O.[OH-].[Li+].C([O:6][C:7]([C:9]1[CH:13]=[CH:12][N:11]([C:14]2[CH:23]=[CH:22][C:21]3[C:16](=[CH:17][CH:18]=[CH:19][CH:20]=3)[N:15]=2)[C:10]=1[CH3:24])=[O:8])C.Cl>O1CCCC1.O>[C:7]([C:9]1[CH:13]=[CH:12][N:11]([C:14]2[CH:23]=[CH:22][C:21]3[C:16](=[CH:17][CH:18]=[CH:19][CH:20]=3)[N:15]=2)[C:10]=1[CH3:24])([OH:8])=[O:6]3.9 g (93 mmol) of lithium hydroxide monohydrate, portionwise every 24 hours, are added at 20° C. to 1.9 g (6.78 mmol) of 3-ethoxycarbonyl-2-methyl-1-(quinol-2-yl)-1H-pyrrole dissolved in 50 mL of tetrahydrofuran and 50 mL of water. After stirring at reflux for 72 hours, the reaction mixture is concentrated to dryness under reduced pressure (2.7 kPa) to give a residue that is taken up in 75 mL of water. The pH of the aqueous phase is adjusted to 2 by addition of concentrated hydrochloric acid. After stirring for 1 hour, the aqueous phase is filtered and the solid residue is dried under reduced pressure (2.7 kPa) at 40° C. to give 1.9 g of 3-carboxy-2-methyl-1-(quinol-2-yl)-1H-pyrrole in the form of a beige-coloured solid.
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