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With water; sodium hydroxide; In methanol; at 60℃;
A 40-mL vial was charged with ethyl 5,7-dichloro-lH-indole-2-carboxylate (516 mg, 2.00 mmol, 1.00 equiv), MeOH (1 mL), water (5 mL) and sodium hydroxide (120 mg, 3.00 mmol, 1.50 equiv). The resulting solution was stirred overnight at 60 C. The volume of the solution was concentrated to reduce by half. Then the pH value was adjusted to 4-5 with aqueous hydrochloric acid (1 mol/L), resulting in the precipitation of a solid. The solid was collected by filtration, washed with water (3 x 10 mL), and dried to provide 294 mg (64% yield) of 5,7-dichloro-lH-indole-2-carboxylic acid as a light brown solid. LCMS (ESI, m/z): 228 [M-
In methanol; sodium hydroxide;
C. 5,7-Dichloro-1H-indole-2-carboxylic acid A solution of <strong>[4792-70-5]ethyl 5,7-dichloro-1H-indole-2-carboxylate</strong> (0.80 g, 3.1 mmol) in 1 N NaOH (40 mL) and methanol (50 mL) was heated to reflux for 3 hours. The methanol was removed in vacuo and the aqueous residue was acidified with 1 N HCl and extracted with chloroform twice. The combined extracts were washed with water and brine, dried over magnesium sulfate and concentrated to a solid (0.58 g, 76%). The following indole carboxylic acids were prepared by the same sequence: 4-Chloro-5-fluoro-1H-indole-2-carboxylic acid and 6-chloro-5-fluoro-1H-indole-2-carboxylic acid (as a mixture) from 3-chloro4-fluorophenylhydrazine. 5,7-Difluoro-1H-indole-2-carboxylic acid from 2,4-difluorophenylhydrazine
In methanol; sodium hydroxide;
C. 5,7-Dichloro-1H-indole-2-carboxylic acid A solution of <strong>[4792-70-5]ethyl 5,7-dichloro-1H-indole-2-carboxylate</strong> (0.80 g, 3.1 mmol) in 1 N NaOH (40 mL) and methanol (50 mL) was heated to reflux for 3 hours. The methanol was removed in vacuo and the aqueous residue was acidified with 1 N HCl and extracted with chloroform twice. The combined extracts were washed with water and brine, dried over magnesium sulfate and concentrated to a solid (0.58 g, 76 %). The following indole carboxylic acids were prepared by the same sequence: 4- Chloro-5-fluoro-1H-indole-2-carboxylic acid and 6-chloro-5-fluoro-1H-indole-2-carboxylic acid (as a mixture) from 3-chloro-4-fluorophenylhydrazine.
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