[F:1][C:2]1[CH:25]=[CH:24][C:5]([C:6]([C:8]2[N:12]3[CH2:13][CH2:14][C:15](C(OC)=O)([C:16]([O:18]C)=[O:17])[C:11]3=[CH:10][CH:9]=2)=[O:7])=[CH:4][CH:3]=1.FC1C=CC(C(C2N3CCC(C(OC)=O)C3=CC=2)=O)=CC=1.[OH-].[K+]>CO.O>[F:1][C:2]1[CH:25]=[CH:24][C:5]([C:6]([C:8]2[N:12]3[CH2:13][CH2:14][CH:15]([C:16]([OH:18])=[O:17])[C:11]3=[CH:10][CH:9]=2)=[O:7])=[CH:4][CH:3]=1A solution of the mixture of dimethyl 5-(4-fluorobenzoyl)-1,2-dihydro-3H-pyrrolo[1,2-a]pyrrole-1,1-dicarboxylate and methyl 5-(4-fluorobenzoyl)-1,2-dihydro-3H-pyrrolo[1,2-a]pyrrole-1-carboxylate (0.200 g) in methanol (5 ml) and water (3 ml) containing potassium hydroxide (0.5 g) was heated at reflux temperature for 1 hour. The solvent was removed in vacuo, water was added to the residue and the solution was made acidic with 10% hydrochloric acid solution. The product was extracted into ethyl acetate, the extract was dried and evaporated. The solid residue on crystallization from ethyl acetate-hexane gave 5-(4-fluorobenzoyl)-1,2-dihydro-3H-pyrrolo[1,2-a]pyrrole-1-carboxylic acid (0.124 g, 80%) m.p. 163°. A mixed m.p. with an authentic specimen (m.p. 170°) had m.p. 165°. The IR spectrum was identical to that of the authentic sample.
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