Silver-mediated radical aryltrifluoromethylthiolation of activated alkenes by S-trifluoromethyl 4-methylbenzenesulfonothioate

Article abstract of DOI:10.1016/j.tetlet.2018.03.058

Herein, we describe the preparation of trifluoromethylthiol-substituted oxindoles by silver-mediated aryltrifluoromethylthiolation of activated alkenes, using S-trifluoromethyl 4-methylbenzenesulfonothioate as a F₃CS radical source and showing that the reagent availability, mild conditions, and broad functional group compatibility of this transformation make it a viable alternative strategy of constructing C_sp3–SCF₃ bonds.

Full text of DOI:10.1016/j.tetlet.2018.03.058

Accepted Manuscript
Silver-Mediated Radical Aryltrifluoromethylthiolation of Activated Alkenes by
S-Trifluoromethyl 4-Methylbenzenesulfonothioate
Xia Zhao, Bo Yang, Aoqi Wei, Jianqiao Sheng, Miaomiao Tian, Quan Li, Kui
Lu
PII:
S0040-4039(18)30372-1
https://doi.org/10.1016/j.tetlet.2018.03.058
TETL 49827
DOI:
Reference:
Tetrahedron Letters
To appear in:
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Revised Date:
Accepted Date:
25 January 2018
20 March 2018
20 March 2018
Please cite this article as: Zhao, X., Yang, B., Wei, A., Sheng, J., Tian, M., Li, Q., Lu, K., Silver-Mediated Radical
Aryltrifluoromethylthiolation of Activated Alkenes by S-Trifluoromethyl 4-Methylbenzenesulfonothioate,
Tetrahedron Letters (2018), doi: https://doi.org/10.1016/j.tetlet.2018.03.058
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Graphical Abstract
Silver-Mediated Radical
Leave this area blank for abstract info.
Aryltrifluoromethylthiolation of Activated
Alkenes by S-Trifluoromethyl 4-
Methylbenzenesulfonothioate
Xia Zhao,* Bo Yang, Aoqi Wei, Jianqiao Sheng, Miaomiao Tian, Quan Li and Kui Lu

1
Tetrahedron Letters
Silver-Mediated Radical Aryltrifluoromethylthiolation of Activated Alkenes by S-
Trifluoromethyl 4-Methylbenzenesulfonothioate
Xia Zhaoa, , Bo Yanga,c, Aoqi Weia,c, Jianqiao Shenga, Miaomiao Tiana, Quan Lib and Kui Lub
a College of Chemistry, Tianjin Key Laboratory of Structure and Performance for Functional Molecules, Key laboratory of Inorganic-organic Hybrid Functional
Material Chemistry, Ministry of Education, Tianjin Normal University, Tianjin 300387, China
b College of Biotechnology, Tianjin University of Science & Technology, Tianjin 300457, China
c These two authors contributed equally to this work
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
Herein, we describe the preparation of trifluoromethylthiol-substituted oxindoles by silver-
mediated aryltrifluoromethylthiolation of activated alkenes, using S-trifluoromethyl 4-
methylbenzenesulfonothioate as a F3CS radical source and showing that the reagent availability,
mild conditions, and broad functional group compatibility of this transformation make it a viable
alternative strategy of constructing Csp3–SCF3 bonds.
Available online
Keywords:
Silver-Mediated
Radical
2009 Elsevier Ltd. All rights reserved.
Aryltrifluoromethylthiolation
Activated Alkenes
Oxindole
1. Introduction
driven radical trifluoromethylthiolation of alkenes by N-
trifluoromethylthiosaccharin (2) (Shen's reagent) (Scheme 1, Eq.
3).11 However, the preparation of compounds 1 and 2 requires the
use of expensive AgSCF3 or CuSCF3. In 2016, Shen et al.
