Electrochemistry-Enabled Ir-Catalyzed Vinylic C–H Functionalization

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.