Oxoammonium-Catalyzed Ether Oxidation via Hydride Abstraction: Methodology Development and Mechanistic Investigation using Paramagnetic Relaxation Enhancement NMR

Hydride abstraction represents a promising yet underexplored approach in the functionalization of C–H bonds. In this work, we report the oxidation of α-C–H bonds of ethers via oxoammonium catalysis using 3-chloroperbenzoic acid (mCPBA) as the terminal chemical oxidant or by means of electrochemistry. Mechanistic studies revealed intricate equilibria and interconversion events between various catalytic intermediates in the presence of mCPBA, which alone however was incompetent to drive catalytic turnover. The addition of a small amount of strong acid HNTf2 or weakly coordinating salt NaSbF6 turned on catalytic turnover and promoted ether oxidation with excellent efficiency. NMR experiments leveraging paramagnetic relaxation enhancement effect allowed for quantification of open-shell catalytic intermediates in real time during the reaction course, which aided the identification of catalyst resting states and elucidation of reaction mechanisms.