We present a new paradigm for nitroxyl-mediated processes via the merger of oxoammonium cation-mediated oxidation with visible-light photoredox catalysis. The integration of these two forms of catalysis has been realised for the oxidative amidation of aldehydes, furnishing N-acylated heterocycles. Extension of this process to the oxidative amidation of alcohols via the intermediacy of an aldehyde was successfully pursued, thus proffering a general oxidation platform. The activated amides synthesised here are excellent synthetic handles for acylation.
A methodology
is reported for preparing amides using amines as
an acyl source. The protocol involves the visible-light-promoted oxidative
amidation of amines with pyrazole to synthesize N-acyl pyrazoles followed by transamidation. By combining photoredox
catalysis with oxoammonium cations in the presence of sodium persulfate
as a terminal oxidant, the N-acyl pyrazoles could
be prepared efficiently and effectively using blue LEDs. The transamidation
step was performed without the need to purify the N-acyl pyrazole intermediate, and a range of amides were generated
in good to excellent yields.
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