Straightforward access to aryl-substituted/fused 1,3-dithiole-2- chalcogenones by Cu-catalyzed C-S coupling between aryl iodides and zinc-thiolate complex (TBA)2[Zn(DMIT)2]

Article abstract of DOI:10.1039/c3ra41349g

The Cu-catalyzed C-S coupling between iodoaryl and a zinc-thiolate complex was achieved. This protocol provides a facile and efficient synthetic approach for aryl-substituted/fused 1,3-dithiole-2-chalcogenones, which can be converted to TTFs. The Royal Society of Chemistry 2013.

Full text of DOI:10.1039/c3ra41349g

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Straightforward access to aryl-substituted/fused 1,3-
dithiole-2-chalcogenones by Cu-catalyzed C–S
coupling between aryl iodides and zinc–thiolate
complex (TBA)2[Zn(DMIT)2]3
Cite this: RSC Advances, 2013, 3, 10193
Received 19th March 2013,
Accepted 9th May 2013
DOI: 10.1039/c3ra41349g
Jibin Sun,a Xiaofeng Lu,a Jiafeng Shao,b Zili Cui,a Yu Shao,a Guiyang Jiang,a Wei Yua
and Xiangfeng Shao*a
www.rsc.org/advances
The Cu-catalyzed C–S coupling between iodoaryl and a zinc–
thiolate complex was achieved. This protocol provides a facile and
efficient synthetic approach for aryl-substituted/fused 1,3-
dithiole-2-chalcogenones, which can be converted to TTFs.
thiones. It should be noted that the sulphur sources in most of the
C–S coupling reactions are limited to thiols or their precursors.5
Therefore, the present protocol, using ambient stable and
odourless zinc–thiolate as a sulphur source, would be attractive
from the synthetic viewpoint.
The extension of p-electron conjugation of tetrathiafulvalene (TTF)
offers a powerful opportunity to adapt TTFs for different
applications.1 In this context, the peripheral substitution/fusion
of aromatic system to TTF framework is one promising method
because the aryls can (1) influence the electronic nature of parent
TTF through the extension of p-conjugation, and (2) lead to new
packing motifs by p–p interaction. To date, the aryls and TTF are
mainly connected via the C–C bond,2 whereas few reports concern
their connection via the sulphur bridge due to the synthetic
difficulty.3 It is known that the most effective synthetic method for
TTFs is the phosphate-mediated coupling reaction of 1,3-dithiole-
2-chalcogenones.4 Thus, the key step for the synthesis of aryl-
substituted/fused TTFs via sulphur bridge is to prepare the
corresponding 1,3-dithiole-2-chalcogenones. Unfortunately, the
reported methods for the incorporation of aryls onto 1,3-
dithiole-2-chalcogenones via sulphur bridge suffer from the
narrow scope and low yield.3 It is therefore highly desirable to
solve this synthetic problem.
We carried out the Cu2O-catalyzed C–S coupling reaction
between halogenobenzene and (TBA)2[Zn(DMIT)2] under similar
conditions to those reported for the typical C–S coupling reaction
(in DMF at 120 uC).5e It was found that chlorobenzene and
bromobenzene did not afford the desired product 1a, thus
iodobenzene was used to optimize the reaction conditions as
summarized in Table 1. Since (TBA)2[Zn(DMIT)2] has four thiolate
anions, the molar ratio of (TBA)2[Zn(DMIT)2] : iodobenzene was
set as 1 : 4.4. Further increasing the amount of iodobenzene did
not afford better yield of 1a. The ratio of Cu2O : ligand was set as
1 : 2.5e
Several ligands (L1–L5) were screened with Cu2O (20%)
(Table 1, Entries 1–5), among which ethyl acetoacetate (L2) gave
the best result (isolated yield of 1a, 77%). Surprisingly, 1a can also
be obtained in 50% even without adding any ligands (Entry 6). On
the other hand, when (TBA)2[Cu(DMIT)2] was directly used as
reactant without adding Cu2O and ligand, 1a was obtained only in
25%. The reaction was run with different copper salts other than
Cu2O (Entries 7–14), but the yield of 1a was less than 60%.
Additionally, the amount of Cu2O showed significant influence on
this reaction (Entries 15–19). The reaction did not take place in the
absence of Cu2O. The yield of 1a became higher as the amount of
Cu2O increased and reached to the maximum of 77% when Cu2O
was 20%, but it could not be further improved by increasing Cu2O
to over 25%.