Trifluoromethylthiolation has recently emerged as a hot
organic/medicinal chemistry research field.1 Since the
trifluoromethylthiol (CF3S) group is highly lipophilic (Hansch
parameter πR = 1.44)2 and electron-withdrawing, its incorporation
into bioactive molecules can improve their cell membrane
permeation ability3 and metabolic stability,4 which makes the
development of mild and efficient trifluoromethylthiolation
methods a task of high significance.
reported
an
elegant
radical-mediated
phenylsulfonyl-
difluoromethylthio-1,2-difunctionalisation of alkenes by S-
difluoromethyl benzenesulfonothioate (3).12 Recently, Xu et al.
reported a gold and visible-light mediated
In addition to nucleophilic trifluoromethylthiolation employing
−
AgSCF3,5 CuSCF3,6 or Me4NSCF37 as SCF3 sources, great
progress has been made in the field of electrophilic
trifluoromethylthiolation, with a series of easy-to-handle and
shelf-stable trifluoromethylthiolation reagents currently being
available.8 However, although a number of aromatic molecules
have
been
trifluoromethylthiolated
reagents,
by
the
above
radical
nucleophilic/electrophilic
the
trifluoromethylthiolation of alkenes remains underexplored,
mainly due to the limited number of reliable methods of
generating the F3CS radical. The most common F3CS radical
source, used in many impressive transformations, is AgSCF3,
which, however, is expensive and requires in situ oxidation by a
strong oxidant to generate the SCF3 radical (Scheme 1, Eq. 1).9 In
2016, Hopkinson et al. reported visible-light-promoted radical
trifluoromethylthiolation
of
styrenes
by
2-
((trifluoromethyl)thio)isoindoline-1,3-dione (1) (Scheme 1, Eq.
Scheme 1 Radical aryltrifluoromethylthiolation of activated alkenes.
2).10 Recently, Dagousset and Magnier reported visible-light-
———
 Xia Zhao. Tel.: +86 22 23766531; fax: +86 2223766531; e-mail: hxxyzhx@mail.tjnu.edu.cn

2
Tetrahedron Letters
phenylsulfonyl-trifluoromethylthio-1,2-difunctionalisation of
17
18
19
1.8
1.8
1.8
AgF/1.8
AgF/1.8
AgF/1.8
K2S2O8/3.6
K2S2O8/3.6
K2S2O8/3.6
20
20
20
Toluene
NMP
0
0
alkenes by S-trifluoromethyl 4-methylbenzenesulfonothioate
(4).13 Due to being interested in the development of efficient C–S
bond construction methods,14 we herein utilised compound 4,
easily prepared from trimethyl(trifluoromethyl)silane (5), N,N-
diethyl-1,1,1-trifluoro-l4-sulfanamine (6), aniline (7), and sodium
DMF
34
aReaction conditions: 9a (0.25 mmol), 4 (0.3–0.5 mmol), Ag(I) salt (0.3–0.5
mmol), and oxidant (0.9 mmol)) in solvent (3 mL) for 5 h at the indicated
temperature. bYield of isolated product after silica gel chromatography.
cHMPA (0.125 mmol) was used as an additive. dDMSO (2 mL) was used.
eDMSO (4 mL) was used.
4-methylbenzenesulfinate (8) in two steps,8a, as an alternative
15
F3CS radical source, successfully achieving silver-mediated
oxidative aryltrifluoromethylthiolation of activated alkenes to
produce trifluoromethylthiol-substituted oxindoles (Scheme 1, Eq.
4).
