[C:1]1([C:6]([C:8]2[N:12]3[CH2:13][CH2:14][CH:15]([C:16]([O:18]C(C)C)=[O:17])[C:11]3=[CH:10][C:9]=2[CH3:22])=[O:7])[S:5][CH:4]=[CH:3][CH:2]=1.CO.C(=O)([O-])[O-].[K+].[K+]>O>[C:1]1([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][C:9]=2[CH3:22])=[O:7])[S:5][CH:4]=[CH:3][CH:2]=1A solution of 500 mg. of isopropyl 5-(2-thenoyl)-1,2-dihydro-6-methyl-3H-pyrrolo[1,2-a]pyrrole-1-carboxylate in 15 ml. of methanol is treated with a solution of 1.05 g. of potassium carbonate in 8 ml. of water. The reaction mixture is refluxed under nitrogen atmosphere for 3 hours, 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 (3 × 50 ml.). The combined extracts are dried over magnesium sulfate and evaporated to dryness under reduced pressure, to give 5-(2-thenoyl)-1,2-dihydro-6-methyl-3H-pyrrolo[1,2-a]pyrrole-1-carboxylic acid [(A), R = CH3, R1 = H, X = S], having a melting point of 166° C.
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