The
reductive opening of epoxides represents an attractive method
for the synthesis of alcohols, but its potential application is limited
by the use of stoichiometric amounts of metal hydride reducing agents
(e.g., LiAlH4). For this reason, the corresponding homogeneous
catalytic version with H2 is receiving increasing attention.
However, investigation of this alternative has just begun, and several
issues are still present, such as the use of noble metals/expensive
ligands, high catalytic loading, and poor regioselectivity. Herein,
we describe the use of a cheap and easy-to-handle (cyclopentadienone)iron
complex (1a), previously developed by some of us, as
a precatalyst for the reductive opening of epoxides with H2. While aryl epoxides smoothly reacted to afford linear alcohols,
aliphatic epoxides turned out to be particularly challenging, requiring
the presence of a Lewis acid cocatalyst. Remarkably, we found that
it is possible to steer the regioselectivity with a careful choice
of Lewis acid. A series of deuterium labeling and computational studies
were run to investigate the reaction mechanism, which seems to involve
more than a single pathway.
Herein we report a study on the use of donor‐acceptor cyanoarenes as photocatalysts for C−O and C−N coupling reactions promoted by nickel. We found that some of these stable and readily available organic compounds can replace the precious metal photocatalysts originally employed in these methodologies. After reaction optimization, the application scope of the best performing dyes was investigated and found to cover several nucleophiles (alcohols and amines) and aryl bromides. Control experiments, fluorescence quenching studies and examination of yield trends suggest that both etherification and amination probably proceed via a dark NiI/NiIII‐catalytic cycle initiated and sustained by a photoredox cycle involving the organic photocatalysts.
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