An acid-promoted novel skeletal rearrangement initiated by intramolecular ipso-Friedel-Crafts-type addition to 3-alkylidene indolenium cations

摘要

An acid-promoted novel skeletal rearrangement is described. Using trifluoroacetic acid as the acid promoter, an intramolecular ipso-Friedel-Crafts-type addition of phenols to 3-alkylidene indolenium cations, formation of iminium cations through rcaromatization of the spirocyclohexadienone units, and intramolecular Pictet-Spengler reaction proceeded sequentially, producing tricyclic indole derivatives.