Cu-catalysed direct bis-thiolation of benzoheterocycles with arylsulfonyl hydrazides

Article abstract of DOI:10.3184/174751918X15350179602459

A series of bis-arylsulfenylated indoles (10), benzofurans (3), and benzothiophenes (3) and of monosulfenylated indoles (5), 12 of which are novel, were prepared in good yields via a Cu-catalysed direct sulfenylation of benzoheterocycles with arylsulfonyl hydrazides. Sulfonothioates are probably the major thiolated intermediates in this transformation.

Full text of DOI:10.3184/174751918X15350179602459

456 RESEARCH PAPER
VOL. 42 SEPTEMBER, 456–462
JOURNAL OF CHEMICAL RESEARCH 2018
Cu-catalysed direct bis-thiolation of benzoheterocycles with arylsulfonyl
hydrazides
Lingjuan Chen, Jiangxin Pu, Ping Liu* and Bin Dai
School of Chemistry and Chemical Engineering, Key Laboratory for Green Processing of Chemical Engineering of Xinjiang Bingtuan, Shihezi University,
Shihezi City, Xinjiang 832004, P.R. China
A series of bis-arylsulfenylated indoles (10), benzofurans (3), and benzothiophenes (3) and of monosulfenylated indoles (5), 12 of which
are novel, were prepared in good yields via a Cu-catalysed direct sulfenylation of benzoheterocycles with arylsulfonyl hydrazides.
Sulfonothioates are probably the major thiolated intermediates in this transformation.
Keywords: indoles, benzofurans, benzo[b]thiphenes, arylsulfonyl hydrazide, Cu-catalysed disulfenylation
The heterocyclic arylsulfide moiety is a useful building block
in medicinal chemistry. It is widely present in biologically
active compounds, natural products, pharmaceuticals and
organic materials.1–4 In addition to their potential synthetic
value and varying remarkable bioactivities, heterocyclic
arylsulfides are useful intermediates in organic syntheses.5
Several approaches have been reported for the preparation of
heterocyclic arylsulfides, such as the direct mono-thiolation
of heterocyclic arenes with arylsulfenyl halides,6 diaryl
disulfides,7,8 sodium sulfinates,9,10 arylsulfinic acids,11 aryl
thiols,12,13 aryl-N-thioimides,14–16 and sulfonyl hydrazides17–20 as
sources of the sulfurisation agents. For example, regioselective
mono-sulfenylations of indoles with sulfonyl hydrazides in the
presence of iodine or a DBU-based ionic liquid as catalyst gave
structurally diverse indole thioethers.17,19 A copper-catalysed
regioselective sulfenylation of indoles or pyrrolo[2,3-b]
pyridines with arylsulfonyl chlorides was also achieved by using
PPh3 as reductant.21 In addition, aryl benzofuran thioethers were
synthesised by the I2-catalysed cross-coupling of benzofurans
with aryl sulfonyl hydrazides.22
Although many methods have been successfully used to
construct structurally diverse heterocyclic mono-arylsulfides,
synthesis of heterocyclic bis-arylsulfides has not been well
documented. As early as 1992, the synthesis of 2,3-bis-sulfenyl
indoles was achieved by the reaction of indoles and aryl
sulfenyl chlorides.23–25 Subsequently, I2-mediated mono- and
disulfenylation reactions of indoles at the 2- and 3-positions
were reported and also various sulfurisation agents such as
diaryl disulfides, thiols and sodium sulfinates were used to
prepare 2,3-bis-sulfenyl indoles.13,26,27 Recently, a CuI-catalysed
regioselective sulfenylation of indoles with disulfides was
developed.28 Here we describe a novel Cu-catalysed direct bis-
sulfenylation of indoles, benzofurans and benzothiophenes with
arylsulfonyl hydrazides.
solvent in the presence of HOAc using Cu(OTf)2 as a copper
source (Scheme 1). Gratifyingly, this led to the formation of
2,3-bis(p-tolylthio)-1H-indole (3a; X = N) in 60% yield as a
single product (Table 1, entry 1). We then used this reaction
to optimise the reaction conditions and the results are shown
in Table 1. Other copper sources such as CuBr, CuI, Cu(TFA)2
and Cu(OAc)2, gave low yields of the desired product 3a (Table
1, entries 2–5). The reaction did not proceed in the absence
of copper (Table 1, entry 6). When we replaced DCE with
toluene, a nonpolar solvent, a 57% yield of the desired product
Table 1 Optimisation of the reaction conditions (catalyst, solvent) for
the 2,3-disulfenylation of indole (2; X = N) using tosylhydrazide (1a; Ar =
4-Me-C6H4) (Scheme 1)a
Catalyst
(mmol)
Solvent
(mL)
H2O
(mL)
HOAc
(mL)
Yield
Entry
(%)b
1
2
3
4
5
6
7
8
Cu(OTf)2 (0.2)
CuBr (0.2)
CuI (0.2)
Cu(TFA)2 (0.2)
Cu(OAc)2 (0.2)
–
Cu(OTf)2 (0.2)
Cu(OTf)2 (0.2)
Cu(OTf)2 (0.2)
Cu(OTf)2 (0.2)
Cu(OTf)2 (0.2)
Cu(OTf)2 (0.2)
Cu(OTf)2 (0.2)
Cu(OTf)2 (0.3)
Cu(OTf)2 (0.2)
Cu(OTf)2 (0.2)
Cu(OTf)2 (0.2)
DCE (2)
DCE (2)
DCE (2)
DCE (2)
DCE (2)
DCE (2)
Toluene (2)
DMSO (2)
Dioxane (2)
MeOH (2)
CH3CN (2)
DCE (2)
DCE (2)
DCE (2)
DCE(2)
DCE(1)
–
–
–
–
–
–
–
–
–
–
–
–
0.1
0.1
0.1
0.1
0.1
1
1
1
1
1
1
1
1
1
1
1
1
1
2
2
2
2
60
15
Trace
Trace
13
0
57
Trace
48
34
27
58
66
53
77
77
82
9
10
11
12c
13
14
15d
16d
17d
Toluene (1)
aReaction conditions: a mixture of tosylhydrazide (1a; Ar = 4-Me-C6H4) (0.8 mmol), indole
(2; X = N) (0.3 mmol), a Cu(ii) source (0.2 mmol), solvent (1 mL), HOAc (1 or 2 mL) and
Results and discussion
(sometimes) H2O (0.1 mL) was stirred under air at 80 °C for 8 h.
