O.[OH-].[Li+].O.C[O:6][C:7]([C:9]1[CH:13]=[CH:12][N:11]([C:14]2[CH:23]=[CH:22][CH:21]=[C:20]3[C:15]=2[CH:16]=[CH:17][CH:18]=[N:19]3)[CH:10]=1)=[O:8]>O1CCCC1>[C:7]([C:9]1[CH:13]=[CH:12][N:11]([C:14]2[CH:23]=[CH:22][CH:21]=[C:20]3[C:15]=2[CH:16]=[CH:17][CH:18]=[N:19]3)[CH:10]=1)([OH:8])=[O:6]0.36 g (8.58 mmol) of lithium hydroxide monohydrate and 20 mL of water are added to a solution at a temperature in the region of 22° C. of 0.5 g (1.98 mmol) of 3-methoxycarbonyl-1-(quinol-5-yl)-1H-pyrrole in 20 mL of tetrahydrofuran. After stirring at the reflux point of the solvent for 15 hours, the reaction mixture is concentrated to dryness under reduced pressure (2.7 kPa) and the residue is taken up in water. The resulting solution is adjusted to pH 7 using N hydrochloric acid and then it is extracted with ethyl acetate. The organic phase is washed with a saturated sodium chloride solution, dried over magnesium sulphate, filtered and concentrated to dryness under reduced pressure (2.7 kPa). 0.42 g of 3-carboxy-1-(quinol-5-yl)-1H-pyrrole is thus obtained in the form of a white solid. IR spectrum (KBr): 3423, 3105, 1665, 1536, 1275, 1188, 1107, 965 and 796 cm−1.
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