Electrochemical sulfenylation of indoles with disulfides mediated by potassium iodide

Article abstract of DOI:10.1149/2.0071807jes

A novel electrochemical system for sulfenylation of indoles with disulfides to generate 3-sulfenylindoles via C-S bond formation mediated by potassium iodide at a low potential was developed. Iodine was electrogenerated from iodide ions at a graphite anode and showed a high catalytic activity for the electrochemical sulfenylation reactions. A variety of aromatic, heteroaromatic and aliphatic disulfides could react with 2-methlyindole to synthesize the corresponding 3-sulfenylindoles in good to excellent yields. In addition, protected and unprotected indoles with various groups, especially electron-donating groups, also performed well in the sulfenylation reactions. The transformation, which proceeded through the redox of iodine and the generation of intermediate 3-iodoindole, provided an efficient and environmentally benign protocol for the synthesis of 3-sulfenylindoles under mild conditions.

Full text of DOI:10.1149/2.0071807jes

Journal of The Electrochemical Society, 165 (5) G67-G74 (2018)
G67
0013-4651/2018/165(5)/G67/8/$37.00 © The Electrochemical Society
Electrochemical Sulfenylation of Indoles with Disulfides Mediated
by Potassium Iodide
z
Chen Chen, Pengfei Niu, Zhenlu Shen,z and Meichao Li
College of Chemical Engineering, Research Center of Analysis and Measurement, Zhejiang University of Technology,
Hangzhou 310032, People’s Republic of China
A novel electrochemical system for sulfenylation of indoles with disulfides to generate 3-sulfenylindoles via C-S bond formation
mediated by potassium iodide at a low potential was developed. Iodine was electrogenerated from iodide ions at a graphite anode and
showed a high catalytic activity for the electrochemical sulfenylation reactions. A variety of aromatic, heteroaromatic and aliphatic
disulfides could react with 2-methlyindole to synthesize the corresponding 3-sulfenylindoles in good to excellent yields. In addition,
protected and unprotected indoles with various groups, especially electron-donating groups, also performed well in the sulfenylation
reactions. The transformation, which proceeded through the redox of iodine and the generation of intermediate 3-iodoindole, provided
an efficient and environmentally benign protocol for the synthesis of 3-sulfenylindoles under mild conditions.
© 2018 The Electrochemical Society. [DOI: 10.1149/2.0071807jes]
Manuscript submitted January 2, 2018; revised manuscript received March 8, 2018. Published April 17, 2018.
the presence of oxidants have stimulated considerable interest.38–40 In
2016, our group developed an iodine-catalyzed protocol for the syn-
thesis of 3-sulfenylindoles from indoles and thiols using DMSO as
the oxidant.41 It is well-known that iodine can be generated through
electrochemical oxidation from iodide ions at a low potential,42,43
and then serves as a redox mediator in indirect electrosynthesis. In
continuation of our work on the development of electrochemical syn-
thetic methodologies under mild conditions,44–47 herein we reported
an indirect electrochemical system for sulfenylation of indoles with
disulfides to generate 3-sulfenylindoles mediated by potassium iodide
(KI) at a low potential and over-oxidation of disulfides could be effec-
tively inhibited. Cyclic voltammetry and electrolysis techniques were
utilized in the present work to examine the electrocatalytic activity of
iodine. In addition, a plausible mechanism was proposed on the basis
of the identification of the intermediate.
Development of green and efficient methods for the C-S bond for-
mation of the organosulfur compounds has gained much attention in
organic synthesis and material science.1–5 Organosulfur compounds,
such as 3-sulfenylindoles, play an important role due to their thera-
peutic value in the treatment of HIV,6 cancer,7 allergies8 and bacterial
infection.9 Over the past several years, two major synthetic strate-
gies have been developed for preparation of 3-sulfenylindoles. One
protocol was achieved by cyclization reaction of 2-alkynylanilines, 2-
(gem-dibromo(chloro)vinyl)anilines or isocyanides.10–13 Another was
the direct sulfenylation of indoles via C–H functionalization, which
has emerged as a highly attractive and powerful strategy to construct
complicated organosulfur compounds.14–19 A variety of sulfenylating
reagents, such as N-thioiphthalimides, sulfonyl hydrazides, sulfinic
acids, sulfonium salts, thiols and disulfides, have been employed as
the important partners during the reactions. However, many of these re-
actions were catalyzed by transition-metal catalysts such as copper,12
palladium,13 cerium,14 iron15 or vanadium.16 Recently, several ap-
proaches have been developed to access 3-sulfenylindoles without
transition-metal catalysts. Schlosser et al. reported an efficient one-pot
procedure for sulfenylation of 2-carboxyindoles with sulfenyl chlo-
rides generated from thiols in the presence of N-chlorosuccinimide,
but the reactions were carried out at −78◦C.20 The sulfenylation re-
action of indoles with N-(thio)succinimides was studied by Hostier et
al., but 15 equiv. of trifluoroacetic acid was needed as the promoter.21
Bunte salts (RSSO3Na) also have been utilized as the sulfenylat-
ing reagent to prepare 3-sulfenylindoles, but these salts are difficult
to obtain.22,23 Therefore, a green and sustainable method without
transition-metal catalysts, harsh reaction conditions or stoichiomet-
ric amounts of oxidants for the synthesis of 3-sulfenylindoles is still
highly desirable.
Experimental
General
bis(3-chlorophenyl)disulfide,
remarks.—1,2-Bis(2-chlorophenyl)disulfide,
1,2-
1,2-bis(2-methoxyphenyl)disulfide,
1,2-bis(3-methoxyphenyl)disulfide and 1,2-didodecyldisulfane were
prepared in our laboratory according to literature procedures.48 Other
chemicals and solvents were purchased from commercial suppliers
and used without further purification. Gas chromatography (GC) was
performed on an Agilent GC7890A system equipped with a SE-54
capillary column and a flame ionization detector (FID). 1H (500 MHz)
and 13C NMR (125 MHz) were performed on a Bruker Avance III
spectrometer. CDCl3 was used as the solvent with tetramethylsilane
(TMS) as the internal standard.
It is well-known that electrochemical method is an atom economi-
cal and environmentally benign strategy for formation of many organic
compounds, and it can be performed under mild conditions.24–27 In
2016, Zeng et al. reported an indirect electrochemical method to con-
struct C-S bonds of 3-amino-2-thiocyanato-α,β-unsaturated carbonyl
derivatives using 50 mol% NH4Br as the redox mediator.28 Subse-
quently the same group developed a similar methodology to generate
oxindoles in the presence of 10 mol% NH4Br.29 During the course
of this present work, Lei et al. reported a direct electrooxidation of
N-methylindoles with thiols to synthesize 3-sulfenylindoles.30 Their
work was very interesting, but only trace amounts of 3-sulfenylindoles
were obtained when aliphatic thiols were used, because high potentials
might cause the over-oxidation of thiols.31,32
Cyclic voltammetry of sulfenylation.—Cyclic voltammetry exper-
iments were carried out on Vertex Potentiostat/Galvanostat with an
L-type graphite electrode (3 mm in diameter) in a 25 mL undivided
cell. NaBF4 (0.1 mol/L) was used as the supporting electrolyte in
CH3CN solution (15 mL). Another graphite rod (6 mm in diameter,
1 cm in length) was employed as the counter electrode and Ag/Ag+
electrode (0.1 mol/L AgNO3 in CH3CN) as the reference. All the po-
tentials in this work were referred to the Ag/Ag+ reference electrode
(E0 = -77.5 mV vs. ferrocene redox couple).
