Electrochemical
transition metal catalysis is a powerful strategy
for organic synthesis because it obviates the use of stoichiometric
chemical oxidants and reductants. C–H bond functionalization
offers a variety of useful conversions of simple and ubiquitous organic
molecules into diverse functional groups in a single synthetic operation.
This review summarizes recent progress in merging electrochemistry
with transition metal-catalyzed C–H functionalization, specifically
C–C, C–X (halogen), C–O, C–P, and C–N
bond formation.
Palladium-catalyzed C-H activation/C-O bond-forming reactions have emerged as attractive tools for organic synthesis. Typically, these reactions require strong chemical oxidants, which convert organopalladium(II) intermediates into the Pd or Pd oxidation state to promote otherwise challenging C-O reductive elimination. However, previously reported oxidants possess significant disadvantages, including poor atom economy, high cost, and the formation of undesired byproducts. To overcome these issues, we report an electrochemical strategy that takes advantage of anodic oxidation of Pd to induce selective C-O reductive elimination with a variety of oxyanion coupling partners.
Electrochemical oxidation represents an environmentally friendly solution to conventional methods that require caustic stoichiometric chemical oxidants. However, C-H functionalizations merging transition-metal catalysis and electrochemical techniques are, to date, largely confined to the use of precious metals and divided cells. Herein, we report the first examples of copper-catalyzed electrochemical C-H aminations of arenes at room temperature using undivided electrochemical cells, thereby providing a practical solution for the construction of arylamines. The use of n-BuNI as a redox mediator is crucial for this transformation. On the basis of mechanistic studies including kinetic profiles, isotope effects, cyclic voltammetric analyses, and radical inhibition experiments, the reaction appears to proceed via a single-electron-transfer (SET) process, and a high valent Cu(III) species is likely involved. These findings provide a new avenue for transition-metal-catalyzed electrochemical C-H functionalization reactions using redox mediators.
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