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Notes and references
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Scheme 2 Trifluoromethylation of heterocyclic compounds.
¨
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complex III. Subsequently, III undergoes intramolecular trifluoro-
methylation to give radical intermediate IV. Then the oxidation of
IV by Cu(II) species (generated in situ) affords the precursor V of
product 3, returning Cu(I) species to the catalytic cycle. Apparently,
the undirected attack of CF3 to 1 would produce a mixture of o-, m-,
p-isomer of 3, but this process seems to be relatively slow in our
reaction. When a radical scavenger was added, the CF3 radical was
trapped and the reaction ceased (eqn (1)).
In summary, CuCl-catalyzed direct trifluoromethylation of
sp2 C–H bonds was realized, using the Togni reagent as the CF3
source. It is worth mentioning that this reaction achieves the
goal of converting C–H into C–CF3 with environmentally
friendly and readily available starting materials, which would
be of great benefit to the synthesis of trifluoromethyl com-
pounds. The utility of the pivalamido group holds the oppor-
tunities to introduce different functional groups onto the aryl
group or transform it into different functional groups through
known methods. Hence, the successful regio-selective trifluoro-
methylation of pivalamido arenes and hetero-arenes provides
new access to many synthetic therapeutic agents.
´
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A. Togni, Angew. Chem., Int. Ed., 2009, 48, 4332; (b) K. Niedermann,
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This work was supported by National Natural Science Foun-
dation of China (21102080, 20972085) and Tsinghua University
Initiative Scientific Research Program (2011Z02150).
c
4554 Chem. Commun., 2013, 49, 4552--4554
This journal is The Royal Society of Chemistry 2013