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ChemComm
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groups were appropriate for this reaction, affording the target
products in excellent yields (Table 3, 2n-p). However, no product
was obtained when the substrate with an electron-withdrawing
group or with a free N-H acryl amide was employed (Table 3, 2q
and 2r). It should be noted that cyclization of crotonyl derivatives
(Table 3, 2s-2t) gave exclusively indolin-2-ones in good yields
again with no trace of cyclization onto the allyl double, which is
in consistent with the results reported by Jones et al.15
DOI: 10.1039/C5CC00072F
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10
On the basis of the above experiments and related reports,10
a plausible mechanism for the reaction was shown in Scheme 2.
Excitation of the metal catalyst under visible light afforded the
excited IrIII* species, which oxidizes Et3N to give the reduced
species IrII, along with the radical cation of the amine. The
55
60
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15 electron-rich metal complex IrII then reduces the aryl iodide 1a to
afford the key radical intermediate A and regenerates the
photocatalyst IrIII. The intramolecular radical addition of
intermediate A to the ɑ, β-unsaturated amide forms radical B,
which can be rapidly reduced by a hydrogen-atom abstraction
20 from the ɑ-amino position of the iminium radical cation to give
the indolin-2-one.16
65
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R
N
R
N
70
O
[Ir(ppy)2(dtb-bpy)] PF6
O
I
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1b
1a
H
Ir(II)
NEt3
75
visible light
80
NEt2
*Ir(III)
NEt3
Ir(III)
R
R
N
N
O
O
5-exo-trig
85
B
A
Scheme 2. Proposed mechanism
90
In conclusion, we have developed an efficient visible light
25 induced [Ir(ppy)(dtb-bpy)PF6]-catalyzed reductive cyclization
reaction of o-iodophenylacrylamides via a 5-exo-trig radical
cyclization under mild reaction conditions, affording the
biologically important indolin-2-ones in moderate to good yields.
Further study towards expanding the application of photoredox
30 catalysis in other reaction is currently underway in our laboratory.
95
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This work was financially supported by National Natural Science
Foundation of China. We thank the Instrumental Analysis Center
of Shanghai Jiao Tong University for microanalysis.
100
105
110
Notes and references
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