bIsolated yield.
The initial conditions we tried for the bis-thiolation of
1H-indole (2a; X = N) by p-toluenesulfonyl hydrazide (1a; Ar
= tosyl) was refluxing at 80 °C in 1,2-dichloroethane (DCE) as
c1a:2a = 0.6 mmol:0.3 mmol.
dAt 110 ºC.
Scheme 1
* Correspondent. E-mail: liuping1979112@aliyun.com

JOURNAL OF CHEMICAL RESEARCH 2018 457
was obtained (Table 1, entry 7). Polar solvents such as DMSO,
1,4-dioxane, methanol and acetonitrile resulted in lower yields
of the product (Table 1, entries 8–11). Next, these studies were
carried out at temperatures ranging from 80 °C to 110 °C using
different amounts of Cu(OTf)2, DCE, or toluene/H2O, and
HOAc (Table 1, entries 12–17). On the basis of these results,
the optimum conditions were: stirring a mixture of Cu(OTf)2
(0.2 mmol), toluene (1 mL), H2O (0.1 mL) and HOAc (2 mL) at
110 °C for 8 h.
With the optimal reaction conditions in hand, we next
examined the scope and limitations of the reaction. As
shown in Table 2, benzenesulfonohydrazide (1b; Ar = Ph)
underwent the thioether reaction to give a 59% yield of bis-
thioether product (3b; Ar = Ph). Benzenesulfonohydrazides
bearing electron-withdrawing functional groups at the para
and meta positions (1c–g; Ar = various) also afforded bis-
thioether products (3c–g; Ar = various) in 47–61% yields,
as did the substrates with electron-donating groups such as
4-(t-butyl)benzenesulfonohydrazide (1h; Ar = 4-But-C6H4)
and 4-methoxybenzenesulfonohydrazide (1i; Ar = 4-MeO-
C6H4), which gave the corresponding bis-thioether products 3h
(Ar = 4-But-C6H4) and 3i (Ar = 4-MeO-C6H4) in 58% and the
surprisingly low 14% yield, respectively.
Variously substituted indole derivatives were investigated
as coupling partners for this transformation (Scheme 2
and Table 3). The position and electronic properties of the
substituent groups have a very significant effect on the result
of the reaction under the standard conditions. For example,
1-methyl-1H-indole (4; R = H, R′ = Me) afforded a bis-thioether
product (5a; R = H, R′ = Me, n = 2) in 70% yield. However,
when 2-methyl-1H-indole (4; R = 2-Me, R′ = H) was reacted,
sulfenylation took place at the C3 position of the indole ring to
give the product (5b; R = 2-Me, R′ = H; n = 1) in 39% yield and
3-methyl-1H-indole (4; R = 3-Me, R′ = H) gave the 2-thiolated
product (5c; R = 2-Me, R′ = H; n = 1) in 24% yield. For three
1H-indoles with strong electron-withdrawing substituents, such
as –NO2, and –CN in the aromatic ring (4; R = 7-NO2, 5-NO2,
4-CN, R′ = H), only mono-thioether products at the C3 position
of the indole ring were obtained (5d–f; R = 7-NO2, 5-NO2,
4-CN , R′ = H; n = 1), and bis-thioether products were not
detected.
Benzofuran (2; X = O) and benzothiophene (2; X = S)
also suffered bis-thiolation with 4-substituted arylsulfonyl
hydrazides (1; Ar = 4-Me-C6H4, 4-MeO-C6H4, 4-But-C6H4,
4-F-C6H4), proceeding with 35–87% yields to furnish the
corresponding heterocycles (3j–p; X = O or S; Ar = 4-Me-C6H4,
4-MeO-C6H4, 4-But-C6H4, 4-F-C6H4) (Table 4). The electronic
effects of the substituents had no noticeable effect on the yields
of the reactions.
