Acid catalyzed rearrangements in the arylimino indoline series. Part IV. Reactions of 1,2‐dihydro‐2‐phenyl‐2‐(indol‐3‐yl‐derivatives)‐3‐phenylimino‐3H‐indole with trichloroacetic and hydrochloric acids. Crystal structure of 1,2‐dihydro‐2‐phenyl‐2‐(indol‐3‐yl)‐3‐phenylimino‐3H‐indole

Abstract

Abstract2‐Phenyl‐3‐phenylimino‐3H‐indole reacts with indole, 2‐methylindole and 1,2‐dimethylindole in the presence of stoichiometric trichloroacetic acid to form 1,2‐dihydro‐2‐phenyl‐2‐(indol‐3‐yl‐derivatives)‐3‐phenylimino‐3H‐indole, which during a longer period of time (16 hours) undergoes indolyl transposition to carbon‐3 and elimination of aniline affording the 3,3′‐bis‐indolyls. In the case of 1,2‐dimethylindole the intermediate coming from the indolyl migration may undergo a nucleophilic addition to carbon‐2 of another molecule of indole; the new intermediate leads to the formation of 2‐phenyl‐3,3′‐di‐(1,2‐dimethylindol‐3‐yl)‐3H‐indole by elimination of aniline and migration to carbon‐3 of the second molecule of indole. By treatment with hydrochloric acid in refluxing ethanol, 1,2‐dihydro‐2‐phenyl‐2‐(indol‐3‐yl‐derivatives)‐3‐phenylimino‐3H‐indole afford to 3,3′‐bis‐indolyls and 1,2‐dihydro‐2‐phenyl‐2‐(indol‐3‐yl‐derivatives)‐3H‐indol‐3‐one (indoxyls). The crystal structure of 1,2‐dihydro‐2‐phenyl‐2‐(indol‐3‐yl)‐3‐phenylimino‐3H‐indole is also reported. The latter compound does not give rearrangement products by acid treatment, only untreatable tarry material.