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.