One-pot synthesis of aryl alkyl thioethers and diaryl disulfides using carbon disulfide as a sulfur surrogate in the presence of diethylamine catalyzed by copper(I) iodide in polyethylene glycol (PEG200)

Article abstract of DOI:10.1016/j.tetlet.2014.01.001

A copper catalyzed one-pot protocol for the preparation of aryl alkyl thioethers and diaryl disulfides using carbon disulfide as the sulfur source and diethylamine in polyethylene glycol (PEG200) is described.

Full text of DOI:10.1016/j.tetlet.2014.01.001

Tetrahedron Letters 55 (2014) 1212–1217
Contents lists available at ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
One-pot synthesis of aryl alkyl thioethers and diaryl disulfides
using carbon disulfide as a sulfur surrogate in the presence of
diethylamine catalyzed by copper(I) iodide in polyethylene
glycol (PEG200)
⇑
⇑
Habib Firouzabadi , Nasser Iranpoor , Arash Samadi
The Late Professor Ali Akbar Moshfegh Laboratory, Chemistry Department, College of Sciences, Shiraz University, Shiraz 71454, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
A copper catalyzed one-pot protocol for the preparation of aryl alkyl thioethers and diaryl disulfides using
carbon disulfide as the sulfur source and diethylamine in polyethylene glycol (PEG200) is described.
Ó 2014 Elsevier Ltd. All rights reserved.
Received 15 August 2013
Revised 27 November 2013
Accepted 2 January 2014
Available online 9 January 2014
Keywords:
Thioether
Copper(I) iodide
Polyethylene glycol
Carbon disulfide
Diaryl disulfide
Aryl alkyl thioether moieties are found in many pharmaceuti-
cally and biologically active compounds. Numerous examples of
drugs applied for diabetes, Alzheimer’s and Parkinson’s diseases,
inflammatory and immune diseases have aryl sulfide moieties in
their structures.1 Thus protocols leading to C–S bond generation,
which are practical, cheap, and efficient have attracted a great deal
of attention.2 Cross-coupling reactions catalyzed by transition me-
tal catalysts are a tactic for C–S bond generation.3 The preparation
of thioethers by the reaction of thiols with aryl halides catalyzed by
transition metals such as palladium,4 nickel,5 cobalt,6 copper,7
indium,8 iron,9 and manganese salts10 have been reported. Some
of these studies have led to new and efficient methods, but the
majority of the reported reactions are conducted in harmful organ-
ic solvents. Disposal of organic solvents is a major problem for the
chemical industry. Furthermore, organic solvents are expensive,
toxic, and flammable. In contrast, polyethylene glycols (PEGs)
and their derivatives have negligible vapor pressures and are rec-
ognized to be inexpensive, thermally stable, recoverable, non-toxic
compounds which are suitable media for environmentally friendly
and safe chemical reactions.11 We have reported previously the
one-pot odorless C–S bond formation via Michael addition using
thiourea and alkyl bromides in water,12 in aqueous polyethylene
glycol or in ionic liquids.13 We have also applied this protocol for
the odorless thioarylation of alkyl bromides with aryl halides in
the presence of copper(I) iodide in wet PEG200.14
Moreover, after this report, some other sulfur surrogates such as
thioacetamide,15 thiourea,16 potassium thiocyanate,17 thioace-
tate,18 potassium ethyl xanthogenate,19 sodium hydrosulfide,20
and elemental sulfur21 were used for the conversion of aryl com-
pounds (mostly halides) into aryl thioethers by catalysis with Pd
or Cu.
The study of cross-coupling reactions of phenols due to their
nature as electrophilic coupling partners is a challenging topic.22
Most of the studied phenolic derivatives in carbon–sulfur bond for-
mation reactions are triflates. Regardless of the exceptional reac-
tivities of these compounds, triflates are materials with limited
stability.23 Therefore, other phenolic esters such as tosylates may
be better precursors for electrophilic coupling reactions. Recently,
a Letter in which a copper-catalyzed synthesis of diaryl thioethers
by the reaction of aryl iodides with carbon disulfide in the presence
of DBU was published.24 This publication prompted us to report
our preliminary findings in this area.
Herein, we report a one-pot synthesis of aryl alkyl thioethers
and diaryl disulfides using carbon disulfide as a sulfur substitute
in the presence of diethylamine catalyzed by copper(I) iodide in
polyethylene glycol (PEG200) as an eco-friendly solvent. Aryl
⇑
Corresponding authors. Tel.: +98 711 613 7110; fax: +98 711 646 0788.
E-mail addresses: firouzabadi@chem.susc.ac.ir (H. Firouzabadi), iranpoor@
chem.susc.ac.ir (N. Iranpoor).
0040-4039/$ - see front matter Ó 2014 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2014.01.001