With the optimised reaction conditions in hand, the scope of
activated alkenes was investigated, with the results presented in
Scheme 2. N-methyl-N-phenylmethacryl amides
9 with both
2. Results and discussion
electron-donating and electron-withdrawing substituents in ortho-,
meta-, and para-positions of the aniline ring (9b–9l) were smoothly
converted into the corresponding oxindoles. Notably, when N-
methyl-N-(pyridin-2-yl)methacrylamide (9m) and N-methyl-N-
(naphthalen-1-yl)methacrylamide (9n) were employed as substrates,
the desired products 10m and 10n were obtained in relatively low
yields. Then, other N-substitutes-N-phenylmethacryl amides (9o–9s)
were tested, affording the desired aryltrifluoromethylthiolation
products in moderate yields except for 9r, which was transformed
into 10r in 34% yield. Finally, α-substituted acrylamides (9t–9w)
were examined, and it was found that ethyl, benzyl, and
methoxymethyl substituents were tolerated, and the desired products
(10t–10w) were obtained in moderate to good yields.16
Treatment of N-methyl-N-phenylmethacrylamide (9a) with 4
in
the
presence
of
AgNO3,
(HMPA)
K2S2O8,
in
and
dimethyl
hexamethylphosphoramide
sulfoxide (DMSO) at 40 °C afforded the desired
aryltrifluoromethylthiolation product 10a (24% yield, Table 1,
entry 1) and the non-desired arylsulfoxidation product 11a (40%
yield). When the reaction was carried out without HMPA, the
yield of 10a increased to 38%, with only trace amount of 11a
detected (Table 1, entry 2). To optimise the reaction conditions,
various oxidants (Na2S2O8, (NH4)2S2O8, t-BuOOH, and (t-BuO)2
(Table 1, entries 3–6)) were investigated, but none of them was
superior to K2S2O8, with subsequent screening of silver salts
(AgSbF6, AgOTf, and AgF) showing that AgF afforded the best
yield (Table 1, entries 7–9). Finally, the loading of 4 and AgF,
reaction temperature, reactant concentration, and solvent were
examined. When the loadings of 4 and AgF were increased from
1.2 to 1.8 equivalents, the yield of 10a increased from 42 to 58%
(Table 1, entries 10 and 11). However, a further loading increase
to 2.0 equivalents was counterproductive (Table 1, entry 12).
Decreasing the reaction temperature to 20 °C improved the yield
to 71% (Table 1, entry 13), whereas increasing the concentration
of 9a from 0.083 to 0.125 M or decreasing it from 0.083 to 0.063
M diminished the yield (Table 1, entries 14 and 15). When other
solvents such as acetonitrile (CH3CN), toluene, and 1-
methylpyrrolidin-2-one (NMP) were used, no desired product
was obtained, except for DMF, in which case 10a was isolated in
34% yield (Table 1, entries 16–19). Thus, the optimised reaction
conditions for the aryltrifluoromethylthiolation of 9a were as
follows: 9a (0.25 mmol), 4 (0.45 mmol), AgF (0.45 mmol),
K2S2O8 (0.9 mmol), and DMSO (3 mL) at 20 °C.
Table 1. Optimisation of aryltrifluoromethylthiolation of 9a by 4
in the presence of diverse silver salts and oxidants.a
Yield
Temperature
Entry 4/equiv. Ag(I)/equiv. Oxidant/equiv.
Solvent of 10a
(C)
(%)b
24c
1
2
1.2
1.2
1.2
1.2
1.2
1.2
AgNO3/1.2 K2S2O8/3.6
AgNO3/1.2 K2S2O8/3.6
AgNO3/1.2 Na2S2O8/3.6
AgNO3/1.2 (NH4)2S2O8/3.6
AgNO3/1.2 t-BuOOH/3.6
AgNO3/1.2 (t-BuO)2/3.6
40
40
40
40
40
40
40
40
40
40
40
40
20
20
20
20
DMSO
DMSO
38
3
DMSO trace
4
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
CH3CN
29
0
5
Scheme 2. Substrate scope of activated alkene aryltrifluoromethylthiolation.
6
0
7
1.2 AgSbF6/1.2 K2S2O8/3.6
40
40
42
55
58
52
71
58d
65e
0
To understand the mechanism of the above transformation, a
series of experiments were carried out. In the absence of K2S2O8
or in the presence of 1.8 equivalents of TEMPO as a radical
scavenger, no desired product was detected (Scheme 3, Eqs. 1
and 2, respectively), which supported the hypothesis that the
reaction proceeded via a radical pathway. To gain further
insights, 4 was treated with AgF in the presence of K2S2O8 in
DMSO at 20 °C, and the reaction was monitored by 19F-NMR for
3 h, with peaks of 1,2-bis(trifluoromethyl)disulfane (11) (δ = –
8
1.2
1.2
1.5
1.8
2.0
1.8
1.8
1.8
1.8
AgOTf/1.2 K2S2O8/3.6
9
AgF/1.2
AgF/1.5
AgF/1.8
AgF/2.0
AgF/1.8
AgF/1.8
AgF/1.8
AgF/1.8
K2S2O8/3.6
K2S2O8/3.6
K2S2O8/3.6
K2S2O8/3.6
K2S2O8/3.6
K2S2O8/3.6
K2S2O8/3.6
K2S2O8/3.6
10
11
12
13
14
15
16

3
1. (a) Boiko, V. N. Beilstein J. Org. Chem. 2010, 6, 880-921. (b) Tlili， A.;
46.2 ppm) and AgSCF3 (δ = –20.8 ppm) observed as a result
(Scheme 3, Eq. 3).17 Notably, when 4 was treated with AgF in
DMSO at 20 °C for 12 h in the absence of K2S2O8, peaks of 4-
methylbenzenesulfonyl fluoride 12 (δ = –64.8 ppm) and AgSCF3
were observed (Scheme 3, Eq. 4).16
Billard, T. Angew. Chem., Int. Ed. 2013, 52, 6818-6819. (c) Liu, H.; Jiang, X.
