[C:1]([C:9]1[N:13]2[CH2:14][CH2:15][CH:16]([C:17]([O:19]C(C)C)=[O:18])[C:12]2=[C:11]([Br:23])[CH:10]=1)(=[O:8])[C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][CH:3]=1.CO.C(=O)([O-])[O-].[K+].[K+]>O>[C:1]([C:9]1[N:13]2[CH2:14][CH2:15][CH:16]([C:17]([OH:19])=[O:18])[C:12]2=[C:11]([Br:23])[CH:10]=1)(=[O:8])[C:2]1[CH:3]=[CH:4][CH:5]=[CH:6][CH:7]=1A solution of 336 mg. of isopropyl 5-benzoyl-7-bromo-1,2-dihydro-3H-pyrrolo[1,2-a]-pyrrole-1-carboxylate in 10 ml. of methanol is treated with a solution of 690 mg. of potassium carbonate in 5 ml. of water. The reaction mixture is refluxed under nitrogen atmosphere for 30 minitres, cooled, and evaporated to dryness. The residue is taken up in 10 ml. of 10% aqueous hydrochloric acid and 50 ml. of water and the resultant mixture extracted with ethyl acetate (2×50 ml.). The combined extracts are dried over magnesium sulfate and evaporated to dryness under reduced pressure. Crystallization of the residue from ethyl acetate-hexane affords 5-benzoyl-7-bromo-1,2-dihydro-3H-pyrrolo[1,2-a]pyrrole-1-carboxylic acid.
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