Electrosynthesis of 3-sulfenylindoles.—The electrochemical ex-
periment was performed on 263A Potentiostat/Galvanostat (Princeton
Applied Research, USA) in a 25 mL undivided cell. Two graphite rods
(6 mm in diameter, 1 cm in length) were employed as the working elec-
trode and the counter electrode respectively. The reference electrode
was Ag/Ag+ electrode (0.1 mol/L AgNO3 in CH3CN). 2-Methyl-
indole (1a, 1.0 mmol), diphenyl disulfide (2a, 0.5 mmol) and KI (0.05
mmol) were added into 0.1 mol/L of NaBF4/CH3CN solution (15 mL)
with stirring at 60◦C. The electrolysis reactions were operated at 0.4 V.
As a nontoxic, cheap and readily available catalyst, iodine has been
widely applied in various organic transformations.33–37 In recent years,
iodine has been known as an important oxidation catalyst for C–S bond
formation reactions, and iodine-catalyzed sulfenylation reactions in
zE-mail: zhenlushen@zjut.edu.cn; limc@zjut.edu.cn
Downloaded on 2018-04-18 to IP 128.122.230.132 address. Redistribution subject to ECS terms of use (see ecsdl.org/site/terms_use) unless CC License in place (see abstract).

G68
Journal of The Electrochemical Society, 165 (5) G67-G74 (2018)
After completion of the reaction (monitored by GC or TLC), the
resulting mixture was concentrated under reduced pressure and pu-
rified by column chromatography on silica gel using hexanes/EtOAc
(100:1) as eluent to afford 2-methyl-3-(phenylthio)-indole (3aa) as a
white solid in 94% yield.
7.16–7.13 (m, 1H), 7.10–7.07 (m, 1H), 6.65-6.59 (m, 3H), 3.70 (s,
3H), 2.53 (s, 3H); 13C NMR (125 MHz, CDCl3): δ = 159.9, 141.2,
140.9, 135.4, 130.3, 129.5, 122.2, 120.7, 119.0, 117.9, 111.2, 110.6,
110.0, 99.2, 55.1, 12.2.
3-((2-methoxyphenyl)thio)-2-methyl-1H-indole
(3aj).—Yield:
Characterization data for products.—2-methyl-3-(phenylthio)-
1H-indole (3aa).—Yield: 94%; White solid; 1H NMR (500 MHz,
CDCl3) δ 8.23 (s, 1H), 7.54 (d, J = 7.8 Hz, 1H), 7.34 (d, J = 8.2 Hz,
1H), 7.21– 7.17 (m, 1H), 7.16–7.11 (m, 3H), 7.04–7.01 (m, 3H), 2.51
(s, 3H); 13C NMR (125 MHz, CDCl3): δ = 141.1, 139.3, 135.4, 130.3,
128.7, 125.5, 124.5, 122.2, 120.7, 119.0, 110.6, 99.4, 12.2.
94%; White solid; 1H NMR (500 MHz, CDCl3) δ 8.31 (s, 1H), 7.55
(d, J = 7.9 Hz, 1H), 7.38 (d, J = 8.0 Hz, 1H), 7.23–7.20 (m, 1H),
7.15–7.12 (m, 1H), 7.06–7.03 (m, 1H), 6.88-6.86 (m, 1H), 6.70-6.67
(m, 1H), 6.53-6.51 (m, 1H), 4.00 (s, 3H), 2.52 (s, 3H); 13C NMR (125
MHz, CDCl3): δ = 155.2, 141.5, 135.6, 130.5, 127.6, 125.4, 125.1,
122.2, 121.1, 120.7, 119.1, 110.6, 110.1, 97.7, 55.9, 12.2.
3-((4-chlorophenyl)thio)-2-methyl-1H-indole (3ab).—Yield: 90%;
White solid; H NMR (500 MHz, CDCl3) δ 8.23 (s, 1H), 7.56 (d,
J = 7.7 Hz, 1H), 7.36 (d, J = 8.2 Hz, 1H), 7.27–7.23 (m, 1H),
7.20–7.18 (m, 1H), 7.17–7.13 (m, 2H), 7.01-6.98 (m, 2H), 2.52 (s,
3H); 13C NMR (125 MHz, CDCl3): δ = 141.2, 137.9, 135.4, 130.2,
130.0, 128.7, 126.7, 122.3, 120.8, 118.8, 110.7, 98.9, 12.1.
2-methyl-3-(p-tolylthio)-1H-indole (3ak).—Yield: 96%; White
solid; 1H NMR (500 MHz, CDCl3) δ 8.18 (s, 1H), 7.54 (d,
J = 7.9 Hz, 1H), 7.32 (d, J = 8.1 Hz, 1H), 7.19–7.16 (m, 1H),
7.13–7.10 (m, 1H), 6.95 (s, 4H), 2.50 (s, 3H), 2.24 (s, 3H); 13C NMR
(125 MHz, CDCl3): δ = 140.9, 135.7, 135.4, 134.3, 130.4, 129.5,
125.3, 122.1, 120.7, 119.0, 110.6, 99.9, 20.8, 12.2.
1
3-((3-chlorophenyl)thio)-2-methyl-1H-indole (3ac).—Yield: 99%;
Yellow oil; 1H NMR (500 MHz, CDCl3) δ 8.14 (s, 1H), 7.66 (d,
J = 7.8 Hz, 1H), 7.37 (d, J = 8.0 Hz, 1H), 7.33–7.30 (m, 1H),
7.28–7.25 (m, 1H), 7.15–7.09 (m, 3H), 7.03-7.01 (m, 1H), 2.50 (s,
3H); 13C NMR (125 MHz, CDCl3): δ = 141.7, 141.5, 135.4, 134.6,
129.9, 129.7, 124.9, 124.7, 123.5, 122.3, 120.8, 118.6, 110.8, 98.1,
11.9.
3-((4-isopropylphenyl)thio)-2-methyl-1H-indole
(3al).—Yield:
90%; White solid; 1H NMR (500 MHz, CDCl3) δ 8.23 (s, 1H), 7.59
(d, J = 7.8 Hz, 1H), 7.36 (d, J = 8.1 Hz, 1H), 7.22–7.19 (m, 1H),
7.16–7.13 (m, 1H), 7.05–7.03 (m, 2H), 7.01-7.00 (m, 2H), 2.86-2.78
(m, 1H), 2.54 (s, 3H), 1.20 (d, J = 6.9 Hz, 6H); 13C NMR (125 MHz,
CDCl3): δ = 145.4, 141.0, 136.1, 135.4, 130.4, 126.9, 125.7, 122.1,
120.6, 119.1, 110.6, 99.9, 33.5, 24.0, 12.2.