Chem. Asian J. 2013, 8, 2546-2563. (d) Toulgoat, F.; Alazet, S.; Billard, T.
Eur. J. Org. Chem. 2014, 2415-2428. (e) Xu, X.-H.; Matsuzaki, K.; Shibata,
N. Chem. Rev. 2015, 115, 731-764. (f) Shao, X.; Xu, C.; Lu, L.; Shen, Q. Acc.
Chem. Res. 2015, 48, 1227-1236.
2. Leo, A.; Hansch, C.; Elkins, D. Chem. Rev. 1971, 71, 525-616.
3. Leroux, F.; Jeschke, P.; Schlosser, M. Chem. Rev. 2005, 105, 827-856.
4. Yagupol’skii, L. M.; Ilchenko, A. Y.; Kondratenko, N. V. Russ. Chem.
Rev. 1974, 43, 32-47.
5. For selected examples: (a) Teverovskiy, G.; Surry, D. S.; Buchwald, S. L.
Angew. Chem. Int. Ed. 2011, 50, 7312-7314. (b) Xiao, Q.; Sheng, J.; Chen, Z.
Y.; Wu, J. Chem. Commun. 2013, 49, 8647-8649. (c) Wang, K. P.; Yun, S.
Y.; Mamidipalli, P.; Lee, D. Chem. Sci. 2013, 4, 3205-3211. (d) Wang, X.;
Zhou, Y.; Ji, G.; Wu, G.; Li, M.; Zhang, Y.; Wang, J. Eur. J. Org. Chem.
2014, 3093-3096. (e) Zhu, S. Q.; Xu, X.-H.; Qing, F. L. Eur. J. Org. Chem.
2014, 4453-4456. (f) Yin, W.; Wang, Z.; Huang, Y. Adv. Synth. Catal. 2014,
356, 2998-3006. (g) Liu, J. B.; Xu, X. H.; Chen, Z. H.; Qing, F. L. Angew.
Chem. Int. Ed. 2015, 54, 897-900.
6. For selected examples: (a) Adams, D. J.; Goddard, A.; Clark, J. H.;
Macquarrie, D. J. Chem. Commun. 2000, 987-988. (b) Lefebvre, Q.; Fava, E.;
Nikolaienko, P.; Rueping, M. Chem. Commun. 2014, 50, 6617-6619. (c)
Nikolaienko, P.; Pluta, R.; Rueping, M. Chem. -Eur. J. 2014, 20, 9867-9870.
(d) Huang, Y.; He, X.; Li, H.; Weng, Z. Eur. J. Org. Chem. 2014, 7324-7328.
7. For selected examples: (a) Orda, V. V.; Yagupolskii, L. M.; Bystrov, V. F.;
Stepanyants, A. U. J. Gen. Chem. 1965, 35, 1628-1635. (b) Clark, J. H.;
Jones, C. W.; Kybett, A. P.; McClinton, M. A. J. Fluorine Chem. 1990, 48,
249-253.
8. For selected examples: (a) Ferry, A.; Billard, T.; Langlois, B. R.; Bacque,
E. J. Org. Chem. 2008, 73, 9362-9365. (b) Shao, X.; Wang, X.; Yang, T.; Lu,
L.; Shen, Q. Angew. Chem. Int. Ed. 2013, 52, 3457-3460. (c) Bootwicha, T.;
Liu, X.; Pluta, R.; Atodiresei, I.; Rueping, M. Angew. Chem. Int. Ed. 2013,
52, 12856-12859. (d) Yang, Y. D.; Azuma, A.; Tokunaga, E.; Yamasaki, M.;
Shiro, M.; Shibata, N. J. Am. Chem. Soc. 2013, 135, 8782-8785. (e)
Vinogradova, E. V.; Muller, P.; Buchwald, S. L. Angew. Chem., Int. Ed.
