Electrochemical synthesis has been
rapidly developed over the past
few years, while a vast majority of the reactions proceed through
a radical pathway. Understanding the properties of radical intermediates
is crucial in the mechanistic study of electrochemical transformations
and will be beneficial for developing new reactions. Nevertheless,
it is rather difficult to determine the “live” radical
intermediates due to their high reactivity. In this work, the formation
and structure of sulfonamide N-centered radicals
have been researched directly by using the time-resolved electron
paramagnetic resonance (EPR) technique under electrochemical conditions.
Supported by the EPR results, the reactivity of N-centered radicals as a mediator in the hydrogen atom transfer (HAT)
approach has been discussed. Subsequently, these mechanistic study
results have been successfully utilized in the discovery of an unactivated
C(sp3)–H arylation reaction. The kinetic experiments
have revealed the rate-determined step is the anodic oxidation of
sulfonamides.
We formed C(sp3)–C(sp2) bonds under electrochemical conditions by using NHP esters and N-heteroarenes without any catalysts. Our approach could be a complement to the Kolbe reaction and a promising strategy for finding more new reactions.
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