The copper-catalyzed C–S coupling has attracted considerable
attention.5 We envisioned that this reaction would be applicable to
synthesize the aryl-substituted/fused 1,3-dithiole-2-thiones via
sulphur bridge. Herein, we disclose the Cu-catalyzed C–S coupling
between aryl halides and a readily available zinc–thiolate complex
(TBA)2[Zn(DMIT)2]6 (see Scheme 1), which is further employed to
the preparation of a variety of aryl-substituted/fused 1,3-dithiole-2-
The influence of the reaction temperature (Entries 20–23) and
time (Entries 24–27) were also examined. The yield of 1a dropped
dramatically when the temperature was below 100 uC or the
reaction time was shorter than 10 h. However, the yield of 1a did
not improve any more by further increasing the temperature to
more than 120 uC or extending reaction time to more than 10 h.
This reaction also took place in DMSO with the yield of 1a (65%)
lower than in DMF. By contrast, the reaction did not proceed in
aState Key Laboratory of Applied Organic Chemistry & School of Chemistry and
Chemical Engineering, Lanzhou University, Lanzhou 730000, P. R. China.
E-mail: shaoxf@lzu.edu.cn; Fax: +86 0931 8915557; Tel: +86 0931 8912500
bSchool of Physical Science and Technology, Lanzhou University, Lanzhou 730000, P.
R. China
Electronic supplementary information (ESI) available: Chemical structures,
3
additional experimental procedures, characterisation data, X-ray crystallographic
data. CCDC reference numbers 922049–922052. For ESI and crystallographic data in
CIF, see DOI: 10.1039/c3ra41349g
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Scheme 1 Synthetic approach for the aryl-substituted/fused 1,3-dithiole-2-thiones via sulphur bridge.
toluene, CH3CN, and 1,4-dioxane. Thus, the optimized reaction
conditions are Cu2O(20%)/L2(40%)/DMF/120 uC/10 h.
To study the scope of this methodology and its application in
the synthesis of aryl substituted 1,3-dithiole-2-thiones, the reaction
Table 1 Optimization of the reaction conditions between iodobenzene and
(TBA)2[Zn(DMIT)2]a
Table 2 Synthesis of the aryl-substituted 1,3-dithiole-2-thiones via sulphur
bridgea
Ar
1,3-Dithiole-2-thione
Yield (%)b
C6H5
1a
2a
3a
4a
5a
6a
7a
8a
77
66
70
67
56
75
58
64
70
75
60
70
60d
55
65
53
85
50
50
70
76
50
78
91
50
56
70
90
60
C6H4-2-Me
C6H4-4-Me
C6H4-3-Me
C6H4-2-OMe
C6H4-4-OMe
C6H4-3-OMe
C6H4-4-NMe2
C6H4-2-NHC(O)CH3
C6H4-2-Cl
C6H4-4-Cl
C6H4-3-Cl
C6H4-2-Br
C6H4-4-Br
Entry Cu source (%)
Ligand (%) T (uC) Time (h) Yield of 1a (%)b
1
2
3
4
5
6
7
8
Cu2O (20)
Cu2O (20)
Cu2O (20)
Cu2O (20)
Cu2O (20)
Cu2O (20)
CuCl (20)
CuBr (20)
CuI (20)
CuBr2 (20)
CuSO4 (20)
Cu(OAc)2?H2O (20) L2 (40)
CuSO4?5H2O (20) L2 (40)
CuCl2?2H2O (20) L2 (40)
L1 (40)
L2 (40)
L3 (40)
L4 (40)
L5 (40)
—
L2 (40)
L2 (40)
L2 (40)
L2 (40)
L2 (40)
120 10
120 10
120 10
120 10
120 10
120 10
120 10
120 10
120 10
120 10
120 10
120 10
120 10
120 10
120 10
120 10
120 10
120 10
120 10
60 10
72
77
69
56
57
50
60
55
58
45
38
60
48
40
0
43
59
65
64
0
Trace
53
69
16
31
50
73
9a
10a
11a
12a
13ac
14a
15a
16ac
17ae
18a
19a
20a
21ae
22a
23a
24ae
25a
26a
27a
28ae
29a
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
C6H4-3-Br
C6H4-4-I
C6H4-2-CO2Me
C6H4-4-CO2Me
C6H4-3-CO2Me
C6H4-4-CO2Et
C6H4-2-COMe
C6H4-4-COMe
C6H4-2-CN
C6H4-2-NO2
C6H4-3-NO2
4-Biphenyl
2-Thienyl
Cu2O (0)
Cu2O (5)
L2 (40)
L2 (10)
L2 (20)
L2 (30)
L2 (50)
L2 (40)
L2 (40)
L2 (40)
L2 (40)
L2 (40)
L2 (40)
L2 (40)
L2 (40)
Cu2O (10)
Cu2O (15)
Cu2O (25)
Cu2O (20)
Cu2O (20)
Cu2O (20)
Cu2O (20)
Cu2O (20)
Cu2O (20)
Cu2O (20)
Cu2O (20)
80 10
100 10
150 10
120
120
120
2.5
5.0
7.5
2-Pyridyl
3-Pyridyl
a
Reaction conditions: (TBA)2[Zn(DMIT)2] (1.69 mmol), Ar-I (7.44
mmol), Cu2O (0.34 mmol), L2 (ethyl acetoacetate, 0.68 mmol), DMF
120 12.5
a
b
c
Reagents: (TBA)2[Zn(DMIT)2] (1.69 mmol), iodobenzene (7.44
(3 mL), 120 uC, 10 h. Isolated yield. Aryl iodide was set as 6 eq.
b
d
e
mmol), DMF (3 mL). Isolated yield.