Table 2 Yields of a series of 2,3-bis(arylthio)-1H-indoles (3b–i; X = N;
Ar = various) prepared from the reaction of an arylhydrazide (1; Ar =
various) with indole (2; X = N) in the presence of Cu(ii) triflate (Scheme 1)a
To gain further insight into the mechanism, a series of control
experiments were performed (Scheme 3). When one equivalent
of 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) as a radical
scavenger was added to the reaction mixture of TsNHNH2 and
1H-indole, the yield was decreased to 40%. Hydroquinone
replacement of TEMPO completely inhibited the formation
of thioether 3a (Scheme 3, [1]). These results suggested that
possibly both sulfur radicals (Tol-S•) and sulfonyl radicals
(Tol-SO2•) were generated through decomposition of TsNHNH2
during the sulfenylation reaction. When only TsNHNH2 as
Entry
Product 3
Ar/1
C6H5–/1b
Yield (%)b
1
2
3
4
5
6
7
8
3b
3c
3d
3e
3f
3g
3h
3i
59
61
50
56
55
47
58
14
4-Cl-C6H4–/1c
4-F-C6H4–/1d
3-F-C6H4–/1e
4-CF3O-C6H4–/1f
4-CF3-C6H4–/1g
4-tBu-C6H4–/1h
4-MeO-C6H4–/1i
aReaction conditions: a mixture of an arylhydrazide (1; Ar = various) (0.8 mmol), indole
(2; X = N) (0.3 mmol), Cu(OTf)2 (0.2 mmol), toluene (1 mL), HOAc (2 mL) and H2O (0.1 mL)
was stirred at 110 °C for 8 h.
Table 4 Yields of a series of 2,3-(diarylthio)-benzofurans (3j–l; X = O;
Ar = various) and 2,3-(diarylthio)-benzo[b]thiophenes (3m–p; X = S;
Ar = various) prepared from the reaction of an arylhydrazide (1; Ar =
various) with benzofuran (2; X = O) or benzo[b]thiophene (2; X = S) in the
presence of Cu(ii) triflate (Scheme 1)a
bIsolated yield.
Table 3 Yields of a series of 2- or 3-(tolylthio)-1H-indoles (5a–f; R, R′ =
various) prepared from the reaction of tosylhydrazide (1a) with variously
substituted indoles (4; R, R′ = various) in the presence of Cu(ii) triflate
(Scheme 2)a
Entry
Product 3
3j
X
O
O
O
S
S
S
S
Ar
Yield (%)b
1
2
3
4
5
6
7
4-Me-C6H4–
4-MeO-C6H4–
4-tBu-C6H4–
4-Me-C6H4–
4-MeO-C6H4–
4-tBu-C6H4–
4-F-C6H4–
60 (trace)c
3k
3l
3m
3n
3o
3p
55
35
54
39
87
52
Entry
Product 5
R
H
n
2
1
1
1
1
1
Yield (%)b
R′
Me
H
H
H
1
2
3
4
5
6
5a
5b
5c
5d
5e
5f
70
39
24
82
59
41
2-Me
3-Me
7-NO2
5-NO2
7-CN
H
H
aReaction conditions: a mixture of an arylhydrazide (1; Ar = various) (0.8 mmol),
benzofuran (2; X = O) or benzo[b]thiophene (2; X = S) (0.3 mmol), Cu(OTf)2 (0.2 mmol),
DCE (2 mL), HOAc (2 mL) and H2O (0.1 mL) was stirred at 110 °C for 8 h.
bIsolated yields.
aReaction conditions: a mixture of tosylhydrazide (1a) (0.8 mmol), variously substituted
indoles (4; R, R′ = various) (0.3 mmol), Cu(OTf)2 (0.2 mmol), toluene (1 mL), HOAc (2 mL)
and H2O (0.1 mL) was stirred at 110 °C for 8 h.
cToluene (2 mL) as solvent. Only a trace of product with DCE.
bIsolated yields.
Scheme 2

458 JOURNAL OF CHEMICAL RESEARCH 2018
substrate was used, S-p-tolyl-4-methylbenzenesulfonothioate
(3ab) and 1,2-di-p-tolyldisulfane (3aa) were obtained in
a ratio of 2:1 under the standard conditions (Scheme 3, [2]).
If 1H-indole was added to the above reaction mixture, bis-
thioether product 3a was formed in 10% yield (Scheme 3, [3]).
Therefore, we can speculate that intermediates 3aa or 3ab, or
both, play an important role in the thioetherification.
To further identify the active intermediates of the reaction,
different sulfur sources were investigated (Scheme 4). When
3aa was used as thioether reagent under the standard conditions,
Scheme 3
Tol
S
+
[1]
[2]
Standard conditions
Tol
S
no reaction
N
H
3aa,
0.4 mmol
2a,
2a,
0.3 mmol
Tol
S
O
Tol
Standard conditions
+
Tol
S S
O
S
N
H
N
H
Tol
3ab,
0.3 mmol
0.4 mmol
3a,
31%
Tol
S
Standard conditions
TBHP (1.2 equiv.)
Tol
S
+
[3]
S
Tol
S
N
H
N
Tol
H
3aa,
0.4 mmol
2a,
0.3 mmol
3a,
30%
OMe
OMe
S
Tol
N
H
S
S
+
2a,
Tol
0.3 mmol
+
Standard
OMe
conditions
N
H
[4]
S
N
O
S
H 8%
3i,
S
10%
OMe
O
O
S
O
S
S
+
Tol
S
3ac,
0.4 mmol
Tol
Tol
O
O
OMe
3aa
, 8%
3ac
, 60%
Scheme 4

JOURNAL OF CHEMICAL RESEARCH 2018 459
the bis-thioether product 3a was not detected (Scheme 4, [1]). In
contrast, the reaction of 2a with 3ab as a sulfur source proceeded
smoothly to give a 31% yield of 3a (Scheme 4, [2]). Moreover,
the reaction with 2a and 3aa in the presence of tetrabutyl
hydroperoxide (TBHP) also afforded the desired product 3a in
30% yield (Scheme 4, [3]). As THBP converts 3aa into 3ab,
we speculated that intermediate 3ab plays an important role
in the thioetherification. The reaction of (4-methoxyphenyl)
4-methylbenzenesulfonothioate 3ac as a sulfur source with
indole (2a) was tested under the standard conditions, and
the bis-thioether products 2,3-bis((4-methoxyphenyl)thio)-
1H-indole (3i, 10%) and 2-((4-methoxyphenyl)thio)-3-(p-
tolylthio)-1H-indole (8%) were obtained, accompanied by an
8% yield of the product 3ab and recovery of unchanged 3ac
(60%) (Scheme 4, [4]).
