Bis(indolyl-3-)phthalides and their spectral properties

Symmetrical bis-indolylphthalides, having electron-releasing and electron-withdrawing substituents on the indole rings, were obtained from the reaction between an indole and an unsubstituted or substituted phthalic anhydride. Unsymmetrical indolylphthalides were synthesized by the condensation of 3-(o-carboxybenzoyl)indole with a substituted indole. A relationship was found to exist between the nature of the substituent, and the spectral and acid-base properties of the compounds.