl and extracted with EtOAc. The combined organic phases were dried over Na2SO4, filtered and evaporated. Column chromatography on silica gel with EtOAc gave 750 mg (86%) of 3-[benzenesulfonyl-(5-methyl-[1,3,4]oxadiazol-2-yl)-methyl]-cyclopentanone as a racemic mixture of diastereomers, white solid, MS: 321 (MH+).
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