(2a) was 1:1, we still obtained the bis-sulfenylated product
(3f), and the mono-sulfide was not detected. In addition,
we found that the reaction of 3-(p-tolylthio)-1H-indole as
substrate and 4-methoxybenzenesulfonohydrazide did not give
product 2-((4-methoxyphenyl)thio)-3-(p-tolylthio)-1H-indole
(Scheme 5).
According to the above results of control experiments, a
plausible mechanism catalysed by Cu(OTf)2 is proposed in
Scheme 6. First, TsNHNH2 (1) is oxidised to intermediate
(I) in the presence of Cu(OTf)2, and then intermediate (I) is
oxidised to generate sulfonyl radicals (II). Some of the sulfonyl
radicals are subsequently reduced to arylthio radicals (III) by
monovalent copper ions. Then, the aryl sulfonyl radical (II)
interacts with the arylthio radical (III) to yield two important
thioether intermediates 4a and 4b, respectively. The following
catalytic cycle is proposed: 1H-indole (2a) reacts with
monovalent copper to produce a 1H-indole(C3) monovalent-
copper intermediate (IV), which reacts with 4b to form the
intermediate (V). After eliminating arylsulfurous acid to give
In previous reports13–16, it was mentioned that mono- or di-
sulfenylated products can be selectively obtained by changing
the amount of sulfonylhydrazine. However, when the ratio of
4-(trifluoromethoxy)benzenesulfonohydrazide and indole
OCF3
S
O
Standard
+
NHNH2
conditions
F
3CO
S
S
N
H
N
H
O
1f,
2a,
0.3 mmol
0.3 mmol
3f,
28%
Tol
OCF3
S
Tol
S
Standard
conditions
O
S
+
MeO
S NHNH2
O
N
N
H
H
no reaction
0.36 mmol
0.3 mmol
OMe
Scheme 5
air
air
Cu+
Cu2+
-N2
Cu+
Cu+
Cu2+
Cu2+
R-S
R-SO2
(II)
NHNH2
RSO2
N=NH
RSO2
(III)
1
(I)
+
+
RSO2-SR
R-S
(III)
R-S
(III)
RS-SR R-SO2
4a
(II)
R-S
(III)
RSO2-SR RS-SR
4b 4a
partial
conversion
4b
RS
Cu
SR
Cu
R
SO2
Cu
CuX
(X = OTf or OAc)
-HX
RSO2-SR
HX
-RSO2H
N
N
N
N
H
H
H
H
2a
(IV)
(V)
(VI)
CuX
HX
SR
SR
Cu
SR
SR
-CuX
-RSO2H
SR
Cu
SO2
RSO2-SR
HX
N
N
R
N
H
H
H
3
(VII)
(VIII)
Scheme 6

460 JOURNAL OF CHEMICAL RESEARCH 2018
(d, J = 249.4 Hz), 161.3 (d, J = 245.5 Hz), 137.0, 133.9, 133.0 (d,
J = 3.4 Hz), 132.5 (d, J = 8.5 Hz), 130.0, 129.2 (d, J = 3.5 Hz), 128.9
(d, J = 8.0 Hz), 124.2, 121.5, 119.9, 116.7 (d, J = 22.3 Hz), 115.9 (d,
J = 22.2 Hz), 111.3, 109.6.
the intermediate (VI), followed by its reductive elimination to
give a mono-sulfenylated 1H-indole(C3) copper(I) intermediate
(VII). Subsequently, intermediate (VII) undergoes an
oxidative addition reaction with 4b to give intermediate (VIII),
which suffers reductive elimination to give a bis-sulfenylated
1H-indole (3), while the monovalent-Cu catalyst is released and
ready for use in the next catalytic cycle.
2,3-Bis((3-fluorophenyl)thio)-1H-indole (3e): Light yellow solid;
yield 62 mg (56%); m.p. 97.7–101.2 °C; 1H NMR (400 MHz, CDCl3):
δ 8.49 (s, 1H), 7.60 (d, J = 8.0 Hz, 1H), 7.40 (d, J = 8.4 Hz, 1H),
7.34–7.29 (m, 1H), 7.24–7.20 (m, 1H), 7.17 (d, J = 8.8 Hz, 1H), 7.10 (td,
J = 4.0, 4.0 Hz, 1H), 6.98 (dt, J = 1.2, 1.2 Hz, 1H), 6.88 (dd, J = 1.2,
1.2 Hz, 3H), 6.80–6.72 (m, 1H), 6.72–6.67 (m, 1H); 13C NMR (101
MHz, CDCl3): δ 163.12 (d, J = 247.7 Hz), 163.08 (d, J = 249.6 Hz),
140.6 (d, J = 7.5 Hz), 137.1 (d, J = 7.6 Hz), 132.3, 130.7 (d, J = 8.4 Hz),
130.1 (d, J = 8.5 Hz), 129.9, 124.6, 124.5 (d, J = 3.1 Hz), 122.1 (d,
J = 2.9 Hz), 121.8, 120.1, 115.9 (d, J = 23.7 Hz), 114.2 (d, J = 21.3 Hz),
113.4 (d, J = 24.0 Hz), 112.2 (d, J = 21.5 Hz), 111.6, 110.0. HRMS (EI)
m/z calcd for C20H13F2NS2 [M]: 369.0457; found: 369.0444.
