Origins of unique gold-catalysed chemo- and site-selective C–H functionalization of phenols with diazo compounds

Abstract

In past decade, gold revealed more and more unique properties in carbene chemistry. It was disclosed in our recent communication (<i>J. Am. Chem. Soc.</i> 2014, <b>136</b>, 6904) that gold carbenes have unprecedented chemo- and site-selectivity and ligand effect toward the functionalization of C-H bonds in phenols. In this full article, we report a comprehensively combined theoretical and experimental study on the mechanism of the insertion of gold carbenes into C-H and O-H bonds in phenol. It significantly revealed that the ligands have an important effect on C-H insertion and the reaction proceeds through a pathway involving the formation of an enolate-like intermediate. Moreover, two water molecules serving as a proton shuttle are believed to be the key issue for achieving chemoselective C-H functionalization, which is strongly supported by the DFT calculations and control experiments. It is the first time that a clear explanation is given about the prominent catalysis of gold carbenes toward C-H functionalization based on a theoretical and experimental study.