Organocatalytic Reactions of Indoles with Quinone Imine Ketals: An Alternative Metal‐Free Approach to Bioactive <i>meta</i>‐Indolylanilines

Abstract

Abstract An organocatalytic metal‐free strategy has been established for the synthesis of pharmaceutically relevant meta ‐indolylanilines in generally excellent yields (up to 99 %). This strategy took advantage of the reaction of indoles and quinone imine ketals (QIKs) in the presence of racemic phosphoric acid, which proceeded via a 1,4‐addition/alcohol elimination reaction sequence. The control experiment demonstrated that the dual hydrogen‐bonding activation mode of the catalyst to the substrates played a crucial role in the reaction. This protocol provides a metal‐free and step‐economical approach to meta ‐anilines bearing either 3‐indolyl or 2‐indolyl moiety, which is of high value for the synthesis of compounds with potential bioactivities. magnified image