3-((2-chlorophenyl)thio)-2-methyl-1H-indole (3ad).—Yield: 92%;
White solid; H NMR (500 MHz, CDCl3) δ 8.33 (s, 1H), 7.53 (d,
4-((2-methyl-1H-indol-3-yl)thio)aniline (3am).—Yield: 92%;
Brown solid; H NMR (500 MHz, CDCl3) δ 8.18 (s, 1H), 7.60 (d,
1
1
J = 7.8 Hz, 1H), 7.39 (d, J = 8.2 Hz, 1H), 7.35–7.34 (m, 1H), 7.25–
7.22 (m, 1H), 7.17–7.14 (m, 1H), 7.01-6.98 (m, 1H), 6.95-6.92 (m,
1H), 6.57-6.55 (m, 1H), 2.53 (s, 3H); 13C NMR (125 MHz, CDCl3):
δ = 141.7, 138.4, 135.6, 130.2, 130.1, 129.3, 126.9, 125.9, 125.2,
122.4, 120.9, 119.0, 110.7, 97.9, 12.2.
J = 7.8 Hz, 1H), 7.32 (d, J = 7.9 Hz, 1H), 7.19–7.16 (m, 1H),
7.15–7.11 (m, 1H), 7.00–6.97 (m, 2H), 6.54-6.52 (m, 2H), 3.54 (s,
2H), 2.55 (s, 3H); 13C NMR (125 MHz, CDCl3): δ = 144.1, 140.3,
135.3, 130.4, 128.6, 127.1, 121.9, 120.5, 119.0, 115.8, 110.5, 12.2.
3-((2-methyl-1H-indol-3-yl)thio)phenol (3an).—Yield: 93%;
Brown solid; H NMR (500 MHz, CDCl3) δ 8.25 (s, 1H), 7.56 (d,
1
3-((4-bromophenyl)thio)-2-methyl-1H-indole (3ae).—Yield: 97%;
White solid; H NMR (500 MHz, CDCl3) δ 8.29 (s, 1H), 7.52 (d,
J = 7.8 Hz, 1H), 7.37 (d, J = 8.0 Hz, 1H), 7.28–7.25 (m, 2H),
7.24–7.21 (m, 1H), 7.17–7.14 (m, 1H), 6.92-6.90 (m, 2H), 2.53 (s,
3H); 13C NMR (125 MHz, CDCl3): δ = 141.2, 138.7, 135.5, 131.6,
130.0, 127.1, 122.4, 120.9, 118.8, 118.0, 110.7, 98.9, 12.2.
1
J = 7.8 Hz, 1H), 7.34 (d, J = 7.9 Hz, 1H), 7.21 (t, J = 7.4 Hz, 1H),
7.17–7.14 (m, 1H), 7.06 (t, J = 8.0 Hz, 1H), 6.71 (d, J = 7.8 Hz,
1H), 6.51 (d, J = 8.1 Hz, 1H), 6.40 (d, J = 1.6 Hz, 1H), 4.70 (t, J =
8.1 Hz, 1H), 2.51 (d, J = 2.7 Hz, 3H); 13C NMR (125 MHz, CDCl3):
δ = 155.9, 141.4, 141.1, 135.4, 130.2, 129.8, 122.2, 120.7, 118.9,
117.9, 112.0, 111.7, 110.8, 98.8, 12.1.
3-((4-fluorophenyl)thio)-2-methyl-1H-indole (3af).—Yield: 90%;
White solid; H NMR (500 MHz, CDCl3) δ 8.26 (s, 1H), 7.55 (d,
1
2-methyl-3-(thiophen-2-ylthio)-1H-indole (3ao).—Yield: 86%;
White solid; H NMR (500 MHz, CDCl3) δ 8.12 (s, 1H), 7.76–7.73
(m, 1H), 7.32– 7.29 (m, 1H), 7.20–7.17 (m, 2H), 7.14–7.13 (m, 1H),
7.07–7.06 (m, 1H), 6.88–6.86 (m, 1H), 2.62 (s, 3H); 13C NMR (125
MHz, CDCl3): δ = 140.0, 138.7, 135.1, 129.8, 128.9, 127.2, 126.7,
122.2, 120.7, 118.8, 110.6, 103.2, 12.2.
1
J = 7.8 Hz, 1H), 7.36 (d, J = 8.0 Hz, 1H), 7.23–7.20 (m, 1H), 7.17–
7.14 (m, 1H), 7.05–7.01 (m, 2H), 6.90-6.85 (m, 2H), 2.55 (s, 3H); 13
C
NMR (125 MHz, CDCl3): δ = 160.8 (d, J = 242.2 Hz), 141.0, 135.4,
134.2, 130.1, 127.4 (d, J = 7.3 Hz), 122.3, 120.8, 118.9, 115.7 (d,
J = 21.9 Hz), 110.6, 99.9, 12.2.
2-methyl-3-((4-nitrophenyl)thio)-1H-indole (3ag).—Yield: 82%;
Yellow solid; 1H NMR (500 MHz, CDCl3) δ 8.46 (s, 1H), 8.03-
8.00 (m, 2H), 7.48 (d, J = 5.7 Hz, 1H), 7.42 (d, J = 8.1 Hz, 1H),
7.28–7.24 (m, 1H), 7.19–7.16 (m, 1H), 7.12–7.10 (m, 2H), 2.54 (s,
3H); 13C NMR (125 MHz, CDCl3): δ = 149.9, 144.8, 141.7, 135.6,
129.6, 124.9, 123.9, 122.7, 121.2, 118.6, 111.0, 97.0, 12.1.
2-methyl-3-(pyridine-2-ylthio)-1H-indole (3ap).—Yield: 95%;
White solid; H NMR (500 MHz, CDCl3) δ 8.70 (s, 1H),8.44-8.42
(m, 1H), 7.56 (d, J = 7.8 Hz, 1H), 7.37 (d, J = 8.0 Hz, 1H), 7.35-7.32
(m, 1H), 7.24–7.20 (m, 1H), 7.17–7.14 (m, 1H), 6.96–6.94 (m, 1H),
6.66 (d, J = 8.2 Hz, 1H), 2.53 (s, 3H); 13C NMR (125 MHz, CDCl3):
δ = 162.8, 149.3, 141.5, 136.6, 135.7, 130.0, 122.3, 120.8, 119.4,
119.1, 118.8, 110.8, 98.1, 12.2.
1
3-((4-methoxyphenyl)thio)-2-methyl-1H-indole
(3ah).—Yield:
96%; White solid; 1H NMR (500 MHz, CDCl3) δ 8.20 (s, 1H), 7.60
(d, J = 7.8 Hz, 1H), 7.33 (d, J = 8.0 Hz, 1H), 7.22–7.19 (m, 1H),
7.17–7.14 (m, 1H), 7.09–7.06 (m, 2H), 6.77-6.74 (m, 2H), 3.75 (s,
3H), 2.54 (s, 3H); 13C NMR (125 MHz, CDCl3): δ = 157.5, 140.6,
135.4, 130.3, 129.9, 127.9, 122.1, 120.6, 118.9, 114.5, 110.6, 100.8,
55.3, 12.1.
2-methyl-3-(propylthio)-1H-indole (3aq).—Yield: 82%; Yellow
oil; H NMR (500 MHz, CDCl3) δ 8.03 (s, 1H), 7.74-7.71 (m, 1H),
7.31-7.28 (m, 1H), 7.22–7.18 (m, 2H), 2.64 (t, J = 5.0 Hz, 2H), 2.54
(s, 3H), 1.58–1.51 (m, 2H), 1.00 (t, J = 7.5 Hz, 3H); 13C NMR (125
MHz, CDCl3): δ = 139.8, 135.2, 130.7, 121.7, 120.2, 118.8, 110.5,
102.6, 38.2, 23.2, 13.3, 12.2.
