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maximum absorption peaks of diphenyl disulfide solutions were
observed around 350 nm. As we also found in the other reactions
of diphenyl disulfide, the irradiation with the light of 450 nm
provided the best yields18. We speculated that the energy
provided by the light of 450 nm is appropriate for the break of
the S-S bond. The light of shorter wavelengths provides too
much energy to cause the side reactions. On the other hand, the
light of longer wavelengths cannot provide the enough energy to
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A tentative reaction mechanism is outlined in Scheme 3. The
diphenyl disulfide is firstly activated under the photoirradiation.
A single electron transfer from iodide to the activated diphenyl
disulfide provides a diphenyl disulfide anion radical A. The
fragmentation of A generates a thiophenol anion and a
phenylthiyl radical B. The coupling of iodine radical and B gives
arylsulfenyl iodine C. The subsequent electrophilic substitution
with the indole affords the 3-arylthioindole product12.
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Scheme 3. Proposed reaction mechanism.
In summary, we have developed a visible-light promoted
synthesis of 3-arylthioindoles from indoles and diaryl disulfides.
The reaction can be promoted by the catalytic amount of sodium
iodide. A series of 3-arylthioindoles were prepared in good yields.
The reaction is suggested to occur via electrophilic arylsulfenyl
iodine intermediates, which are formed after the photo promoted
single electron transfer from iodide to diphenyl disulfides. The
finding provides a practical strategy for the synthesis of 3-
arylthioindoles.
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Acknowledgments
We thank the National Natural Science Foundation of China (no.
21472248) for the financial support of this study.
Supplementary Material
Supplementary data associated with this article can be found in
1
procedure, characterization data of products, UV-vis spectra, H
and 13C NMR spectra.
References and notes
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