2014, 53, 3125-3128. (f) Xu, C.; Ma, B.; Shen, Q. Angew. Chem. Int. Ed.
2014, 53, 9316-9320. (g) Rueping, M.; Liu, X.; Bootwicha, T.; Pluta, R.;
Merkens, C. Chem. Commun. 2014, 50, 2508-2511. (h) Alazet, S.; Zimmer,
L.; Billard, T. Chem. Eur. J. 2014, 20, 8589-8593. (i) Huang, Z.; Yang, Y. D.;
Tokunaga, E.; Shibata, N. Org. Lett. 2015, 17, 1094-1097. (j) Xiao, Q.; He,
Q.; Li, J.; Wang, J. Org. Lett. 2015, 17, 6090-6093. (b) Wang, Q.; Qi, Z.; Xie,
F.; Li, X. Adv. Synth. Catal. 2015, 357, 355-360. (k) Shao, X.; Xu, C.; Lu, L.;
Shen, Q. J. Org. Chem. 2015, 80, 3012-3021. (l) Zhang, P. Li, M.; Xue, X.-
S.; Xu, C.; Zhao, Q.; Liu, Y.; Wang, H.; Guo, Y.; Lu, L.; Shen, Q. J. Org.
Chem. 2016, 81, 7486-7509. (m) Chachignon, H.; Maeno, M.; Kondo, H.;
Shibata, N.; Cahard, D. Org. Lett. 2016, 18, 2467-2470. (n) Jiang, L.; Yi, W.;
Liu, Q. Adv. Synth. Catal. 2016, 358, 3700-3705. (o) Lu, K.; Deng, Z.; Li,
M.; Li, T.; Zhao, X. Org. Biomol. Chem. 2017, 15, 1254-1260. (p)
Chachignon, H.; Cahard, D. J. Fluorine Chem. 2017, 198, 82-88. (q) Zhao,
X.; Wei, A.; Yang, B.; Li, T.; Li, Q.; Qiu, D.; Lu, K. J. Org. Chem. 2017, 82,
9175-9181.
Scheme 3. Additional experiments performed to understand the reaction
mechanism.
Based on the available literature9a, 18 and the abovementioned
results, the investigated aryltrifluoromethylthiolation was thought
to proceed as follows (Scheme 4). Initially, 4 reacts with AgF to
form AgSCF3, which is oxidised by K2S2O8 to Ag(II)SCF3, with
decomposition of the latter species affording Ag (I) and F3CS•.
Subsequently, the addition of F3CS• to 9 affords alkyl radical
intermediate A that cyclises to afford aryl radical B. Finally,
•–
oxidation of B by Ag(II) or SO4 followed by deprotonation
affords the desired product 10.
9. For selected examples: (a) Yin, F.; Wang, X.-S. Org. Lett. 2014, 16, 1128-
1131. (b) Zhang, K.; Liu, J.-B.; Qing, F.-L. Chem. Commun. 2014, 50,
14157-14160. (c) Fuentes, N.; Kong, W.; Fern.ndez-S.nchez, L.; Merino, E.;
Nevado, C. J. Am. Chem. Soc. 2015, 137, 964-973. (d) Guo, S.; Zhang, X.;
Tang, P. Angew. Chem. Int. Ed. 2015, 54, 4065-4069. (e) Wu, H.; Xiao, Z.;
Wu, J.; Guo, Y.; Xiao, J.-C.; Liu, C.; Chen, Q.-Y. Angew. Chem. Int. Ed.
2015, 54, 4070-4074. (f) Qiu, Y.-F.; Zhu, X.-Y.; Li, Y.-X.; He, Y.-T.; Yang,
F.; Wang, J.; Hua, H.-L.; Zheng, L.; Wang, L.-C.; Liu, X.-Y.; Liang, Y.-M.
Org. Lett. 2015, 17, 3694-3697.
Scheme 4. Proposed aryltrifluoromethylthiolation mechanism.
