Enantioselective Oxidative Phenol-Indole [3 + 2] Coupling Enabled by Biomimetic Mn(III)/Brønsted Acid Relay Catalysis

Abstract

A (salen)Mn(III) complex was used as a biomimetic surrogate of the metallocofactor of phenol-oxidizing enzymes, in combination with chiral phosphoric acid relay catalysis, enabling an enantioselective direct oxidative phenol-indole [3 + 2] coupling reaction to access structurally diverse chiral benzofuroindolines. Differing from previous methods that exclusively make use of isolatable quinones or their imines, this system is capable of harnessing transient N-Boc quinone imines, and highlights its synthetic potential with high enantioselectivities, high step and atom economy, benign reaction conditions, and remarkable catalytic turnover for chiral phosphoric acid (CPA) (low to 0.01 mol %; up to 4100 turnover number (TON)).