3
Scheme 3. Investigation of substrates scope [a], [b]
give the desired product 3b and HI. Finally, treatment of t-BuO·
radical with HI led to the catalyst I2 which can realized the reaction
cycle.
Scheme 5. Plausible mechanism of 1b with 2a.
[a]
In conclusion, we have described an oxidative coupling of
electron-rich arenes with thiols to give thioethers in good to excellent
yields. The reaction was proposed to go through an electrophilic
aromatic substitution path way. Most attractively, the reaction made
direct use of simple and abundant starting materials without
requiring transition metal catalysts, thus facilitating operation on the
benchtop. Therefore, the protocol will open a new avenue for the C-S
bond-forming reactions and should find broad application in
synthetic chemistry.
Reaction conditions: under nitrogen atmosphere, thiols (0.5 mmol),
aromatic substrates (1.0 mmol), I2 (0.1 mmol), DTBP (2.5 mmol), 120 oC,
24h.
[b] Isolated yield.
To further explore the mechanism of this reaction, several control
experiments were carried out as shown in Scheme 4. Treatment of 4-
methylbenzenethiol (1b) only under the standard conditions, 1,2-dip-
tolyldisulfane (4) was obtained in 97% yield (eq 1). Furthermore, the
reaction of 4 with 2a gave te desired 3b in 88% yield (eq 2). Besides
that, the radical scavenger TEMPO (2,2,6,6-tetramethyl-1-
piperidinyloxy) completely inhibited the 3b formation (eq 3). This
result indicated that the present transformation might involve a
radical process. However, treatment of 1,2-dip-tolyldisulfane (4)
with 2a under 0.25 mmol of I2 afforded the desired product 3b in
84% yields (eq 4).
Acknowledgments
The authors gratefully acknowledge the financial support from
the National Natural Science Foundation of China (Nos.
21302110, 21302109 and 21375075), the Project of Shandong
Province Higher Educational Science and Technology Program
(J13LD14), the Taishan Scholar Foundation of Shandong
Province, and the Natural Science Foundation of Shandong
Province (ZR2013BQ017). We thank Xiao Zhu in this group for
reproducing the results of 3a and 3p.
References and notes
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Scheme 4. Control experiments
Based on the preliminary results above and the previous report, a
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transformed to 1,2-dip-tolyldisulfane (4) under the present reaction
conditions. Next, 1,2-dip-tolyldisulfane (4) reacted with I2 to provide
an electrophilic species p-MePhSI (5),9 which attacked 1,3,5-
trimethoxybenzene (2a) to yield 6, which underwent aromatization to
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Hu, M.; Cheng,J. J. Org. Chem. 2010, 75, 6732−6735; (e) Ranjit, S.; Lee,