Alkylideneindoleninium Ions and Alkylideneindolenines: Key Intermediates for the Asymmetric Synthesis of 3‐Indolyl Derivatives

Alkylideneindoleninium ions and alkylideneindolenines generated from 3‐substituted indoles are important intermediates in organic synthesis, which can be trapped by a large variety of nucleophilic reagents to construct biologically important 3‐indolyl derivatives. This Focus Review summarizes the recent developments in asymmetric syntheses of 3‐indolyl derivatives via alkylideneindoleninium ions or alkylideneindolenines. The elimination mechanism of leaving groups and asymmetric strategies are discussed.