[Br:1][C:2]1[CH:7]=[CH:6][C:5]([CH:8]2[C:12](=[O:13])[CH:11]=[CH:10][CH:9]2[OH:14])=[C:4]([CH2:15][CH3:16])[CH:3]=1.S(=O)(=O)(O)O.C(O)(C)C>CC(C)=O.[O-2].[O-2].[O-2].[Cr+6]>[Br:1][C:2]1[CH:7]=[CH:6][C:5]([CH:8]2[C:12](=[O:13])[CH:11]=[CH:10][C:9]2=[O:14])=[C:4]([CH2:15][CH3:16])[CH:3]=1To a solution of 5-(4-bromo-2-ethylphenyl)-4-hydroxycyclopent-2-enone (10.14 g, 0.036 mol) in acetone (150 ml) at 5° C. is added chromium trioxide in concentrated sulfuric acid (24 ml, 0.039 mol, 1.64M solution), at such a rate as to maintain a temperature between 10° C. to 15° C. The reaction mixture is further stirred at room temperature for 30 minutes, followed by the addition of isopropanol (150 ml) and additional stirring at room temperature for 2 hours. The green suspension is partitioned between ethyl acetate (200 ml) and water (300 ml), and the organic layer is separated. After drying over anhydrous magnesium sulfate, solvents are removed in vacuo to afford 2-(4-bromo-2-ethylphenyl)cyclopent-4-ene-1,3-dione as an orange gum.
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