23% of 30a was also isolated. Reaction temperature was 80 uC.
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Table 3 Synthesis of the aryl-fused 1,3-dithiole-2-thiones via sulphur bridgea
Table 4 Synthesis of the aryl substituted TTFs via sulphur bridgea
Ar1
Ar2
TTFs
Yield (%)b
Phenyl
Phenyl
TTF-1
TTF-2
TTF-3
TTF-4
TTF-5
92
80
93
80
75
2-Pyridyl
2-Thienyl
2-Pyridyl
2-Pyridyl
2-Pyridyl
2-Thienyl
Phenyl
2-Thienyl
a
b
Experimental details are supplied in ESI. Isolated yield.
3
did not react with (TBA)2[Zn(DMIT)2] even at higher temperature.
We also carried out the synthesis of asymmetric 1,3-dithiole-2-
thiones (38a–40a) via the three-component tandem procedure, the
yield of the desired product is about 40% (see ESI for the
experimental and structural details).
3
a
Reaction conditions: (TBA)2[Zn(DMIT)2] (1.69 mmol), aryl ortho-
diiodide (3.5 mmol), Cu2O (0.34 mmol), L2 (0.68 mmol), DMF (3
The resulting aryl-substituted/fused 1,3-dithiole-2-thiones were
converted into the corresponding 1,3-dithiole-2-ones (1b–37b) by
reaction with Hg(OAc)2,4 and most of the transformations were
almost quantitative. The single crystals of 17b, 24b, 34a and 35a
were obtained by slowly evaporating the solvent. Fig. 1 depicts the
crystal structure of 34a, and those of 17b, 24b, and 35a are shown
mL), 80 uC, 10 h.
of (TBA)2[Zn(DMIT)2] with a number of aryl iodides (ortho-
diiodides) was carried out as summarized in Tables 2 and 3. In
this synthetic approach, all types of aryl iodides, including the
electron-donating, electron-withdrawing, and sterically hindered
ortho-substituted aryl iodides, are well tolerated. Most of the aryl
iodides can be transformed to the corresponding aryl substituted
1,3-dithiole-2-thiones in ¢60%. Remarkably, the reaction can be
run at lower temperature (80 uC) with better yield when the ortho-
substituent is electron-withdrawing group (17a, 21a, 24a), and the
highest yield is 91% for 24a. Heteroaryl iodides also provided good
results for the synthesis of 1,3-dithiole-2-thiones (27a–29a). In
particular, 2-iodopyridine was transformed to the desired product
28a at 80 uC with 90% yield. In the case of ortho-diiodoaryls, the
corresponding aryl-fused 1,3-dithiole-2-thiones can be obtained in
¢65% (30a–37a). It should be noted that 1-bromo-2-iodobenzene
can simultaneously afford 30a with 23% yield during the
in ESI (Fig. S1–S3). On the basis of the resulting 1,3-dithiole-2-
3
chalcogenones, we have prepared a variety of aryl substituted/
fused TTFs through the typical approach of phosphate-mediated
coupling reaction, and the selected results are summarized in
Table 4 (see ESI for further details). The isolated yields for all
3
these TTFs were over 75%.
In conclusion, we have developed a straightforward synthetic
method for the aryl substituted/fused 1,3-dithiole-2-thiones via
sulphur bridge by using Cu-catalyzed C–S coupling between the
aryl iodides and zinc–thiolate complex (TBA)2[Zn(DMIT)2]. This
protocol enables us to create a library of TTFs incorporating aryls
via sulphur bridge in low cost and large substituent scope. The
present work also suggests that the zinc–thiolate complex, which
is ambient stable and without foul smell, would be a promising
sulphur source in Cu-catalyzed S-arylation. The investigation of the
optical and electrochemical properties, as well as the solid state
structures of the aryl substituted/fused TTFs are in progress and
will be reported in due course.
preparation
of
13a.
Meanwhile,
the
reaction
of
(TBA)2[Zn(DMIT)2] with 1-chloro-2-iodobenzene under the same
conditions exclusively provided 10a, and ortho-dibromobenzene
The authors acknowledge the financial support from NSFC
(21003067, 21172104, and 21190034). We are grateful to Prof. Z.-Q.
Liu (SKLAOC, Lanzhou University) for valuable suggestion on Cu-
catalyzed C–S coupling reaction.
Notes and references
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