Isatinic acids

Isatin is the inner anhydride (lactam) of a y-amino-a-ketocarboxylic acid, isatinic acid (A), and is converted into a salt of this acid by the action of alkali. The keto-group in position 3 can condense with many other substances, and for this reason isatin is manufactured on a technical scale and converted into valuable indigoid vat dyes. The magnificent thioindigo scarlet, which is obtained from isatin and a sulphur analogue of indoxyl (the so-called hydroxythionaphthene), may be taken as example qq... 

Since the Pfitzinger reaction requires a large excess of alkali, aliphatic aldehydes, which readily polymerize under these conditions, cannot be used in the reaction. However, it was possible to overcome these difficulties by using the aldoximes. Thus, Pfitzinger heated the isatin 7 with acetaldehyde oxime in the presence of potassium hydroxide in water and obtained 4-quinolinecarboxylic acid together with the oxime of isatinic acid 196 [175],... 

Iron (III) nitrate, anhydrous 1737 IsatInIc acid anhydride 2068... 

Indole-2,3-dione (isatin), red crystals, mp 204°C, is formed by the oxidation of indigo with nitric acid. It can be synthesized from o-nitrobenzoyl chloride via isatinic acid 45 ... 

The alkali first converts isatin into the salt 69 of isatinic acid which, being a carbonyl compound, cyclocondenses via the a-keto function with methylene ketones to give derivatives of quinoline-4-carboxylic acid [100]. 

Aminoketocarboxylic acids s. Isatinic acids Aminoketones (s. a. Halogen-aminoketones)... 

Isatic Acid o-Aminobenzoylformic acid, o-aminophenylglyoxylic add, isatinic acid) CO-COOH... 

Quinazoline-4-carboxylic acids from isatinic acids... 

In the alkaline medium, isatin is cleaved at the amide bond and converted to the salt 82 of isatinic acid, which undergoes aldol condensation with a-methylene ketones and cyclization with H2O elimination affording quinoline-4-carboxyhc acids (83). Notably, N-acetylisatins (84), after base-induced ring-opening (— -85), undergo an intramolecular aldol condensation giving rise to 2-quinolone-4-carboxylic acids (86). 

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