Conclusions
In summary, we have proposed an efficient Cu-catalysed bis-
thiolation of indoles, benzofurans and benzo[b]thiophenes with
arylsulfonyl hydrazides. This system features environmental
friendliness, wide substrate scope and good functional group
tolerance. Experimental analysis suggests that both free-
radical formation and a Cu-catalysed cycle may be involved
in the reaction pathway, and the sulfonothioates are the main
thiolation intermediates in this transformation.
2,3-Bis((4-(trifluoromethoxy)phenyl)thio)-1H-indole (3f): Light
1
yellow oil; yield 83 mg (55%); H NMR (400 MHz, CDCl3): δ 8.45
(s, 1H), 7.60 (d, J = 8.0 Hz, 1H), 7.37 (d, J = 8.0 Hz, 1H), 7.32–7.27
(m, 1H), 7.24–7.17 (m, 3H), 7.06 (td, J = 4.4, 4.2 Hz, 4H), 6.98 (d,
J = 8.8 Hz, 2H); 13C NMR (101 MHz, CDCl3): δ 148.5 (d, J = 2.0 Hz),
147.1 (d, J = 2.0 Hz), 137.0, 136.8, 133.3, 132.8, 130.8, 129.9, 127.9,
124.6, 121.97, 121.96, 121.8, 121.6, 120.1, 111.6, 110.1. HRMS (EI) m/z
calcd for C22H13F6NO2S2 [M]: 501.0292; found: 501.0279.
2,3-Bis((4-(trifluoromethyl)phenyl)thio)-1H-indole (3g): Light
yellow oil; yield 66 mg (47%); 1H NMR (400 MHz, CDCl3): δ 8.60 (s,
1H), 7.59 (d, J = 8.0 Hz, 1H), 7.42 (dd, J = 3.6, 3.2 Hz, 3H), 7.37–7.33
(m, 3H), 7.24–7.17 (m, 3H), 7.09 (d, J = 8.4 Hz, 2H); 13C NMR
(101 MHz, CDCl3): δ 143.1 (d, J = 1.5 Hz), 140.2 (d, J = 1.6 Hz), 137.2,
131.4, 129.8, 128.1, 126.3, 126.24, 126.2, 126.0, 125.7, 125.7, 125.65,
125.0, 122.0, 120.2, 111.8, 110.2. HRMS (EI) m/z calcd for C22H13F6NS2
[M]: 469.0394; found: 469.0374.
2,3-Bis((4-(t-butyl)phenyl)thio)-1H-indole (3h): Light yellow solid;
yield 78 mg (58%); m.p. 131.5–133.5 °C; 1H NMR (400 MHz, CDCl3):
δ 8.23 (s, 1H), 7.60 (d, J = 7.6 Hz, 1H), 7.30 (d, J = 2.0 Hz, 1H), 7.29
(d, J = 2.0 Hz, 2H), 7.26 (s, 1H), 7.25–7.20 (m, 2H), 7.20–7.16 (m, 2H),
7.16–7.12 (m, 1H), 7.08 (d, J = 8.4 Hz, 2H), 1.29 (s, 9H), 1.25 (s, 9H);
13C NMR (101 MHz, CDCl3): δ 151.1, 148.3, 136.9, 134.8, 130.5, 130.4,
130.3, 126.7, 126.67, 125.9, 123.6, 121.2, 120.0, 111.1, 108.6, 34.7, 34.5,
31.5, 31.4. HRMS (EI) m/z calcd for C28H31NS2 [M]: 445.1898; found:
445.1884.
Experimental
NMR spectra were obtained on a Bruker DPX-400 spectrometer
(1H NMR at 400 Hz, 13C NMR at 100 Hz) in CDCl3 using TMS as an
internal standard. Chemical shifts (δ) are given in ppm and coupling
constants (J) are given in Hz. EI mass spectra were measured on a
LC/Q–TOF MS (Micromass, England). All products were isolated by
short chromatography on a silica gel (200–300 mesh) column using
petroleum ether (PE) (60–90 °C); unless otherwise noted 1H-indoles
and its derivatives, arylsulfonyl hydrazides, Cu(OTf)2 and solvents of
analytical grade were purchased from Adamas-beta Pharmaceuticals,
Inc.
Direct thiolation of benzoheterocycles with arylsulfonyl hydrazides;
general procedure
First, a solution of a benzoheterocycle (an indole, a benzofuran or a
benzo[b]thiophene) (0.3 mmol), an arylsulfonyl hydrazide (0.8 mmol),
Cu(OTf)2 (0.2 mmol), HOAc (2 mL) and H2O (0.1 mL) in toluene
(1 mL) was stirred at 110 °C for 8 h under air. Second, the reaction
mixture was quenched with water (10 mL) and extracted with EtOAc
(3 × 10 mL). The combined EtOAc extracts were dried over anhydrous
MgSO4 and the solvent removed under reduced pressure. The residue
was purified by flash column chromatography on silica gel using PE/
EtOAc as the eluent.