10. Honeker, R.; Garza-Sanchez, R. A.; Hopkinson, M. N.; Glorius, F. Chem.
-Eur. J. 2016, 22, 4395-4399.
11. Dagousset, G.; Simon, C.; Anselmi, E.; Tuccio, B.; Billard, T.; Magnier,
E. Chem. -Eur. J. 2017, 23, 4282-4286.
12. Zhu, D.; Shao, X.; Hong, X.; Lu, L.; Shen, Q. Angew. Chem. Int. Ed.
2016, 55, 15807-15811.
13. Li, H.; Shan, C.; Tung, C.; Xu, Z. Chem. Sci. 2017, 8, 2610-2615.
14. For selected examples (a) Zhao, X.; Zhang, L.; Li, T.; Liu, G.; Wang, H.;
Lu, K. Chem. Commun. 2014, 50, 13121-13123. (b) Zhao, X.; Zhang, L.; Lu,
X.; Li, T.; Lu, K. J. Org. Chem. 2015, 80, 2918-2924. (c) Zhao, X.; Li, T.;
Zhang, L.; Lu, K. Org. Biomol. Chem. 2016, 14, 1131-1137. (d) Zhao, X.;
Deng, Z.; Wei, A.; Li, B.; Lu, K. Org. Biomol. Chem. 2016, 14, 7304-7312.
(e) Zhao, X.; Wei, A.; Li, T.; Su, Z.; Chen, J.; Lu, K. Org. Chem. Front,
2017, 4, 232-235. (f) Lu, K.; Deng, Z.; Li, M.; Li, T.; Zhao, X. Org. Biomol.
Chem. 2017, 15, 1254-1260. (g) Zhao, X.; Wei, A.; Yang, B.; Li, T.; Li, Q.;
Qiu, D.; Lu, K. J. Org. Chem. 2017, 82, 9175-9181. (h) Zhao, X.; Li, T.;
Yang, B.; Qiu, D.; Lu, K. Tetrahedron 2017, 73, 3112-3117. (i) Zhao, X.;
Zheng, X.; Tian, M.; Sheng, J.; Tong, Y.; Lu, K. Tetrahedron, 2017, 73,
7233-7238.
3. Conclusion
We have successfully developed silver-mediated radical
aryltrifluoromethylthiolation of activated alkenes by 4-
methylbenzenesulfonothioate as a F3CS radical source to afford
trifluoromethylthiol-substituted oxindoles. The readily accessible
reagents, mild reaction conditions, and broad functional group
compatibility of the above transformation make it an alternative
and practical strategy of constructing Csp3–SCF3 bonds, with the
extension of this strategy to other substrates currently being
investigated in our lab.
Acknowledgments
The authors sincerely thank the financial support from
National Science Foundation of China (Grants 21572158).
15. Li, Y.; Qiu, G.; Wang, H.; Sheng, J. Tetrahedron Lett. 2017, 58, 690-693.
16. General procedure for radical aryltrifluoromethylthiolation of activated
alkenes: To a flame-dried Schlenk tube was added activated alkenes 9 (0.25
mmol), AgF (57 mg, 0.45 mmol), K2S2O8 (243 mg, 0.9 mmol) and dry
DMSO (3 mL). S-trifluoromethyl 4-methylbenzenesulfonothioate (4) (115
References and notes

4
Tetrahedron Letters
mg, 0.45 mmol) was added to the reaction mixture and the mixture was
o
stirred at 20 C for 5-8 h. The mixture was diluted with water (10 mL) and
extracted with ethyl acetate (10 mL × 3). The combined organic phase was
washed with brine, dried over Na2SO4 and concentrated under reduced
pressure to give a residue which was purified by silica gel column
chromatography to afford the pure product.
17. See supporting information for detail.
18. Guo, S.; Cong, F.; Guo, R.; Wang, L.; Tang. P. Nat. Chem. 2017, 9, 546-
551.

5
Highlights
1. Aryltrifluoromethylthiolation
alkenes was achieved.
2. S-trifluoromethyl
of
activated
4-
methylbenzenesulfonothioate was used as F3CS
radical source.
3. Trifluoromethylthiol-substituted oxindoles were
prepared.
4. A silver-mediated radical mechanism was
proposed.