Lewis acid-catalyzed cascade via intercepted Meyer–Schuster O-allenylation and [3,3]-sigmatropic rearrangement: divergent synthesis of 2-alkenylanilines and indoles

Abstract

A Lewis acid-catalyzed cascade reaction has been developed for the synthesis of 2-alkenylaniline derivatives bearing an enone moiety. This method utilizes readily available N-aryl hydroxyamines and propargylic alcohols under mild conditions. The mechanism likely involves an intercepted Meyer–Schuster O-allenylation via S_N1′ reaction, followed by a [3,3]-sigmatropic rearrangement/rearomatization sequence. When PMHS is introduced as a reducing agent, the enone intermediates undergo in situ reduction, followed by cyclization and elimination, enabling a one-pot synthesis of polysubstituted indoles. The reaction demonstrates broad functional group tolerance and offers a practical route to a wide range of multifunctionalized anilines, enones, and indoles in good yields.