2,3-Bis(p-tolylthio)-1H-indole (3a)13: Light yellow oil; yield 89 mg
(82%); 1H NMR (400 MHz, CDCl3): δ 8.20 (s, 1H), 7.57 (d, J = 8.0 Hz,
1H), 7.28 (d, J = 8.0 Hz, 1H), 7.25–7.19 (m, 3H), 7.15–7.11 (m, 1H),
7.08 (d, J = 8.0 Hz, 2H), 7.04 (d, J = 8.0 Hz, 2H), 6.96 (d, J = 8.0 Hz,
2H), 2.32 (s, 3H), 2.25 (s, 3H); 13C NMR (101 MHz, CDCl3): δ 137.9,
136.9, 135.0, 134.8, 134.6, 130.9, 130.4, 130.3, 130.2, 129.6, 127.1,
123.6, 121.2, 119.8, 111.1, 108.4, 21.2, 21.1.
2,3-Bis(phenylthio)-1H-indole (3b)29: White solid; yield 59 mg
(59%); m.p. 87.8–88.8 °C (lit.29 m.p. 96–98 °C); 1H NMR (400 MHz,
CDCl3): δ 8.33 (s, 1H), 7.58 (d, J = 7.6 Hz, 1H), 7.32 (d, J = 8.0 Hz,
1H), 7.27 (dd, J = 2.4, 1.2 Hz, 3H), 7.25–7.19 (m, 3H), 7.16 (dd, J = 0.8,
1.6 Hz, 2H), 7.13–7.09 (m, 3H), 7.08–7.03 (m, 1H); 13C NMR (101
MHz, CDCl3): δ 138.2, 137.0, 134.4, 133.7, 130.1, 129.8, 129.5, 128.8,
127.4, 126.7, 125.2, 124.0, 121.3, 120.0, 111.3, 109.3.
2,3-Bis((4-methoxyphenyl)thio)-1H-indole (3i)31: Light yellow
solid; yield 17 mg (14%); m.p. 142.3–143.7 °C (lit.31 m.p. 134–137 °C);
1H NMR (400 MHz, CDCl3): δ 8.10 (s, 1H), 7.58 (d, J = 8.0 Hz, 1H),
7.35 (d, J = 8.8 Hz, 2H), 7.24 (s, 1H), 7.19 (dd, J = 1.2, 1.2 Hz, 1H),
7.16–7.10 (m, 3H), 6.83 (d, J = 8.8 Hz, 2H), 6.72 (d, J = 8.8 Hz, 2H),
3.79 (s, 3H), 3.73 (s, 3H); 13C NMR (101 MHz, CDCl3): δ 160.0, 158.1,
138.5, 136.7, 135.8, 133.9, 130.4, 130.1, 129.4, 123.3, 121.1, 119.6, 115.3,
114.6, 110.9, 55.6, 29.9.
2,3-Bis(p-tolylthio)benzofuran (3j)32: Colourless oil; yield 65 mg
1
(60%); H NMR (400 MHz, CDCl3): δ 7.42 (d, J = 8.4 Hz, 1H), 7.36
(d, J = 7.6 Hz, 1H), 7.31 (d, J = 8.4 Hz, 2H), 7.29–7.22 (m, 1H), 7.18
(d, J = 7.6 Hz, 1H), 7.13 (d, J = 8.4 Hz, 2H), 7.08 (d, J = 8.0 Hz, 2H),
7.00 (d, J = 8.0 Hz, 2H), 2.30 (s, 3H), 2.27 (s, 3H); 13C NMR (101 MHz,
CDCl3): δ 156.1, 153.2, 138.1, 136.3, 131.8, 131.3, 130.2, 129.9, 129.4,
129.2, 128.6, 125.7, 123.5, 120.6, 116.5, 111.7, 21.3, 21.1.
2,3-Bis((4-chlorophenyl)thio)-1H-indole (3c)30: Light yellow oil;
yield 74 mg (61%); 1H NMR (400 MHz, CDCl3): δ 8.41 (s, 1H), 7.56 (d,
J = 8.0 Hz, 1H), 7.35 (d, J = 8.0 Hz, 1H), 7.28 (t, J = 7.6 Hz, 1H), 7.19
(s, 1H), 7.17 (s, 2H), 7.13 (d, J = 8.4 Hz, 2H), 7.09 (d, J = 8.4 Hz, 2H),
6.98 (d, J = 9.6 Hz, 2H); 13C NMR (101 MHz, CDCl3): δ 137.0, 136.6,
133.6, 132.99, 132.95, 131.2, 130.8, 129.9, 129.6, 129.0, 128.0, 124.4,
121.7, 120.0, 111.5, 109.7.
2,3-Bis((4-fluorophenyl)thio)-1H-indole (3d)13: Light yellow
oil; yield 55 mg (50%); 1H NMR (400 MHz, CDCl3): δ 8.32 (s,
1H), 7.57 (d, J = 8.0 Hz, 1H), 7.32 (d, J = 8.0 Hz, 1H), 7.29–7.24
(m, 3H), 7.19–7.14 (m, 1H), 7.11–7.06 (m, 2H), 6.94 (t, J = 8.8 Hz,
2H), 6.85 (t, J = 8.8 Hz, 2H); 13C NMR (101 MHz, CDCl3): δ 162.5
2,3-Bis((4-methoxyphenyl)thio)benzofuran (3k): Light yellow oil;
yield 65 mg (55%); 1H NMR (400 MHz, CDCl3): δ 7.43 (d, J = 8.8 Hz,
2H), 7.39 (d, J = 8.4 Hz, 1H), 7.35 (d, J = 8.0 Hz, 1H), 7.27 (dd, J = 1.6,
1.2 Hz, 1H), 7.23 (d, J = 8.8 Hz, 2H), 7.16 (t, J = 15.2 Hz, 1H), 6.82
(d, J = 8.8 Hz, 2H), 6.76 (d, J = 8.8 Hz, 2H), 3.77 (s, 3H), 3.74 (s, 3H);
13C NMR (101 MHz, CDCl3): δ 160.0, 158.8, 155.9, 153.4, 133.9, 131.2,
129.4, 125.8, 125.5, 123.5, 122.9, 120.4, 116.5, 115.0, 114.8, 111.6, 55.5,
55.4. HRMS (EI) m/z calcd for C22H18O3S2 [M]: 394.0694; found:
394.0678.