1
3-((3-methoxyphenyl)thio)-2-methyl-1H-indole
(3ai).—Yield:
3-(dodecylthio)-2-methyl-1H-indole (3ar).—Yield: 65%; Yellow
oil; H NMR (500 MHz, CDCl3) δ 8.01 (s, 1H), 7.75-7.72 (m, 1H),
7.30-7.28 (m, 1H), 7.22–7.19 (m, 2H), 2.67 (t, J = 7.3 Hz, 2H), 2.53
1
90%; White solid; 1H NMR (500 MHz, CDCl3) δ 8.27 (s, 1H), 7.56
(d, J = 7.8 Hz, 1H), 7.35 (d, J = 8.1 Hz, 1H), 7.22–7.19 (m, 1H),
Downloaded on 2018-04-18 to IP 128.122.230.132 address. Redistribution subject to ECS terms of use (see ecsdl.org/site/terms_use) unless CC License in place (see abstract).

Journal of The Electrochemical Society, 165 (5) G67-G74 (2018)
G69
(s, 3H), 1.56–1.50 (m, 2H), 1.43–1.37 (m, 2H), 1.35–1.28 (m, 16H),
0.94 (t, J = 6.9 Hz, 3H); 13C NMR (125 MHz, CDCl3): δ = 139.7,
135.2, 130.6, 121.7, 120.2, 118.8, 110.5, 102.6, 36.3, 31.9, 30.0, 29.6,
29.6, 29.6, 29.6, 29.3, 29.3, 28.6, 22.7, 14.1, 12.1.
0.25
0.20
0.15
0.10
0.05
0.00
3-(benzylthio)-2-methyl-1H-indole (3as).—Yield: 72%; Colorless
oil; 1H NMR (500 MHz, CDCl3) δ 8.00 (s, 1H), 7.70–7.67 (m, 1H),
7.32–7.28 (m, 1H), 7.21–7.16 (m, 5H), 6.98–6.97 (m, 2H), 3.77 (s,
2H), 2.00 (s, 3H); 13C NMR (125 MHz, CDCl3): δ = 141.17, 139.25,
135.28, 130.41, 129.00, 128.06, 126.55, 121.80, 120.30, 118.61,
110.50, 101.34, 40.34, 11.47.
3-(butylthio)-2-methyl-1H-indole (3at).—Yield: 52%; Colorless
oil; 1H NMR (500 MHz, CDCl3) δ 8.07 (s, 1H), 7.72–7.69 (m, 1H),
7.32– 7.28 (m, 1H), 7.20–7.17 (m, 2H), 2.66 (t, J = 1.5 Hz, 2H),
2.55 (s, 3H), 1.53–1.48 (m, 2H), 1.45–1.38 (m, 2H), 0.88(t, J = 1.5
Hz, 3H); 13C NMR (125 MHz, CDCl3): δ = 139.70, 135.23, 130.73,
121.75, 120.19, 118.81, 110.46, 102.77, 35.90, 32.06, 21.74, 13.73,
12.18.
-0.2
0.0
0.2
0.4
0.6
E/V vs. Ag/Ag+
Figure 1. Cyclic voltammograms recorded in 0.1 mol/L NaBF4/CH3CN at
50 mV s−1 scan rate with (a) blank solution; (b) KI (0.05 mmol); (c) KI (0.05
mmol) and 2a (0.5 mmol); (d) 1a (1 mmol) and 2a (0.5 mmol); (e) KI (0.05
mmol), 1a (1 mmol) and 2a (0.5 mmol); (f) KI (0.05 mmol) and 1a (1 mmol).
1-methyl-3-(phenylthio)-1H-indole (3ba).—Yield: 92%; White
solid; 1H NMR (500 MHz, CDCl3) δ 7.68 (d, J = 8.0 Hz, 1H),
7.43 (d, J = 8.3 Hz, 1H), 7.36– 7.34 (m, 2H), 7.24–7.21 (m, 1H),
7.21–7.19 (m, 2H), 7.17–7.15 (m, 2H), 7.11–7.08 (m, 1H), 3.86 (s,
3H); 13C NMR (125 MHz, CDCl3): δ = 139.7, 137.5, 135.0, 129.8,
128.6, 125.7, 124.7, 122.5, 120.5, 119.7, 109.7, 100.5, 33.1.
5-methyoxy-3-(phenylthio)-1H-indole (3ea).—Yield: 84%; White
1
solid; H NMR (500 MHz, CDCl3) δ 8.36 (s, 1H), 7.46 (d, J = 2.6
Hz, 1H), 7.33 (d, J = 8.8 Hz, 1H), 7.20 (t, J = 7.7 Hz, 2H), 7.13 (d,
J = 7.6 Hz, 2H), 7.10–7.07 (m, 2H), 6.96–6.94 (m, 1H), 3.81 (s, 3H);
13C NMR (125 MHz, CDCl3): δ = 155.2, 139.3, 131.4, 131.3, 130.0,
128.7, 125.7, 124.7, 113.6, 112.4, 102.3, 100.8, 55.8.
3-((4-chlorophenyl)thio)-1-methyl-1H-indole (3bb).—Yield: 95%;
White solid; 1H NMR (500 MHz, CDCl3) δ 7.62 (d, J = 7.9 Hz, 1H),
7.43 (d, J = 8.3 Hz, 1H), 7.37–7.33 (m, 2H), 7.24–7.20 (m, 1H),
7.16–7.13 (m, 2H), 7.07–7.04 (m, 2H), 3.87 (s, 3H); 13C NMR (125
MHz, CDCl3): δ = 138.3, 137.6, 135.1, 130.4, 129.5, 128.7, 127.0,
122.7, 120.64, 119.5, 109.8, 100.1, 33.1.
1-methyl-2-phenyl-3-(phenylthio)-1H-indole (3fa).—Yield: 92%;
White solid; 1H NMR (500 MHz, CDCl3) δ 7.71 (d, J = 7.9 Hz,
1H), 7.52–7.46 (m, 6H), 7.40–7.37 (m, 1H), 7.28–7.24 (m, 1H),
7.21–7.18 (m, 2H), 7.12–7.06 (m, 3H), 3.79 (s, 3H); 13C NMR (125
MHz, CDCl3): δ = 145.9, 140.0, 137.6, 130.6, 130.5, 129.7, 128.7,
128.6, 128.2, 125.5, 124.4, 122.8, 120.9, 119.8, 109.8, 99.6, 31.7.
1-methyl-3-(p-tolylthio)-1H-indole (3bj).—Yield: 83%; White
solid; 1H NMR (500 MHz, CDCl3) δ 7.60 (d, J = 8.0 Hz, 1H), 7.32
(d, J = 8.3 Hz, 1H), 7.27–7.24 (m, 2H), 7.17–7.12 (m, 1H), 7.01 (d,
J = 8.3 Hz, 2H), 6.93 (d, J = 8.2 Hz, 2H), 3.74 (s, 3H), 2.21 (s, 3H);
13C NMR (125 MHz, CDCl3): δ = 137.5, 136.0, 134.9, 134.5, 129.9,
129.5, 126.2, 122.5, 120.4, 119.8, 109.7, 101.2, 33.0, 20.9.
