Synthesis of novel chiral phosphoric acid-bearing two acidic phenolic hydroxyl groups and its catalytic evaluation for enantioselective Friedel-Crafts alkylation of indoles and enones

Abstract

A novel chiral phosphoric acid catalyst bearing two acidic phenolic hydroxyl groups was synthesized. Its catalytic activity as a chiral Brøsted acid has been examined in the enantioselective Friedel-Crafts alkylation of indoles and enones as a model reaction. In comparison with the other chiral phosphoric acid catalysts, the reaction catalyzed by the novel chiral catalyst afforded the desired 3-substituted indoles in a higher enantioselectivity (up to 69% ee).