2,3-Bis((4-(t-butyl)phenyl)thio)benzofuran (3l): Light yellow oil;
yield 47 mg (35%); 1H NMR (400 MHz, CDCl3): δ 7.42 (t, J = 9.0 Hz,
2H), 7.34 (d, J = 8.8 Hz, 2H), 7.33–7.25 (m, 4H), 7.23 (d, J = 4.8 Hz,

JOURNAL OF CHEMICAL RESEARCH 2018 461
1H), 7.20 (d, J = 8.0 Hz, 2H), 7.15 (d, J = 8.8 Hz, 2H), 1.28 (s, 9H),
1.26 (s, 9H); 13C NMR (101 MHz, CDCl3): δ 156.1, 153.4, 151.2, 149.5,
132.0, 130.9, 129.5, 129.4, 128.2, 126.5, 126.2, 125.7, 123.6, 120.7,
116.7, 111.7, 34.7, 34.6, 31.4, 31.37. HRMS (EI) m/z calcd for C28H30OS2
[M]: 446.1738; found: 446.1722.
2,3-Bis(p-tolylthio)benzo[b]thiophene (3m): White solid; yield 61
mg (54%); m.p. 75.3–78.1 °C; 1H NMR (400 MHz, CDCl3): δ 7.72 (d,
J = 7.2 Hz, 1H), 7.63 (d, J = 7.2 Hz, 1H), 7.43 (d, J = 8.0 Hz, 2H), 7.29
(m, 1H), 7.25 (d, J = 6.0 Hz, 1H), 7.16 (d, J = 8.0 Hz, 2H), 7.06 (d,
J = 8.4 Hz, 2H), 7.00 (d, J = 8.0 Hz, 2H), 2.36 (s, 3H), 2.26 (s, 3H);
13C NMR (101 MHz, CDCl3): δ 147.1, 140.6, 139.5, 139.3, 135.7, 133.3,
132.8, 130.3, 130.0, 129.9, 127.7, 125.1, 124.8, 123.03, 123.0, 122.0,
21.4, 21.1. HRMS (EI) m/z calcd for C22H18S3 [M]: 378.0571; found:
378.0554.
135.5, 134.4, 130.5, 129.6, 125.9, 122.2, 120.8, 119.1, 110.7, 100.0, 21.0,
12.3.
3-Methyl-2-(p-tolylthio)-1H-indole (5c)35: White solid; yield 18 mg
(24%); m.p. 100.1–100.6 °C (lit.35 m.p. 93–95 °C); 1H NMR (400 MHz,
CDCl3): δ 7.89 (s, 1H), 7.59 (t, J = 7.0 Hz, 1H), 7.29–7.21 (m, 2H),
7.15–7.11 (m, 1H), 7.05–6.97 (m, 4H), 2.40 (d, J = 6.8 Hz, 3H), 2.27
(d, J = 6.0 Hz, 3H); 13C NMR (101 MHz, CDCl3) δ 136.9, 135.9, 133.4,
130.0, 128.6, 127.2, 123.5, 122.4, 119.7, 119.5, 119.4, 110.9, 21.0, 9.6.
7-Nitro-3-(p-tolylthio)-1H-indole (5d): Yellow solid; yield 70 mg
1
(82%); m.p. 177.2–179.7 °C; H NMR (400 MHz, CDCl3): δ 10.09
(s, 1H), 8.21 (d, J = 8.8 Hz, 1H), 7.95 (d, J = 8.0 Hz, 1H), 7.67 (d,
J = 2.4 Hz, 1H), 7.23 (d, J = 8.0 Hz, 1H), 7.04 (d, J = 8.4 Hz, 2H), 7.00
(d, J = 8.4 Hz, 2H), 2.26 (s, 3H); 13C NMR (101 MHz, CDCl3): δ 135.6,
134.3, 133.6, 132.7, 132.5, 130.1, 129.8, 128.0, 127.0, 120.4, 120.3,
106.6, 21.0. HRMS (EI) m/z calcd for C15H12N2O2S [M]: 284.0619;
found: 284.0609.
2,3-Bis((4-methoxyphenyl)thio)benzo[b]thiophene (3n): White
1
solid; yield 48 mg (39%); m.p. 127.2–127.9 °C; H NMR (400 MHz,
CDCl3): δ 7.73 (d, J = 8.0 Hz, 1H), 7.60 (d, J =8.0 Hz, 1H), 7.52 (d, J
= 8.8 Hz, 2H), 7.29 (t, J = 7.6 Hz, 1H), 7.24 (m, 1H), 7.19 (d, J = 8.8
Hz, 2H), 6.90 (d, J = 8.8 Hz, 2H), 6.76 (d, J = 8.8 Hz, 2H), 3.82 (s,
3H), 3.73 (s, 3H); 13C NMR (101 MHz, CDCl3): δ 160.8, 158.5, 148.4,
140.8, 139.1, 136.0, 130.2, 126.8, 125.1, 124.4, 123.5, 122.6, 122.2,
121.9, 115.2, 114.8, 55.5, 55.4. HRMS (EI) m/z calcd for C22H18O2S3
[M]: 410.0469; found: 410.0446.
