4
Tetrahedron
iodonium using Cu(OAc)2 as oxidant. The reaction tolerates
(a) Transmetallation from I(III) to Pd(II) followed by C-H
activation (Electron Rich iodonium salts)
several functional groups on both the moieties. The methodology
can be used either for late stage arylations of the quinoline
moiety or further modifications on the phenyl ring for
applications in medicinal chemistry.
Cu(0)
Ph I+
-
Ar
Pd(II)
BF4
Cu(II)
Acknowledgments
Pd oxidation
Transmetallation
SY thanks SERB, India for funding this work. DC
(09/085/0119/2016-EMR-I) and AP (09/085/0118/2016-EMR-I)
thank Council of Scientific and Industrial Research (CSIR), India
for Senior Research Fellowships.
Pd
Pd(0)
Ar
Transmetallation
via
C-H Activation
Reductive
elimination
References and notes
Pd
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N
(b) C-H activation by Pd(II) Transmetallation to Pd(IV)
(Electron deficient iodonium salts)
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Scheme 4. Probable mechanism of the arylation of
the quinolines.
lower reactivity of the electron deficient aryls towards the
oxidative addition to the Pd(0) species, initially the insertion of
the quinoline moiety occurs through C-H activation followed by
oxidative addition of the aryliodonium salt to generate Pd(IV)
intermediate and consequent reductive elimination to generate the
product 3.28
The recyclability of the solid PdNC was then verified by the
reaction of 1a with 2a. The catalyst was recovered by means of
centrifugation of the reaction mixture after dilution with water
and ethyl acetate and reused as the catalyst for successive
reactions for up to 8 cycles (Figure S8, SI). The yields of the
reactions dropped very insignificantly up to the 5th cycle and
quite rapidly in the subsequent cycles. As a preliminary test to
determine whether the actual catalyst was the nanocatalyst or a
leached Pd species, the in situ ICPMS analysis of the reaction
medium (for the reaction between 1a and 2a) was also carried out
to detect any leached Pd species after removal of the catalyst. A
very negligible level of Pd (3.3891 ppb) was detected that
indicated that probably the reaction was catalyzed by the PdNC
nanoparticles itself.
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Lai, H. W.; Wang, D. Appl. Organometal. Chem. 2018, 32, 3970;
c) Shang, Y. Appl. Organometal. Chem. 2018, 32, 4484.
In conclusion, we have established a new approach towards
the direct synthesis of 3-arylquinolines through the nano Pd
catalyzed C-H arylation reaction of quinolines and diaryl