Hydrochloric Acid → 4,5-dichloro-1H-indole-2-carboxylic acid

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Reaction Steps

4,5-Dichloro-1H-indole-2-carboxylic acid ethyl ester (0.5 g) was treated with 1 M lithium hydroxide in ethanol (3 mL) and heated, water bath, for 2 h. The solution was acidified with 10% hydrochloric acid, diluted with water and extracted with ethylacetate. The organic extracts were combined, dried over sodium sulfate and filtered, and solvent was evaporated to give 4,5-dichloro-1H-indole-2-carboxylic acid (0.27 g, 60%). This material was treated with -ethyl-3-(3′-dimethylaminopropyl)-carbodiimide hydrochloride (0.5 g), HOBT (0.4 g) and N,N-diisopropylethylamine (1 mL) in DMF (2 mL) and dichloromethane (2 mL) was treated with N-methylpiperazine (0.2 mL) stirred at ambient temperature for 18 h then diluted with water. The organic portion was separated, washed with brine, dried over sodium sulfate, and filtered. Solvent was removed under reduced pressure, and the residue was purified via silica gel chromatography (3-8% 2 M ammonia in methanol/dichloromethane) to give the title compound (0.15 g, 40%). 1H NMR (400 MHz, CDCl3): δ 10.2 (br.s, 1H), 7.25-7.16 (m, 2H), 6.75 (d, J=2 Hz, 1H), 3.92 (br.m, 4H), 2.47 (m, 4H), 2.30 (s, 3H). MS (electrospray): exact mass calculated for C14H15Cl2N3O, 311.06; m/z found, 312.0 [M+H]+.

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