5-Nitro-3-(p-tolylthio)-1H-indole (5e)31: Yellow solid; yield
1
50 mg (59%); m.p. 169.6–171.2 °C (lit.31 m.p. 204–207 °C); H NMR
(400 MHz, CDCl3): δ 8.80 (s, 1H), 8.57 (d, J = 2.0 Hz, 1H), 8.16 (dd,
J = 9.0, 2.2 Hz, 1H), 7.63 (d, J = 2.4 Hz, 1H), 7.48 (d, J = 9.0 Hz,
1H), 7.06 (d, J = 8.4 Hz, 2H), 7.01 (d, J = 8.2 Hz, 2H), 2.26 (s, 3H);
13C NMR (101 MHz, CDCl3): δ 136.9, 135.4, 134.0, 129.8, 128.3, 127.2,
122.7, 118.2, 116.7, 104.5, 103.2, 21.1.
2,3-Bis((4-(t-butyl)phenyl)thio)benzo[b]thiophene (3o): White
solid; yield 116 mg (87%); m.p. 104.6–107.3 °C; 1H NMR (400 MHz,
CDCl3): δ 7.75 (d, J = 9.2 Hz, 1H), 7.64 (d, J = 6.8 Hz, 1H), 7.45 (d,
J = 8.4 Hz, 2H), 7.35 (d, J = 8.4 Hz, 2H), 7.29 (m, 1H), 7.26 (m, 1H),
7.20 (d, J = 8.4 Hz, 2H), 7.08 (d, J = 8.4 Hz, 2H), 1.31 (s, 9H), 1.25 (s,
9H); 13C NMR (101 MHz, CDCl3): δ 152.2, 148.9, 146.9, 140.6, 139.6,
132.9, 132.8, 130.2, 127.3, 126.6, 126.2, 125.1, 124.8, 123.4, 123.1,
122.0, 34.8, 34.5, 31.41, 31.4. HRMS (EI) m/z calcd for C28H30S3 [M]:
462.1510; found: 462.1515.
3-(p-Tolylthio)-1H-indole-7-carbonitrile (5f): White solid; yield
33 mg (41%); m.p. 175.5–178.3 °C; H NMR (400 MHz, CDCl3): δ
8.78 (s, 1H), 7.68–7.62 (m, 2H), 7.52 (dd, J = 0.8, 0.8 Hz, 1H), 7.29 (d,
J = 8.0 Hz, 1H), 7.10 (d, J = 8.2 Hz, 2H), 7.00 (d, J = 8.0 Hz, 2H),
2.25 (s, 3H); 13C NMR (101 MHz, CDCl3): δ 136.9, 135.4, 135.4, 133.9,
129.8, 128.6, 128.3, 127.3, 122.7, 118.1, 116.6, 104.7, 103.3, 21.1. HRMS
(EI) m/z calcd for C16H12N2S [M]: 264.0721; found: 264.0710.
1
Acknowledgements
2,3-Bis((4-fluorophenyl)thio)benzo[b]thiophene (3p): White solid;
yield 60 mg (52%); m.p. 75.8–78.1 °C; H NMR (400 MHz, CDCl3):
We gratefully acknowledge financial support of this work
by the National Natural Science Foundation of China (No.
21563025), and the Program for Changjiang Scholars and
Innovative Research Team in University (No. IRT_15R46), and
Yangtze River Scholar Research Project of Shihezi University
(No. CJXZ201601).
1
δ 7.75–7.70 (m, 1H), 7.66 (dd, J = 2.0, 1.6 Hz, 1H), 7.50 (dd, J = 5.2,
5.2 Hz, 2H), 7.35–7.27 (m, 2H), 7.12 (dd, J = 5.2, 5.2 Hz, 2H), 7.04 (t,
J = 8.6 Hz, 2H), 6.89 (t, J = 8.6 Hz, 2H); 13C NMR (101 MHz, CDCl3):
δ 164.6, 162.8, 162.1, 160.3, 146.3, 140.3, 139.5, 135.33, 135.3, 131.22,
131.2, 129.7, 129.6, 128.7, 128.6, 125.4, 125.2, 123.7, 123.0, 122.2,
116.9, 116.7, 116.4, 116.2. HRMS (EI) m/z calcd for C20H12F2S3 [M]:
386.0069; found: 386.0054.
Electronic Supplementary Information
The ESI associated with this paper can be found at:
http://ingentaconnect.com/content/stl/jcr/2018/00000042/00000009/art00003
1,2-Di-p-tolyldisulfane (3aa)33: White solid; yield 24 mg (33%); m.p.
1
39–40 °C (lit.33 m.p. 39–40 °C); H NMR (400 MHz, CDCl3): δ 7.38
(d, J = 8.0 Hz, 4H), 7.10 (d, J = 8.0 Hz, 4H), 2.32 (s, 6H).
Received 11 July 2018; accepted 7 August 2018
Paper 1805520
https://doi.org/10.3184/174751918X15350179602459
Published online: 3 September 2018
S-(p-tolyl)-4-methylbenzenesulfonothioate (3ab)34: White solid;
yield 52 mg (62%); m.p. 76.0–76.8 °C (lit.34 m.p. 76.7–77.5 °C);
1H NMR (400 MHz, CDCl3): δ 7.46 (d, J = 8.4 Hz, 2H), 7.24 (d, J = 8.4
Hz, 2H), 7.21 (d, J = 8.0 Hz, 2H), 7.14 (d, J = 8.0 Hz, 2H), 2.42 (s, 3H),
2.38 (s, 3H).
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