H. Firouzabadi et al. / Tetrahedron Letters 55 (2014) 1212–1217
1213
RBr
ArSR
(ii) ArZ, CuI (10 mol%)
NaS
( 30 examples)
PEG200, 110 -130 °C
(iii) KOH, H2O
(i) NaOH(aq)
r.t.
S
Et2NH + CS2
Et2N
HCl (conc)
ArSSAr
( 6 examples)
Scheme 1. Reagents and conditions: Z = I, Br or OTs Ar = phenyl, 4-methylphenyl, 4-methoxyphenyl, naphthalen-1-yl, 4-trifluoromethylphenyl, 3,4-dichlorophenyl,
R = benzyl, n-butyl, cyclohexyl.
iodides, bromides, and tosylates were reacted with alkyl bromides
to produce the corresponding aryl alkyl thioethers in good to excel-
lent yields. In addition, the generation of diaryl disulfides occurred
in excellent yields using this method (Scheme 1).
Table 1
Optimization of the reaction conditions with respect to the effect of catalysts,
solvents, and the temperature on the formation of phenyl benzyl thioether from
iodobenzene and benzyl bromide
Entry
Catalyst
Solvent
Base
Temp (°C)
Yield (%)
Optimization of the conditions was performed on the reaction
of iodobenzene and benzyl bromide as a model system using dif-
ferent solvents, Cu and PdCl2/Ph3P catalysts, inorganic bases, CS2
and organic bases at two different temperatures (90 and 110 °C).
The results showed that when PEG200 was used as the solvent,
KOH as the inorganic base, CuI as the catalyst, and diethylamine
as an organic base with heating at 110 °C, the desired phenyl ben-
zyl thioether was isolated in an excellent yield (entry 4, Table 1).
According to the results in Table 1, all the copper salts catalyzed
the reaction but the most significant was CuI. Surprisingly, PdCl2/
PPh3 did not show any catalytic activity in this reaction. Among
the solvents, the most effective was PEG200 (entries 1–3, Table 1).
The temperature also affected the yield of the desired product
which ranged from 70% to 90% when the temperature was raised
from 90 to 110 °C (entries 2 and 4, Table 1). The effect of organic
bases on the reaction of iodobenzene with benzyl bromide showed
that the nature of the organic base was important affecting both
the pathway of the reaction and also the yield of the desired prod-
uct (Table 2). Among the organic bases the most effective was
diethylamine (Table 2).
When aryl iodides were reacted with alkyl bromides in PEG200,
under the optimized conditions, the reactions proceeded well to
produce the corresponding unsymmetrical thioethers in good to
excellent yields25 (Table 3).
Phenolic triflates are the most studied phenolic derivatives in
carbon–sulfur bond formation reactions.23 But other phenolic es-
ters such as tosylates may be more suitable precursors to be stud-
ied for C–S bond formation reactions. Thus, we studied the
reactions of phenolic tosylates under the optimized conditions at
130 °C. The reactions gave the corresponding aryl alkyl sulfides
in 65–75% isolated yields (Table 4).
1
2
3
4
5
6
7
8
9
CuI
CuI
CuI
CuI
DMF
PEG200
DMSO
PEG200
PEG200
PEG200
PEG200
PEG200
PEG200
PEG200
KOH
KOH
KOH
KOH
K2CO3
KOH
KOH
KOH
KOH
NaOH
90
90
90
110
110
110
110
110
110
110
50
70
50
90
70
60
70
75
NR
85
CuI
Cu(OAc)2
CuCl2
CuCl
PdCl2/PPh3
CuI
10
The bold letters represent the most effective reaction conditions.
Table 2
The effect of using different organic bases on the reaction of iodobenzene with benzyl
bromide
S
I
(i) Amine, CS2, r.t.
(ii) CuI (10 mol%), PEG200, 110 °C
a
S
(iii) KOH, H2O
(iv) PhCH2Br, r.t.
b
Entry
Amine
Base
Time (h)
Yielda (%)
Yieldb (%)
1
2
3
4
5
Et2NH
DBU
DBU
DABCO
Piperidine
KOH
—
KOH
—
20
15
15
24
24
92
35
55
NR
83
0
45
40
NR
0
KOH
The bold letters represent the most effective reaction conditions.
a
phenyl benzyl thioether.
diphenyl thio ether.
b
We have also studied the reaction of aryl bromides with alkyl
bromides for the formation of aryl alkyl thioethers. These reactions
Table 3
Aryl alkyl C–S bond formation by means of the reaction of aryl iodides and alkyl bromides using CS2 catalyzed by CuI in PEG200 at 110 °C
Entry
1
ArI
RBr
Product25
Time (h)
Yield (%)
92
1a
2a
20
5a
S
2
3
1b
1c
2a
2a
22
22
90
Me
S
5b
90
MeO
S
5c
(continued on next page)

