Electrochemical Synthesis of Thienoacene Derivatives: Transition-Metal-Free Dehydrogenative C?S Coupling Promoted by a Halogen Mediator

Article abstract of DOI:10.1002/anie.202001149

The first electrochemical dehydrogenative C?S bond formation leading to thienoacene derivatives is described. Several thienoacene derivatives were synthesized by dehydrogenative C?H/S?H coupling. The addition of ⁿBu₄NBr, which catalytically promoted the reaction as a halogen mediator, was essential.

Full text of DOI:10.1002/anie.202001149

A Journal of the Gesellschaft Deutscher Chemiker
Angewandte
Chemie
International Edition
www.angewandte.org
Accepted Article
Title: Electrochemical Synthesis of Thienoacene Derivatives: Transition
Metal-Free Dehydrogenative C–S Coupling Promoted by a
Halogen Mediator
Authors: Koichi Mitsudo, Ren Matsuo, Toki Yonezawa, Haruka Inoue,
Hiroki Mandai, and Seiji Suga
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: Angew. Chem. Int. Ed. 10.1002/anie.202001149
Angew. Chem. 10.1002/ange.202001149
Link to VoR: http://dx.doi.org/10.1002/anie.202001149
http://dx.doi.org/10.1002/ange.202001149

10.1002/anie.202001149
Angewandte Chemie International Edition
COMMUNICATION
Electrochemical Synthesis of Thienoacene Derivatives: Transition
Metal-Free Dehydrogenative C–S Coupling Promoted by a
Halogen Mediator
Koichi Mitsudo,*[a] Ren Matsuo,[a] Toki Yonezawa,[a] Haruka Inoue,[a] Hiroki Mandai,[b] and Seiji Suga*[a]
Abstract: The first electrochemical dehydrogenative C–S bond
formation leading to thienoacene derivatives is described. Several
thienoacene derivatives were synthesized via dehydrogenative C–
H/S–H coupling. The addition of nBu4NBr, which catalytically
promoted the reaction as a halogen mediator, was essential.
catalyzed dehydrogenative C–S coupling reactions have
attracted attention as an improved method for the formation of
C–S bonds with high atom-economy.[8]
Meanwhile, electrochemical carbon–heteroatom bond
formation is known to be as an environmentally benign strategy
that proceeds under mild conditions.[9] Recently, several novel
electrochemical carbon–heteroatom coupling reactions, such as
those for C–N[10] and C–O,[11] have been reported. For instance,
Lin and co-workers reported the 1,2-diazidation of alkenes,[10a]
and Baran reported electrochemical allylic oxidation.[11a,b]
Electrochemical approaches are also effective for C–S bond
formation.[12] Lei reported electro-oxidative intermolecular C–S
bond formation via C–H/S–H bond cleavage (Scheme 1 (i)).[12a]
Intramolecular dehydrogenative coupling between an arene and
a thiocarbonyl group was also effective for constructing C–S
The formation of a carbon–sulfur bond is one of the most
fundamental and significant transformations in organic synthesis
because C–S bonds are an abundant and significant skeleton in
the field of pharmaceuticals[1] and material science[2] (Figure 1).
Example compounds include the antidepressant vortioxetine,[3]
and an antifungal medication sertaconazole[4]. π-Expanded
benzo[b]thiophene derivatives, such as [1]benzothieno[3,2-
b][1]benzothiophene (BTBT)[5] and
dinaphtho[2,3-b:2’,3’-
d]thiophene (DNT),[6] have received considerable attention as
bonds
(Scheme
1
(ii)).[12d,g]
While
electrochemical
key building blocks for use in organic field effect transistors.
transformations have been studied intensively, to the best of our
knowledge, there has been no report on electrochemical
carbon–heteroatom bond formation for the construction of π-
expanded heteroacene derivatives, which are candidates for
useful organic materials.
We are interested in the development of new methods for
the synthesis of thienoacenes,[13] acene derivatives that contain
a
thiophene skeleton. We were inspired to investigate
electrochemical approaches[14] for the synthesis of thienoacenes.
We first assumed that intramolecular dehydrogenative C–H/S–H
coupling of 2-arylbenzene-1-thiol would form π-expanded
thiophenes, but the desired product was not obtained (Scheme 1
(iii)). During the course of further study, we eventually found that
the desired dehydrogenative C–S bond formation proceeded
smoothly in the presence of electrogenerated [Br+] as a powerful
promoter (Scheme 1 (iv)). This strategy was effective for the
Figure 1. Representative medicines and semiconductors having C–S bonds.
synthesis
of
π-expanded
thienoacenes
such
as
[1]benzothieno[3,2-b]benzo[2,3-d]furan (BTBF) and BTBT. We
report here the first electro-oxidative dehydrogenative C–S bond
formation promoted by electrogenerated [Br+] for the synthesis of
BTBFs and BTBTs.
One of the most conventional methods for the construction
of C–S bonds is transition metal-catalyzed cross-coupling
between aryl halides and thiols.[7] Recently, transition metal-
As a model compound, 2-(benzo[b]furan-2-yl)benzenethiol
(1a) was chosen and electro-oxidation was performed in 0.1 M
LiClO4 solution in CH3CN (Table 1). When simple electrolysis
without an additive was carried out at 25 °C, the desired cyclized
product 2a was not obtained and disulfide 3a was obtained in
42% yield (entry 1). We next included some additives. With 1.0
equiv of nBu4NBr at 25 °C, disulfide 3a was obtained in 73%
yield as a major compound along with the desired product 2a in
11% yield (entry 2). With an increase in the reaction temperature,
the yield of 2a increased: 90% yield at 60 °C (entry 4). At 70 °C,
the yield of 2a decreased to 62%, but then increased to 91%
with the use of 2.0 equiv of nBu4NBr (entry 5). The use of
[a]
[b]
Dr. K. Mitsudo, R. Matsuo, T. Yonezawa, Prof. Dr. S. Suga
Division of Applied Chemistry, Graduate School of Natural Science
and Technology, Okayama University
3-1-1 Tsushima-naka, Kita-ku, Okayama 700-8530 (Japan)
E-mail: mitsudo@okayama-u.ac.jp; suga@cc.okayama-u.ac.jp
Dr. H. Mandai
Department of Medical Technology, Gifu University of Medical
Science
4-3-3 Nijigaoka, Kani, Gifu 509-0293 (Japan)
Supporting information for this article is given via a link at the end of
the document.
This article is protected by copyright. All rights reserved.