5-bromo-3-(phenylthio)-1H-indole (3ga).—Yield: 67%; White
solid; 1H NMR (500 MHz, CDCl3) δ 8.47 (s, 1H), 7.78 (s, 1H),
7.50 (d, J = 2.5 Hz, 1H), 7.38– 7.36 (m, 1H), 7.32 (d, J = 8.2 Hz,
1H) 7.21 (t, J = 5.2 Hz, 2H), 7.10 (t, J = 4.1 Hz, 3H); 13C NMR (125
MHz, CDCl3): δ = 138.7, 135.1, 131.9, 131.0, 128.8, 126.1, 125.9,
125.1, 122.2, 114.5, 113.1, 102.8.
3-(phenylthio)-1H-indole (3ca).—Yield: 86%; White solid; 1H
NMR (500 MHz, CDCl3) δ 8.36 (s, 1H), 7.61 (d, J = 8.0 Hz, 1H),
7.47 (d, J = 2.6 Hz, 1H), 7.42 (d, J = 8.2 Hz, 1H), 7.28– 7.24 (m, 1H),
7.18–7.14 (m, 3H), 7.11–7.09 (m, 2H), 7.06–7.03 (m, 1H); 13C NMR
(125 MHz, CDCl3): δ = 139.2, 136.5, 130.7, 129.1, 128.7, 125.9,
124.8, 123.1, 120.9, 119.7, 111.6, 102.9.
3-iodo-2-methyl-1H-indole (4).—Yield: 15%; Brown oil; 1H NMR
(500 MHz, CDCl3) δ 8.13 (s, 1H), 7.39– 7.38 (m, 1H), 7.28–7.25 (m,
1H), 7.22–7.17 (m, 2H), 2.49 (s, 3H); 13C NMR (125 MHz, CDCl3):
δ = 136.3, 135.9, 130.9, 122.4, 120.6, 120.3, 110.6, 59.1, 14.5. MS
(EI), m/z 260.17 [M+, 100%].
5-methyl-3-(phenylthio)-1H-indole (3da).—Yield: 95%; White
1
solid; H NMR (500 MHz, CDCl3) δ 8.33 (s, 1H), 7.46 (d, J = 2.5
Hz, 1H), 7.44 (s, 1H), 7.35 (d, J = 8.3 Hz, 1H), 7.20– 7.17 (m, 2H),
7.13–7.11 (m, 3H), 7.09–7.06 (m, 1H), 2.44 (s, 3H); 13C NMR (125
MHz, CDCl3): δ = 139.5, 134.8, 130.9, 130.4, 129.4, 128.7, 125.7,
124.7, 124.7, 119.2, 111.2, 102.0, 21.5.
Results and Discussion
Cyclic voltammetric study of sulfenylation.—Electrochemical
sulfenylation of 2-methylindole (1a) with diphenyl disulfide (2a) me-
diated by KI in 0.1 mol/L NaBF4/CH3CN solution was studied by
cyclic voltammetry. As shown in curve a of Fig. 1, cyclic voltammo-
grams were recorded in NaBF4/CH3CN blank solution, and no redox
wave was observed at potentials ranged from −0.2 V to 0.6 V. With
the addition of KI (0.05 mmol) into the blank solution, two typical
oxidation peaks of iodide ions were displayed at about 0.08 V and
0.37 V (curve b), which corresponded to the oxidation of iodide ion to
form triiodide ion (Eq. 1) and the oxidation of triiodide ion to produce
molecular iodine (Eq. 2):49
3-((4-chlorophenyl)thio)-5-methyl-1H-indole (3db).—Yield: 93%;
1
White solid; H NMR (500 MHz, CDCl3) δ 8.34 (s, 1H), 7.46 (d,
J = 2.6 Hz, 1H), 7.40 (s, 1H), 7.35 (d, J = 8.4 Hz, 1H), 7.16–7.13 (m,
3H), 7.05–7.03 (m, 2H), 2.45 (s, 3H); 13C NMR (125 MHz, CDCl3):
δ = 138.1, 134.8, 130.9, 130.6, 130.4, 129.1, 128.8, 126.9, 124.9,
119.0, 111.3, 101.6, 21.5.
5-methyl-3-(p-tolylthio)-1H-indole (3dj).—Yield: 94%; White
solid; 1H NMR (500 MHz, CDCl3) δ 8.28 (s, 1H), 7.45–7.44 (m,
2H), 7.33 (d, J = 8.3 Hz, 1H), 7.12–7.10 (m, 1H), 7.06–7.04 (m, 2H),
7.01 (d, J = 8.2 Hz, 2H), 2.44 (s, 3H), 2.28 (s, 3H); 13C NMR (125
MHz, CDCl3): δ = 135.8, 134.8, 134.5, 130.7, 130.3, 129.5, 129.4,
126.0, 124.6, 119.2, 111.2, 102.6, 21.4, 20.9.
3I− − 2e− → I3−
[1]
2I3− − 2e− → 3I2
[2]
Downloaded on 2018-04-18 to IP 128.122.230.132 address. Redistribution subject to ECS terms of use (see ecsdl.org/site/terms_use) unless CC License in place (see abstract).

G70
Journal of The Electrochemical Society, 165 (5) G67-G74 (2018)
Table I. Optimization of electrolytic conditionsa.
Entry
KI (mol%)
Potential (V)
Electrode
Temperature (◦C)
Time (h)
Conv.b,c (%)
Select.c,d (%)
1
2
3
4
5
6
7
8
9
5
3
0
5
5
5
5
5
5
0.6
0.6
0.6
0.6
0.4
0.4
0.2
0.4
0.4
Pt
Pt
Pt
C
C
C
C
C
C
60
60
60
60
60
60
60
40
25
5
5
5
5
5
6
6
6
6
99
42
trace
99
93
99
58
64
27
99
85
–
99
99
99
98
99
99
aElectrolytic conditions: 1a (1 mmol), 2a (0.5 mmol), 0.1 mol/L NaBF4/CH3CN solution (15 mL), undivided cell.
bConversion of 1a.
cDetermined by GC with peak area normalization method.
dSelectivity to 3aa.
In order to investigate the catalytic ability of iodine for the electro-
chemical sulfenylation reaction, 0.5 mmol 2a and 1.0 mmol 1a were
added into the above solution respectively. As a comparison with
curve b, the peak currents didn’t change obviously in the presence of
2a (curve c), which revealed that 2a showed almost no voltammetric
response at the electrode. While 1a was added to the solution, the
second oxidation peak at about 0.37 V increased dramatically (curve
f). It demonstrated that iodine, which electrogenerated from triiodide
ion at the anode, has reacted with 1a rather than 2a in 0.1 mol/L
NaBF4/CH3CN solution. With the consumption of 1a, the oxidation
current of triiodide ion to iodine was greatly promoted and the reduc-
tion current decreased. When 1a and 2a were added into the solution
simultaneously, almost the same cyclic voltammogram as curve f was
observed (curve e). It suggested that an intermediate might be gener-
ated from iodine and 1a, and then reacted with 2a through chemical
process to generate a new compound.50,51 The conductivity of the
solution decreased a little with the addition of substrates, and the ox-
idation peak potentials of curve e shifted positively as compared with
curve f.