1214
H. Firouzabadi et al. / Tetrahedron Letters 55 (2014) 1212–1217
Table 3 (continued)
Entry
ArI
RBr
Product25
Time (h)
20
Yield (%)
90
S
4
1d
2a
5d
5e
S
5
6
1a
1b
2b
2b
22
24
80
85
S
5f
Me
S
7
1d
2b
22
85
5g
S
8
9
1c
1a
1b
2b
2c
2c
24
22
24
75
75
75
5h
MeO
S
5i
S
10
5j
Me
S
11
1d
2c
22
75
5k
S
12
13
1c
1f
2c
2a
24
17
75
70
5l
MeO
Cl
Cl
S
S
5m
14
1e
1g
2a
2a
19
22
80
85
5n
F3C
Me
S
15
5o
Table 4
Aryl alkyl C–S bond generation by the reaction of aryl tosylates with alkyl bromides using CS2 catalyzed by CuI in PEG200 at 130 °C
Entry
1
ArOTs
RBr
Product
Time (h)
25
Yield (%)
75
3a
2a
S
5a
2
3
3b
3d
2a
2a
29
25
70
78
Me
S
5b
S
5d

H. Firouzabadi et al. / Tetrahedron Letters 55 (2014) 1212–1217
1215
Table 4 (continued)
Entry
ArOTs
RBr
Product
Time (h)
27
Yield (%)
S
4
5
3a
2b
2b
70
70
5e
S
3b
3d
31
27
5f
Me
S
S
6
2b
70
5g
7
8
3a
3b
2c
2c
27
31
65
65
5i
S
5j
Me
S
9
3d
2c
27
65
5k
proceeded smoothly at 130 °C to produce the desired thioethers in
55–65% isolated yields (Table 5).
mixture produces the desired aryl alkyl thioethers, and in the sec-
ond, neutralization of the reaction mixture with concentrated HCl
produces the corresponding diaryl disulfides in high yields27
(Table 6).
We have also shown that the method is suitable for larger scale
reactions. For this purpose, the reaction of iodobenzene (50 mmol)
with benzyl bromide (75 mmol), as a model reaction, was studied.
The reaction proceeded well within 20 h and the desired phenyl
benzyl sulfide was isolated in 83% yield.
Taking earlier work26 into account, we suggest that CS2 reacts
with diethylamine in the presence of an aqueous solution of NaOH
to produce sodium N,N-diethyldithiocarbamate, which in the pres-
ence of aryl compounds produces aryl N,N-diethyldithiocarbamate.
The resulting aryl N,N-diethyldithiocarbamate, after hydrolysis
with aqueous KOH solution can undergo two different reactions
(Scheme 2). In one, the addition of alkyl bromides to the reaction
In conclusion, we have presented a one-pot preparation of aryl
alkyl thioethers employing CS2 as the sulfur surrogate, diethyl-
amine as the base, and CuI as the catalyst in PEG200. This method
allows the conversion of aryl iodides, phenolic tosylates, and aryl
bromides to produce aryl alkyl thioethers in reasonably good to
Table 5
Aryl alkyl C–S bond formation via the reaction of aryl and alkyl bromides using CS2
catalyzed by CuI in PEG200
Entry
ArBr
RBr
Product
Time (h)
Yield (%)
1
4a
2a
29
65
S
5a
NaOH(aq)
r.t.
Na S
Et2N
(Et)2NH + CS2
S
S
2
3
4d
4a
2a
2b
29
31
50
65
ArSR
RBr
ArSK
5d
5e
ArZ
S
S
KOH
H2O
CuI
Et2N
SAr
S
S
Ar Cu
Z
I
I
4
5
4d
4a
2b
2c
31
31
55
55
air
HCl
Ar Cu
S
5g
ArSSAr
S
5i
Z
NEt2
Ar Cu
S
+ I
S
S
6
4d
2c
31
55
+ Z
NEt2
5k
Scheme 2.

