A novel direct catalytic asymmetric synthesis of cyclic indole derivatives by intramolecular carbopalladation of allenes and subsequent intramolecular amination

Abstract

A novel asymmetric synthetic method allowing a facile entry to chiral cyclic indole compounds has been developed by means of asymmetric carbopalladation–amination of allenes using a palladium catalyst with chiral phosphine ligands: intramolecular carbopalladation of allenes, which bear o-iodophenyl amino groups, was followed by intramolecular amination of the resultant π-allylpalladium intermediates. The enantioselectivity of the asymmetric reactions were found to be dependant on the chiral phosphine ligands and the solvent used; N-methylpyridone was the most effective solvent for achieving efficient enantioselectivity with high chemical yields, and ( S)-(−)-BINAP or ( S)-Tol-BINAP were revealed to be the most useful of the chiral phosphine ligands examined, depending on the substrate employed.