In addition, the oxidation currents of curves e and f increased
rapidly when the potential was more than 0.5 V. To analyze the
cyclic voltammograms more clearly, the experiment in 0.1 mol/L
NaBF4/CH3CN with 1a and 2a in the absence of the mediator KI
was also carried out (curve d). As shown in curve d, the oxidation
current of 1a began to increase at about 0.4 V to form indole radical
cation.52 However, iodide ion as a nucleophilic reagent, could attack
indole radical cation to produce 3-iodo-indole, and the electropoly-
merization of indole was inhibited effectively as shown in curves e
and f.53 Therefore, a low and suitable potential should be chosen for
the electrochemical reactions.
Thus 0.4 V was chosen for the constant potential electrolysis, which
was in good agreement with the results of cyclic voltammetry. The
sulfenylation reactions have also been performed at 40◦C and room
temperature (25◦C) under the above optimized conditions. However,
only 64% and 27% conversions of 1a were obtained after 6 h (entries
8 and 9), and 60◦C might be better for the sulfenylation reactions.
To further study the electrolysis progress, the sulfenylation reaction
of 1a with 2a was monitored by gas chromatography (GC) once an
hour (Fig. 2). During the electrolysis, 1a and 2a reduced gradually and
the desired product 3aa was formed with time. After 6 h of electrolysis,
the GC yield of 3aa was 99% and the Faradic efficiency was about
87%. As we expected, 1a and 2a were successfully converted into 3aa
in the presence of KI at a low potential of 0.4 V.
Scope of sulfenylation of indoles with disulfides.—The general
applicability of the catalytic system for sulfenylation of 1a with
various disulfide derivatives was investigated. Isolated yields of the
products were obtained during the electrochemical sulfenylation of
1a (1.0 mmol ) with disulfide derivatives (0.5 mmol) in 0.1 mol/L
NaBF4/CH3CN solution (15 mL) in the presence of KI (5 mol%),
as shown in Scheme 1. 3aa was obtained from 1a and 2a under
the optimized conditions with 94% isolated yield. It was found that
diphenyl disulfides with halide groups such as chloro (o-, m-, p-
), bromo, and fluoro on benzene ring could react with 1a steadily
and the isolated yields of 3-sulfenylindoles were higher than 90%
(3ab-3af). 4-Nitrophenyl disulfide and 1a could smoothly transformed
100
80
60
40
20
0
Optimization of electrolysis conditions.—In an endeavor to
achieve the optimized conditions for electrochemical sulfenylation
reactions, 1a and 2a were chosen as the model substrates to generate
the corresponding product 3aa and the results were shown in Table I.
When 0.6 V was chosen as the potential for a controlled potential
electrolysis at Pt electrode (entry 1), excellent conversion of 1a (99%)
and selectivity to 3aa (99%) were obtained in the presence of 5 mol%
KI. To our delight, polymerization reaction of 1a was not obvious. The
conversion was decreased to 42% when KI was reduced to 3 mol%
(entry 2), and only trace amounts of the desired product was observed
in the absence of KI (entry 3). It showed that iodine played an im-
portant role in the electrochemical sulfenylation reaction. Therefore,
5 mol% KI was applied for all the substrates in the following elec-
trochemical experiments. When inexpensive graphite rods took the
place of Pt electrodes, it also showed excellent performance for the
sulfenylation reaction under the similar conditions (entry 4). When the
potential was reduced to 0.4 V or 0.2 V, the conversion of 1a decreased
slightly (entries 5 and 7). With the reaction time prolonged to 6 h at
0.4 V, 99% conversion and 99% selectivity were obtained (entry 6).
-1
0
1
2
3
4
5
6
7
t / h
Figure 2. Effect of reaction time on indole conversion and product yield.
Reaction conditions: 0.1 mol/L NaBF4/CH3CN (15 mL), 1a (1.0 mmol), 2a
(0.5 mmol), KI (0.05 mmol), 0.4 V, 60◦C, 6 h. Conversion and yield were
determined by GC with area normalization method.
Downloaded on 2018-04-18 to IP 128.122.230.132 address. Redistribution subject to ECS terms of use (see ecsdl.org/site/terms_use) unless CC License in place (see abstract).

Journal of The Electrochemical Society, 165 (5) G67-G74 (2018)
G71
Scheme 1. Reactions of 1a with various disulfides. The reactions were carried out with 1a (1 mmol), 2 (0.5 mmol) and KI (0.05 mmol) in 0.1 mol/L NaBF4/CH3CN
solution (15 mL) at 60◦C. Yield of isolated product 65–97%.
to the desired product 3ag in 82% yield. Diphenyl disulfides with
methoxy group in ortho, meta and para positions also underwent
smooth transformations to generate the desired products in excellent
isolated yields (3ah-3aj). Furthermore, electron-donating groups such
as methyl, isopropyl, amino, and hydroxyl in para positions performed
well in this transformation with the yields higher than 90% (3ak-3an).
These results revealed that aromatic disulfides with either electron-
withdrawing or electron-donating groups could react with 1a and give
the corresponding 3-sulfenylindoles in good to excellent yields. In
addition, we were delighted to disclose that similar sulfenylation re-
actions, using heteroaromatic disulfides including 2-thienyl disulfide
and 2,2’-dithiodipyridine as sulfenylating agents, were also performed
successfully under present reaction conditions (3ao-3ap). Aliphatic
disulfides, such as dipropyl disulfide, 1,2-didodecyldisulfane and 1,2-
dibenzyldisulfane, also could react with 1a to generate the desired
products in good yields (3aq-3as).
Next, we explored the scope of indole derivatives. As shown
in Scheme 2, 1-methylindole has been successfully employed in
this process, and the isolated yields of products were more than
83% (3ba-3bj). The standard conditions were also applied to in-
dole, but the reaction time should be prolonged to 12 h to achieve
high product yield (3ca). The presence of electron donating groups
(methyl, methoxy) on the benzene ring of indoles underwent con-
version to produce the corresponding 3-sulfenylindoles in good
to excellent yields (3da-3ea). Steric effects did not play an im-
portant role in the isolated yield when a phenyl group was in-
troduced in the C-2 position of indole (3fa). However, it ap-
peared that indoles with electron-withdrawing groups became slug-
gish. For example, the reaction of 5-bromoindole and 2a gave
only 67% yield of the desired product 3ga even the poten-
tial was up to 0.6 V and the reaction time was prolonged to
20 h.
Downloaded on 2018-04-18 to IP 128.122.230.132 address. Redistribution subject to ECS terms of use (see ecsdl.org/site/terms_use) unless CC License in place (see abstract).

G72
Journal of The Electrochemical Society, 165 (5) G67-G74 (2018)
Scheme 2. Scope of indole derivatives. The reactions were carried out with 1 (1 mmol), 2 (0.5 mmol) and KI (0.05 mmol) in 0.1 mol/L NaBF4/CH3CN solution
(15 mL) at 60◦C. Yield of isolated product 67–95%. a0.6 V.
To evaluate the scalability of this electrocatalytic system, the
sulfenlation reaction of 1a and 2a was performed on a gram-scale
(Scheme 3). To our delight, the desired product 3aa was obtained in
85% isolated yield (1.0 g). The result showed the great potential of
this electrochemical method in practical synthesis.
