5-Nitroindole-2-carboxylic acid

Nitroindole-2-carboxylic acid (0.86 g), l-[3-(N-isopropyl)amino-2-pyridinyl]piperazine (0.43 g), l-(ethyl)-3-(dimethylaminopropyl)carbodiimide (0.45 g) and THF (4 ml), were stirred at 20-25°C for 3 hr then the reaction mixture was dissolved in chloroform (50 ml) and extracted with saturated aqueous sodium bicarbonate, saline, dried over anhydrous sodium sulfate and concentrated under reduced pressure. Purification by flash column chromatography (200 g silica) eluting with ethyl acetate/hexane (50/50), the appropriate fractions were pooled and concentrated to give l-[5-nitroindolyl-2-carbonyl]-4-[3-(l-methylethylamino)-2-pyridinyl]piperazine, mp 153°-154°C. 

In the previous review (91YGK205, 99H1157), we reported that l-hydroxy-4-nitroindole forms active ester derivatives by reaction with carboxylic acids, which can be applied to acylation of various nucleophiles. To expand the scope of the reaction and obtain novel fungicidal compounds, an attempt has been made to prepare derivatives of wasabi phytoalexin 109 (98P1959). 

C9H5CIF6 3,5-bis(lrifluoromethyl)benzyi chloride 75462-59-8 25.00 1.4425 2 15920 C9H6N204 7-nitroindole-2-carboxylic acid 6960-45-8 25.00 1.4621 2... 

Decarboxylation (solvent effect). Casini and Cioudman found lhal decarboxylation of 7-nitroindole-2-carboxylic acid by heating with a catalytic amount of the copper salt of the acid proceeded in higher yield and with simpler isolation of product when N,N-dimethylacetamide was used as solvent rather than the conventional quinoline. 

Nitroindole-2-carboxylic acid refluxed under Ng in the presence of its cupric salt in N,N-dimethylacetainide until after ca. 5 hrs. COg-evolution ceases 7-nitroindole. Y 89%.—With N,N-dimethylacetamide as medium, the yield is higher and the isolation of the product simpler than with the usually used quinoline. G. Gasini and L. Goodman, Gan. J. Ghem. 42, 1235 (1964). 

Nitrophenyl hydrazones of ketones reacted similarly. On heating aryUiydrazones of pyruvic ester 192 with polyphosphoric acid (PPA), mixtures of ethyl 4- and 6-nitroindole-2-carboxylates were formed [145, 146] (Scheme 95). 

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