A scalable
enantioselective nickel-catalyzed electrochemical
reductive homocoupling of aryl bromides has been developed, affording
enantioenriched axially chiral biaryls in good yield under mild
conditions using electricity as a reductant in an undivided cell.
Common metal reductants such as Mn or Zn powder resulted in significantly
lower yields in the absence of electric current under otherwise identical
conditions, underscoring the enhanced reactivity provided by the combination
of transition metal catalysis and electrochemistry.
Transition‐metal‐catalyzed coupling reactions are useful tools for synthesizing aryl sulfur compounds. However, conventional transition‐metal‐catalyzed thiolation of aryl bromides and chlorides typically requires the use of strong base under elevated reaction temperature. Herein, we report the first examples of nickel‐catalyzed electrochemical thiolation of aryl bromides and chlorides in the absence of an external base at room temperature using undivided electrochemical cells.
A highly regioselective Ni‐catalyzed electrochemical reductive relay cross‐coupling between an aryl halide and an alkyl halide has been developed in an undivided cell. Various functional groups are tolerated under these mild reaction conditions, which provides an alternative approach for the synthesis of 1,1‐diarylalkanes.
Synergistic use of electrochemistry and organometallic
catalysis
has emerged as a powerful tool for site-selective C–H functionalization,
yet this type of transformation has thus far mainly been limited to
arene C–H functionalization. Herein, we report the development
of electrochemical vinylic C–H functionalization of acrylic
acids with alkynes. In this reaction an iridium catalyst enables C–H/O–H
functionalization for alkyne annulation, affording α-pyrones
with good to excellent yields in an undivided cell. Preliminary mechanistic
studies show that anodic oxidation is crucial for releasing the product
and regeneration of an Ir(III) intermediate from a diene-Ir(I) complex,
which is a coordinatively saturated, 18-electron complex. Importantly,
common chemical oxidants such as Ag(I) or Cu(II) did not give significant
amounts of the desired product in the absence of electrical current
under otherwise identical conditions.
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