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COMMUNICATION
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triplet Ru+2* which then reacts with aryldiazonium salt to form
Ru+3 and aryl radical. In the other catalytic cycle, palladium (II)
coordinates with phenylurea followed by C-H activation to
form palladacycle intermediate, (P). Later, the aryl radical
generated from the photoredox cycle reacts with palladacycle,
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(P) to from Pd(III) intermediate, (Q)
.
Finally, Ru+2 is
regenerated from Ru+3 by gaining one electron from the Pd (III)
intermediate,(Q) to form Pd (IV) intermediate, (R), to complete
the photoredox cycle. The Pd (IV) intermediate, (R) finally
undergoes reductive elimination to form C-H arylated product,
3aa and Pd(II), which again can participitate in the C-H
activation step (Figure 2). On the other hand NH arylation of
phenylureas usually involves a Pd(0)/Pd(II) catalytic cycle or a
Ullmann type coupling with Cu catalysts.
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Figure 2: Proposed mechanism for the dual catalytic cycle.
S.-J. Lou, Y.-J. Mao, D.-Q. Xu, J.-Q. He, Q. Chen and Z.-Y. Xu,
In conclusion we have developed an efficient route for the
chemoselective C-H arylation of phenylureas using a dual
palladium-photoredox catalysis. The reaction proceeds
smoothly with catalyst loading as low as 0.33 mol% of
Ru(bpy)3Cl2 & 1.7 mol% & Pd(OAc)2 respectively without
external oxidant & additive free conditions. We have also
shown regioselective C-H arylation of N,N’-diaryl substituted
phenylureas by carefully chosing the aryl substitutents. Broad
substrate scope, high functional group tolerance, good regio-
& chemo-selectivity make this process an appealing strategy.
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Acknowledgements
K. Sahoo, S. P. Midya, V. G. Landge and E. Balaraman, Green
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This work is supported by the SERB, India. P.G. thanks
DST-SERB for a Ramanujan fellowship (SB/S2/RJN-
041/2017), & IISER Tirupati.
Neufeldt and M. S. Sanford, J. Am. Chem. Soc., 2011, 133
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18566-18569.
Conflicts of interest
“There are no conflicts to declare”.
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Notes and references
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