Potassium Hydroxide → 4-(2-carboxy-ethyl)-3-methyl-5-(5-methoxy-2-oxo-1,2-dihydroindol-3-ylidenemethyl)-1H-pyrrole-2-carboxylic acid

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A mixture of 5-formyl-4-(2-ethoxycarbonylethyl)-3-methyl-1H-pyrrole-2-carboxylic acid ethyl ester (562 mg), 5-methoxy-2-oxindole (326 mg), and piperidine (2 drops) in ethanol (2 mL) were stirred at 90° C. for 2 hours. Potassium hydroxide (537 mg) was added, the temperature was increased to 95° C. and held there for 1 hour. The reaction mixture was cooled and concentrated. The residue was dissolved into water and acidified with 2 N hydrochloric acid to pH 2. The precipitate was filtered, washed with water, and dried in a vacuum oven overnight to give 240 mg (65%) of 4-(2-carboxy-ethyl)-3-methyl-5-(5-methoxy-2-oxo-1,2-dihydroindol-3-ylidenemethyl)-1H-pyrrole-2-carboxylic acid.

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