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Preparation of 5 was based on a procedure for the synthesis of indole-3-carboxylic acid reported by R. K. Mackie et al. [supra]. To a 200-mL round bottom flask, 2.369 g of 4 (9.75 mmol) was added. Compound 4 was dissolved in 19 mL of absolute ethanol and 53 mL of 5N aqueous sodium hydroxide, refluxed overnight, and allowed to cool. The ethanol was removed by rotary evaporation, and the resulting solution was extracted with two 25-mL portions of diethyl ether. The aqueous solution was acidified with concentrated hydrochloric acid, and the peach-colored precipitate was collected. Recrystallization from hot aqueous ethanol (50:50 ethanol:water) yielded 0.883 g (47%) of 5 as cream-colored crystals: 1H NMR (acetone-d6) δ 3.95 (s, 3H, OCH3), 6.76 (d, 1H, J=7.3 Hz), 7.10 (app. t, 1H, J=8 Hz), 7.71 (d, 1H, J=8.5 Hz), 7.95 (m, 1H), 11.0 (br s, 1H).

1. customPreparation of 5
2. temperatureto cool
3. customThe ethanol was removed by rotary evaporation
4. extractionthe resulting solution was extracted with two 25-mL portions of diethyl ether
5. customthe peach-colored precipitate was collected
6. customRecrystallization from hot aqueous ethanol (50:50 ethanol:water)