Organic Letters
Letter
Scheme 3. Mechanistic Investigation
ASSOCIATED CONTENT
* Supporting Information
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S
The Supporting Information is available free of charge on the
Details of experiment procedures, control experiments,
and full spectroscopic data for all new compounds
trifluoromethoxylated product was formed, and the aryl-
TEMPO adduct (51) was isolated in 64% yield. To further
investigate whether aryl radical species are generated in the
current trifluoromethoxylation process, a radical clock probe
was introduced by using 2-(allyloxy)aryl diazonium (52) as a
substrate in this transformation.15a,b The regular trifluoro-
methoxylation product (53) was formed in 15% yield (19F
NMR), whereas no cyclized product (54) could be detected.
The low yield of trifluoromethoxylation product (53) is due to
the neighboring and electron-donating effects of allyloxy group,
as we have observed during substrate scope studies. Moreover,
during our reactions, we observed that most silver remained as
Ag(I) salt rather than as Ag(0).
AUTHOR INFORMATION
Corresponding Authors
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ORCID
Author Contributions
§Y.-M.Y. and J.-F.Y. contributed equally to this work.
Notes
The authors declare no competing financial interest.
For Sandmeyer-type transformations, the majority of the
reactions take place by the SRN1(Ar) (radical nucleophilic
aromatic substitution) mechanism in which an initial electron
transfer from Cu(I) takes place, allowing for the formation of
an aryl radical.20 Tang proposed a photocatalyzed aryl radical
formation, addition to CuII(OCF3)2, and reductive elimination
to form an aryl−OCF3 bond mechanism.13 Given the facts of
our AgOCF3-mediated trifluoromethoxylation of diazonium,
(1) one equivalent of Cu(I) salt hindered the transformation,
and no desired aryl trifluoromethyl ether product formed (see
substrates with an electron-withdrawing group at the meta
position gave the best yields, we proposed a silver-involved
ACKNOWLEDGMENTS
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Financial support was provided by the National Natural
Science Foundation of China 21302231, Hunan Provincial
Natural Science Foundation of China 14JJ3021, and Ph.D.
Programs Foundation of Ministry of Education of China
20130162120032. We thank Valuable and Precision Instru-
ments of Central South University for NMR assistance. We
thank Central South University High Resolution Mass
Spectrometry Laboratory of Advanced Research Center and
the Sun Yat-sen University Mass Spectrometry Facilities for
HRMS−ESI assistance.
REFERENCES
SRN1(Ar) mechanism (Scheme 4). A single electron transfer
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Scheme 4. Proposed Mechanism
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(SET) from AgIOCF3 formed an aryl radical, and the
sequential OCF3 group transfer from Ag(II) formed a final
aryl−OCF3 bond. An alternative mechanism might be the
oxidative addition−reductive elimination involving high-valent
silver species, as Wang has demonstrated in the AgCF3-
mediated trifluoromethylation of aryldiazonium salts.15c
However, the unambiguous mechanism of this silver-mediated
trifluoromethoxylation of aryl diazonium needs more rigorous
investigation.
In summary, we have developed a silver-mediated
Sandmeyer-type trifluoromethoxylation of aryl/heteroaryl
diazonium tetrafluoroborates with AgOCF3 as the trifluor-
omethoxylating reagent and TFMT as the precursor. The
reaction tolerates a range of functional groups and is applicable
to heteroarenes such as pyridines and late-stage trifluorome-
thoxylation reactions of complex small molecules. Further
efforts toward combining the diazotization and the Sandmeyer
reaction into a one-pot procedure and toward reducing the
cost of trifluoromethoxylation reaction are underway.
́
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