10.1002/anie.202001149
Angewandte Chemie International Edition
COMMUNICATION
n
nBu4NCl and Bu4NI predominantly gave disulfide 3a (entries 6
and 7).
Table 1: Optimization of the additive for the electro-oxidation of 1a
Entry
Additive
Temp [°C]
2a [%][a]
3a [%][a]
1
2
3
4
5
6
7
none
25
25
50
60
70
60
60
0
42
nBu4NBr
nBu4NBr
nBu4NBr
nBu4NBr
nBu4NCl
nBu4NI
11
73
71
11
90 (89)[b]
62 (91)[b]
trace
0
4 (9)[b]
28 (trace)[b]
40
Scheme 1. Representative electrochemical dehydrogenative C–S bond
formation and this work
77
The product distribution strongly depends on the amount of
charge (Table 2). With 1.0 F mol−1 of charge (the theoretical
amount for one-electron oxidation of the substrate), while only a
trace amount of 2a was obtained, 3a was obtained in 96% yield
(entry 1). With an increase in the amount of charge, the yield of
3a decreased and that of 2a drastically increased. The yield of
2a reached 94% with 2.4 F mol−1 of charge (entry 4). During
further optimization, we found that the amount of charge could
be reduced by further stirring of the reaction mixture after
electrolysis. With 15 min of additional stirring after electrolysis at
2.0 F mol−1, 2a was obtained in an excellent yield (94% NMR
yield; 97% isolated yield). These results indicate that the electro-
oxidation of 1a initially gave 3a selectively, and 3a was then
converted to the desired product 2a. The latter transformation
should be slower than the first step, and required several
minutes to be finished. Since the conversion of 1a to 2a is a two-
electron oxidation, the electron efficiency of the reaction is quite
high.
[a] NMR yield. [b] Performed with 2.0 equiv of nBu4NBr.
Table 2: Effect of charge in the electro-oxidation of 1a
Entry
Charge [F mol−1
]
2a [%][a]
trace
3a [%][a]
1
2
3
4
1.0
1.5
2.0
2.4
96
We next reduced the amount of nBu4NBr for the electro-
oxidation (Table 3). With 0.5 equiv of nBu4NBr, the yield of 2a
decreased to 90% (entry 1). With a further decrease in the
amount of nBu4NBr (0.1–0.2 equiv), the yield of 2a drastically
decreased (entries 2 and 3). The low yield of 2a would be due to
the over-oxidation of 1a and 2a. To suppress this over-oxidation,
electro-oxidation was carried out with 2 mA of current. As
expected, the yield of 2a drastically improved to 93% (entry 4).
The amount of electrolyte could be reduced to 0.05 M (95%
yield).
17 (54)c
91 (94)[b] (97)[b,c]
94
76 (38)[b]
trace (0)[b]
N.D.
[a] NMR yield. [b] After electrolysis, the mixture was stirred for an additional
15 min. [c] Isolated yield.
This article is protected by copyright. All rights reserved.

