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ChemComm
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DOI: 10.1039/C5CC09179A
COMMUNICATION
Journal Name
To figure out whether the in situ generated aryl
This work was financially supported by the National Natural
.
difluoroemthylene radical (ArCF2 ) would be involved in the Science Foundation of China (21172141, 21302121, 21572128)
reaction, we conducted the inhibition experiment of 1a with and the Science Foundation of Shanghai Municipal
the addition of the known radical scavenger of TEMPO Commission of Sciences and Technology (15230724800). We
(2,2,6,6-tetramethyl-1-piperidinyloxy), 1, 4-dinitrobenzene or thank the Laboratory of Micro-structures of Shanghai
hydroquinone under the standard reaction condition (see ESI). University for structural analysis.
Significant suppression of the formation of the desired product
.
3aa suggested that a ArCF2 radical species would act as an
Notes and references
important role in the current reaction condition.
To obtain some information on the reaction pathway, we
also investigated the control experiments and revealed that
the reaction still gave 12% yield even without Ag(I) catalyst
(see ESI). No reaction occurred in the absence of an oxidant.
1
2
3
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.
The possible formation of ArCF2 radical species generated
independently from AgNO3 was ruled out. The control
experiments authenticated the importance of the combination
of both of AgNO3 and (NH4)2S2O8.
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On the basis of these results and previous reports,7a, 11
a
postulated mechanism is depicted in Scheme 2. We believe
that in this work, Ag(I) is initially oxidized by the persulfate
((NH4)2S2O8) to generate the Ag(II) cation in situ, which could
obtain a single electron from difluoroacetate to produce the
carboxyl radical. Quick decarboxylation of the carboxyl radical
with the loss of CO2 provides the corresponding gem-
Front. 2014, 1, 113; (d) G. B. Ma, W. Wan, Q. Y. Hu, H. Zh.
Jiang, J. Wang, Sh. Zh. Zhu, J. Hao, Chem. Commun. 2014, 50
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,
difluoromethylene radical
addition to isonitrile functionality to form the imidoyl radical
Subsequent intramolecular attack of the imidoyl radical on the
pendant aromatic ring generates cyclohexadienyl-type
radical , which gets oxidized by sulphate radical anion
through a single electron transfer (SET) process to afford the
cyclohexadienyl cation D. Finally, aromatiztion of through
deprotonation leads to the desired gem-difluoromethylenated
phenanthridine
A, which undergoes intermolecular
B.
a
4
5
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4
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In summary, we have demonstrated the simple and practical
protocol for the generation of aryl difluoroemthylene radicals
through the Ag(I)-catalyzed oxidative decarboxylation of aryl
difluoroacetates. This transition-metal-catalyzed oxidative
decarboxylative gem-difluoromethylenation might reasonably
be expected to become a novel and convenient synthetic
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,
,
strategy
for
constructing
gem-difluoromethylenated
phenanthridine, due to the stability, easy availability of
difluoroacteates and catalyst, the mild experimental
conditions and the wide functional group compatibility.
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4 | J. Name., 2012, 00, 1-3
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