In addition, when 1 equiv. of (2,2,6,6-tetramethylpiperidin-1-yl)oxy
(TEMPO) was added as the radical scavenger28,30,54 in 0.1 mol/L
NaBF4/CH3CN solution with 1a (1.0 mmol), 2a (0.5 mmol) and KI
(0.05 mmol) under the standard conditions, only 37% GC yield of
3aa was obtained (Eq. 6). In our previous report,41 when stoichio-
metric TEMPO was added into the reaction solution of indole and
1,2-diphenyldisulfane in the presence of 5 mol% I2 with DMSO as the
terminal oxidant, the GC yield of sulfenylation product was decreased
from 97% to 30%. These results revealed that radical intermediates
might be involved in this transformation. In order to investigate the
catalytic ability of iodine more clearly, KI was replaced by stoichio-
metric I2, and 99% GC yield of 3aa was obtained (Eq. 7). According
to literatures,55,56 PhSI could be generated in situ from 2a and I2. Thus
the control experiment of 2a and I2 was carried out, and fortunately,
PhSI was observed by GC-MS analysis (Eq. 8). Then 1a (1 mmol)
was added into the above solution, and 99% GC yield of 3aa was
Mechanism investigation.—According to the cyclic voltammetry
analysis of Fig. 1, an intermediate might be generated from 1a and
iodine. To gain further insight into the reaction mechanism, several
control experiments were carried out (Scheme 4). To make 1a be
fully converted at a constant potential of 0.4 V, 2 equiv. of KI was
added into 0.1 mol/L NaBF4/CH3CN solution (Eq. 3). However, in-
termediate 3-iodo-2-methyl-indole (4) was unstable and its isolated
yield was only 15%.50,51 No desired product 3aa was observed with-
out electric current (Eq. 4). Then 4 successfully reacted with 2a in
the absence of KI to synthesize 3aa in 88% isolated yield (Eq. 5).
Scheme 3. Gram-scale synthesis.
Downloaded on 2018-04-18 to IP 128.122.230.132 address. Redistribution subject to ECS terms of use (see ecsdl.org/site/terms_use) unless CC License in place (see abstract).

Journal of The Electrochemical Society, 165 (5) G67-G74 (2018)
G73
Scheme 4. Control experiments for mechanism.
aStandard conditions: 0.1 mol/L NaBF4/CH3CN (15 mL), 1a (1 mmol) or 2a
(0.5 mmol), 60◦C, 6 h.
bIsolated yield.
cReaction time: 4 h.
dYield was determined by GC with area normalization method.
Scheme 5. Proposed reaction mechanism for electrosynthesis of
3-sulfenylindoles.
obtained which suggested that PhSI was the reaction intermediate of
2a and I2.
Based on above observations, a plausible mechanism for electro-
chemical sulfenylation of 2-methylindole with diphenyl disulfide has
been proposed is illustrated in Scheme 5. Initially, iodide ion is elec-
trooxidized to the molecular iodine. As soon as it is generated at the
anode surface, electrophilic addition of iodine to the C-3 position
of 2-methylindole produces intermediate 3-iodo-2-methyl-indole (4)
and releases iodide ion which can be oxidized in the following re-
dox cycle. Subsequently, thio radical which is formed from diphenyl
disulfide reacts with 4 to generate a radical intermediate 5. Then
the desired product 2-methyl-3-(phenylthio)-indole can be produced
from the radical intermediate 5. Meanwhile, iodine radical is released
which would be turned to molecular iodine. It is evidenced that the
color of the solution turned dark gradually in the reaction of 4 and
diphenyl disulfide (Scheme 4, Eq. 5). At the same time, hydrogen ions
are reduced to H2 at the cathode (Scheme 5, path a). However, the
radical scavenger TEMPO cannot inhibit the sulfenylation reaction
completely (Scheme 4, Eq. 6). It means that multiple pathways may
be involved in this transformation. Diphenyl disulfide can react with
molecular iodine to produce PhSI, which attacks the C-3 position of
2-methylindole to form intermediate 6. Then 6 is deprotonated, and
the product 2-methyl-3-(phenylthio)-indole is generated (Scheme 5,
path b).19,38–40
Thiols have also been utilized as the attractive sulfenylating
reagents.16,30,41 Therefore, reactions of 1a with some thiols to generate
3-sulfenylindoles were carried out under the optimized conditions. As
shown in Scheme 6, 4-chlorobenzenethiol, 4-methoxybenzenethiol,
thiophene-2-thiol and butane-1-thiol were used as the substrates, and
the corresponding products were obtained in good yields (3ab, 3ah,
3ao, 3at).
Scheme 6. Reactions of 1a with thiols. The reactions were carried out with 1a (1 mmol), thiols (1 mmol) and KI (0.05 mmol) in 0.1 mol/L NaBF4/CH3CN
solution (15 mL) at 60◦C. Yield of isolated product 52–88%.
Downloaded on 2018-04-18 to IP 128.122.230.132 address. Redistribution subject to ECS terms of use (see ecsdl.org/site/terms_use) unless CC License in place (see abstract).

G74
Journal of The Electrochemical Society, 165 (5) G67-G74 (2018)
Conclusions
15. X. L. Fang, R. Y. Tang, P. Zhong, and J. H. Li, Synthesis, 4183 (2009).
16. Y. Maeda, M. Koyabu, T. Nishimura, and S. Uemura, J. Org. Chem., 69, 7688 (2004).
17. F. L. Yang and S. K. Tian, Angew. Chem. Int. Ed., 52, 4929 (2013).
18. C. R. Liu and L. H. Ding, Org. Biomol. Chem., 13, 2251 (2015).
19. F. Xiao, H. Xie, S. Liu, and G. J. Deng, Adv. Synth. Catal., 356, 364 (2014).
20. K. M. Schlosser, A. P. Krasutsky, H. W. Hamilton, J. E. Reed, and K. Sexton, Org.
lett., 6, 819 (2004).
In summary, an efficient KI-catalyzed electrosynthesis of
3-sulfenylindoles at a low potential have been developed. The elec-
tropolymerization of indoles and over-oxidation of disulfides were
effectively inhibited in this electrochemical system. High electro-
catalytic activity of iodine for sulfenylation of indoles with disul-
fides was disclosed by cyclic voltammetry measurements. With this
method, various indoles could react with aromatic, heteroaromatic and
aliphatic disulfides to generate the corresponding products in good to
excellent yields. In addition, several thiols also performed well in
the sulfenylation reactions under the optimized condition. According
to cyclic voltammetry studies and control experiments, a plausible
mechanism was proposed.
21. T. Hostier, V. Ferey, G. Ricci, D. Gomez Pardo, and J. Cossy, Chem. Commun., 51,
13898 (2015).
22. J. Li, Z. J. Cai, S. Y. Wang, and S. J. Ji, Org. Biomol. Chem., 14, 9384 (2016).
23. H. Qi, T. Zhang, K. Wan, and M. Luo, J. Org. Chem., 81, 4262 (2016).
24. J. Yoshida, K. Kataoka, R. Horcajada, and A. Nagaki, Chem. Rev., 108, 2265 (2008).
25. B. Elsler, D. Schollmeyer, K. M. Dyballa, R. Franke, and S. R. Waldvogel, Angew.
Chem. Int. Ed., 53, 5210 (2014).
26. T. Morofuji, A. Shimizu, and J. Yoshida, J. Am. Chem. Soc., 135, 5000 (2013).
27. R. Francke and R. D. Little, Chem. Soc. Rev., 43, 2492 (2014).
28. L. S. Kang, M. H. Luo, C. M. Lam, L. M. Hu, R. D. Little, and C. C. Zeng, Green
Chem., 18, 3767 (2016).