1216
H. Firouzabadi et al. / Tetrahedron Letters 55 (2014) 1212–1217
Table 6
Diaryl disulfide formation using aryl compounds and CS2
Entry
ArIa/ArOTsb
Product27
Tempa,b (°C)
Timea,b (h)
20a/21b
Yielda,b (%)
90a/75b
S
S
1
1a/3a
110a/130b
S
5p
S
2
1d/3d
110a/130b
20a/22b
89a/70b
5q
S
3
4
1b/3b
110a/130b
22a/24b
89a/75b
S
5r
5s
S
1g
110
22
81a
S
a
aryl iodide.
aryl tosylate.
b
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excellent yields. This protocol also enables the preparation of
diaryl disulfides in excellent yields.
Acknowledgment
The authors are thankful for the support of this work by Grant
Number BN048 from the National Elite Foundation of Iran and
Shiraz University Research Council.
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.tetlet.2014.01.
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1217
25. Synthesis of (phenylmethylthio)benzene (5a); a typical procedure: A mixture of
CS2 (0.073 mL, 1.2 mmol), NaOH (1 mL) of a 10% solution, and diethylamine
(0.124 mL, 1.2 mmol) was stirred at room temperature for 1 h. Then CuI
(18 mg, 10 mol %), iodobenzene (0.112 mL, 1 mmol), and PEG200 (3 mL) were
added to the mixture which was stirred at 110 °C for 15 h. After complete
conversion of iodobenzene (TLC), a solution of KOH (224 mg, 4 mmol) and H2O
(0.2 mL) was added, and the mixture was heated at 110 °C for 4 h. After cooling
the reaction mixture to room temperature, benzyl bromide (256.5 mg,
1.5 mmol) was added and the mixture was stirred at room temperature for
1 h. H2O (5 mL) was added to the obtained mixture, and the product was
extracted with EtOAc (2 Â 5 mL). The combined organic extracts were dried
over anhydrous Na2SO4, and the solvent and volatiles were removed under
vacuum to give the crude product. Further purification was performed by
column chromatography on silica gel eluting with petroleum ether/EtOAc to
afford 5a in 92% yield (entry 1, Table 2). White crystals, Mp = 40 °C 1H NMR
2010, 39, 10338–10351; (c) Firouzabadi, H.; Iranpoor, N.; Gholinejad, M.;
Samadi, A. J. Mol. Catal. A: Chem. 2013, 377, 190–196.
27. Preparation of diphenyl disulfide (5p); a typical procedure: A mixture of CS2
(0.073 mL, 1.2 mmol), NaOH (1 mL, 10% solution), and diethylamine (0.124 mL,
1.2 mmol) was stirred at room temperature for 1 h. Next, CuI (18 mg,
10 mol %), iodobenzene (0.112 mL, 1 mmol), and PEG200 (3 mL) were added
to the mixture which was stirred at 110 °C for 15 h. After complete conversion
of the iodobenzene (TLC), a solution of KOH (224 mg, 4 mmol) in H2O (0.2 mL)
was added and the mixture was heated at 110 °C for 4 h. The resulting mixture
was cooled to room temperature. To the obtained mixture, HCl (2 mL, concd)
was added, while being cooled and stirred under air for 1 h in an ice-bath.
During the addition of acid, the stringent smell of thiophenol was detected. The
produced phenyl disulfide was extracted from the mixture with EtOAc
(2 Â 2 mL). The organic layer was washed with H2O (2 mL) and brine (3 mL)
and dried over Na2SO4. Removal of the solvent in vacuum provided diphenyl
disulfide with high purity (entry 1, Table 5). White crystals, Mp = 60 °C; 1H
NMR (250 MHz, CDCl3) d (ppm): 7.49–7.16 (m, 10H), 13C NMR (100 MHz,
CDCl3) d (ppm): 136.9, 129.0, 127.4, 127.1. Anal. Calcd for C12H10S2: C, 66.01; H,
4.62; S, 29.37. Found: C, 66.05; H, 4.57; S, 29.31.
(250 MHz, CDCl3)
d
(ppm): 7.38–7.18 (m, 10H), 4.16 (s, 2H), 13C NMR
(100 MHz, CDCl3) d (ppm): 137.4, 136.4, 129.7, 128.8, 128.5, 127.2, 126.3,
39.0. Anal. Calcd for C13H12S: C, 77.95; H, 6.04; S, 16.01; Found: C, 77.88; H,
6.02; S, 16.06.
26. (a) Beletskaya, I. P.; Cheprakov, A. V. Coord. Chem. Rev. 2004, 248, 2337–2364;
(b) Sperotto, E.; Van Klink, G. P. M.; Van Koten, G.; De Vries, J. G. Dalton Trans.