29. Y. Y. Jiang, S. Liang, C. C. Zeng, L. M. Hu, and B. G. Sun, Green Chem., 18, 6311
(2016).
Acknowledgments
30. P. Wang, S. Tang, P. F. Huang, and A. W. Lei, Angew. Chem. Int. Ed., 56, 3009 (2017).
31. S. Madabhushi, R. Jillella, V. Sriramoju, and R. Singh, Green Chem., 16, 3125 (2014).
32. G. K. S. Prakash, T. Mathew, C. Panja, and G. A. Olah, J. Org. Chem., 72, 5847
(2007).
33. P. T. Parvatkar, P. S. Parameswaran, and S. G. Tilve, Chem. Eur. J., 18, 5460 (2012).
34. L. Royer, S. K. De, and R. A. Gibbs, Tetrahedron Lett., 46, 4595 (2005).
35. R. S. Bhosale, S. V. Bhosale, S. V. Bhosale, T. Wang, and P. K. Zubaidha, Tetrahedron
Lett., 45, 9111 (2004).
36. P. Finkbeiner and B. J. Nachtsheim, Synthesis, 45, 979 (2013).
37. A. N. Vereshchagin, M. N. Elinson, E. O. Dorofeeva, I. S. Bushmarinov,
S. V. Gorbunov, P. A. Belyakov, A. O. Chizhov, and G. I. Nikishin, J. Mol. Catal. A:
Chem., 363–364, 69 (2012).
We are grateful for the generous financial support of the National
Natural Science Foundations of China (21773211, 21776260 and
21376224) and the Natural Science Foundation of Zhejiang Province
(LY17B060007).
ORCID
Meichao Li https://orcid.org/0000-0001-8808-2554
38. W. Ge and Y. Wei, Green Chem., 14, 2066 (2012).
References
39. M. A. Hiebel and S. Berteina-Raboin, Green Chem., 17, 937 (2015).
40. H. Zhang, X. Bao, Y. Song, J. Qu, and B. Wang, Tetrahedron, 71, 8885 (2015).
41. S. L. Yi, M. C. Li, W. M. Mo, X. Q. Hu, B. X. Hu, N. Sun, L. Q. Jin, and Z. L. Shen,
Tetrahedron Lett., 57, 1912 (2016).
42. C. Zhang, Y. Chen, and G. Yuan, Chin. J. Chem., 34, 1277 (2016).
43. N. Yang, Q. Lai, H. Jiang, and G. Yuan, Electrochem. Commun., 72, 109 (2016).
44. X. J. Yang, Z. Q. Fan, Z. L. Shen, and M. C. Li, Electrochim. Acta, 226, 53 (2017).
45. J. J. Lu, J. Q. Ma, J. M. Yi, Z. L. Shen, Y. J. Zhong, C. A. Ma, and M. C. Li, Elec-
trochim. Acta, 130, 412 (2014).
46. Q. G. Chen, C. J. Fang, Z. L. Shen, and M. C. Li, Electrochem. Commun., 64, 51
(2016).
47. Z. Q. Fan, X. J. Yang, C. Chen, Z. L. Shen, and M. C. Li, J. Electrochem. Soc., 164,
G54 (2017).
48. S. L. Yi, M. C. Li, X. Q. Hu, W. M. Mo, and Z. L. Shen, Chin. Chem. Lett., 27, 1505
(2016).
49. V. A. Macagno, M. C. Giordano, and A. J. Arvia, Electrochim. Acta, 14, 335 (1969).
50. L. Liu, Y. Y. Xu, Z. Q. Yang, J. N. Xiang, and G. Y. Xu, Chin. Chem. Lett., 23, 1230
(2012).
51. X. Pang, L. Xiang, J. Ma, X. Yang, and R. Yan, RSC Adv., 6, 111713 (2016).
52. D. Nematollahi, S. Momeni, and S. Khazalpour, Electrochim. Acta, 147, 310 (2014).
53. M. Saraji and A. Bagheri, Synthetic Met., 98, 57 (1998).
54. P. Lee, P. Liang, and W. Yu, Org. Lett., 19, 2082 (2017).
55. P. Mampuys, Y. Zhu, S. Sergeyev, E. Ruijter, R. V. A. Orru, S. V. Doorslaer, and
B. U. W. Maaes, Org. Lett., 18, 2808 (2016).
1. S. Ranjit, R. Lee, D. Heryadi, C. Shen, J. Wu, P. Zhang, K. W. Huang, and X. Liu, J.
Org. Chem., 76, 8999 (2011).
2. Y. Xu, X. Tang, W. Hu, W. Wu, and H. Jiang, Green Chem., 16, 3720 (2014).
3. A. K. Bagdi, S. Mitra, M. Ghosh, and A. Hajra, Org. Biomol. Chem., 13, 3314 (2015).
4. X. Wang, R. Qiu, C. Yan, V. P. Reddy, L. Zhu, X. Xu, and S. F. Yin, Org. Lett., 17,
1970 (2015).
5. R. Rahaman, N. Devi, and P. Barman, Tetrahedron Lett., 56, 4224 (2015).
6. G. L. Regina, M. C. Edler, A. Brancale, S. Kandil, A. Coluccia, F. Piscitelli, E. Hamel,
G. D. Martino, R. Matesanz, J. F. D´ıaz, A. I. Scovassi, E. Prosperi, A. Lavecchia,
E. Novellino, M. Artico, and R. Silvestri, J. Med. Chem., 50, 2865 (2007).
7. R. Silvestri, G. D. Martino, G. L. Regina, M. Artico, S. Massa, L. Vargiu, M. Mura,
A. G. Loi, T. Marceddu, and P. L. Colla, J. Med. Chem., 46, 2482 (2003).
8. P. C. Unangst, D. T. Connor, S. R. Stabler, R. J. Weikert, M. E. Carethers,
J. A. Kennedy, D. O. Thueson, J. C. Chestnut, R. L. Adolphson, and M. C. Conroy,
J. Med. Chem., 32, 1360 (1989).
9. S. S. Khandekar, D. R. Gentry, G. S. Van Aller, P. Warren, H. Xiang, C. Silverman,
M. L. Doyle, P. A. Chambers, A. K. Konstantinidis, M. Brandt, R. A. Daines, and
J. T. Lonsdale, J. Boil. Chem., 276, 30024 (2001).
10. T. Mitamura, K. Iwata, and A. Ogawa, J. Org. Chem., 76, 3880 (2011).
11. J. Liu, P. Li, W. Chen, and L. Wang, Chem. Commun., 48, 10052 (2012).
12. Z. Li, L. Hong, R. Liu, J. Shen, and X. Zhou, Tetrahedron Lett., 52, 1343 (2011).
13. Y. J. Guo, R. Y. Tang, J. H. Li, P. Zhong, and X. G. Zhang, Adv. Synth. Catal., 351,
2615 (2009).
56. H. A. Du, R. Y. Tang, C. L. Deng, Y. Liu, J. H. Li, and X. G. Zhang, Adv. Synth.
14. E. Marcantoni, R. Cipolletti, L. Marsili, S. Menichetti, R. Properzi, and C. Viglianisi,
Eur. J. Org. Chem., 132 (2013).
Catal., 353, 2739 (2011).
Downloaded on 2018-04-18 to IP 128.122.230.132 address. Redistribution subject to ECS terms of use (see ecsdl.org/site/terms_use) unless CC License in place (see abstract).