10.1002/anie.202001149
Angewandte Chemie International Edition
COMMUNICATION
Under the optimized conditions, we examined the scope of
the reaction (Table 4). Precursors with an electron-donating
group such as a methyl group gave the cyclization products in
high yields (2b, 93%; 2c, 98%, 2d, 93%). When a precursor with
an electron-withdrawing group such as a fluoro group was used
in the reaction, the desired compound 2e was obtained in 94%
yield. More π-expanded compound was obtained by a similar
method. With a precursor bearing a naphthyl group, a five-ring
fused thienofuran 2f was obtained in 95% yield with 0.3 equiv of
nBu4NBr. With 0.1 equiv of nBu4NBr, decomposition of 2f took
place probably due to the low oxidation potential of 2f, but this
decomposition was suppressed by the use of 0.3 equiv of
nBu4NBr. A precursor bearing benzo[b]thiophene gave BTBT
(2g) in 98% yield. Several BTBT derivatives bearing electron-
donating or -withdrawing groups could be obtained in high yield
(2h–k). Benzo[b]thieno[2,3-d]thiophene derivatives 2l–n were
electrochemical reactions is that only a catalytic amount of
nBu4NBr, which is a low-toxic and stable compound, was
required for this reaction.
Table 4: Electro-oxidative dehydrogenative cyclization of several precursors for
the synthesis of 2 under the optimized conditions[a]
also obtained in excellent yield.
A
more π-expanded
thienothiophene such as 2o was readily obtained from a
corresponding precursor which has two thiols.
Table 3: Electro-oxidation of 1a with catalytic amount of nBu4NBr
Entry
nBu4NBr [equiv]
Current [mA]
2a [%][a]
90
1
2
3
4
0.5
0.2
0.1
0.1
12
12
12
2
37
11
93 (95)[b]
[a] Isolated yield. [b] With 0.3 equiv of nBu4NBr. [c] With nBu4NBr (2.0 equiv) and
LiClO4 (0.1 M). 12 mA, 2.0 F mol−1. [d] With nBu4NBr (4.0 equiv) and LiClO4 (0.1
M). 12 mA, 8.0 F mol−1
[a] NMR yield. [b] With 0.05 M of LiClO4.
To gain further insight into the reaction mechanism, we
performed some control experiments (Scheme 2). Without
electrolysis, 1a was not converted to 2a, and mostly 1a was
recovered, (Scheme 2 (i)). We also attempted a reaction of 1a
with NBS without electrolysis. Under the conditions, 2a was
obtained in only 20% yield and dibrominated by-product 4a was
obtained in 20% yield (Scheme 2 (ii)). The reaction with 1.0
equiv of Br2 instead of NBS gave disulfide 3a quantitatively.
Further addition of Br2 (2.0 equiv) gave 2a in 87% yield.[15] We
also tried to use nBu4NBr3, and found that 2a was obtained
quantitatively, while a stoichiometric amount of nBu4NBr3 was
required. While the exact structure of [Br+] generated in situ is
not yet clear, the behavior of [Br+] should be similar to that of
Br3−. This result was consistent with that of Nonaka’s work on
[Br+].[16] While similar C–S bond formations proceed with Br2 and
nBu4NBr3 instead of electrolysis, stoichiometric amounts of these
reagents are required to accomplish the chemical
transformations. In contrast, an advantage of Br−-promoted
According to the results shown in Table 2, 3a should be the
intermediate for the synthesis of 2a from 1a. Electro-oxidation of
3a was carried out under similar conditions. When 2.0 F mol−1 of
charge was passed, 3a was completely consumed and 2a was
obtained in 92% yield (Scheme 2 (iii)). These results clearly
indicate that 1a was converted to 2a through 3a.
To clarify the role of nBu4NBr as a promoter of the
transformation, the electrochemical properties of 1a, 2a, 3a, and
nBu4NBr were studied using cyclic voltammetry (Figure S2). The
oxidation potential of nBu4NBr was the most negative (Eonset
=
0.25 V), and Eonset of 1a (0.83 V) was more negative than those
of 2a (0.96 V) and 3a (0.99 V). These results suggest that the
n
oxidation of Bu4NBr should occur first, and the oxidation of 1a
would be preferred compared to those of 2a and 3a. In the cyclic
voltammograms of the mixture of 1a and nBu4NBr, a catalytic
current was observed.[17] This result suggests that a cationic
species generated from Br− would oxidize 1a.
This article is protected by copyright. All rights reserved.

10.1002/anie.202001149
Angewandte Chemie International Edition
COMMUNICATION
Figure 3. A plausible mechanism for the dehydrogenative cyclization of 1a.
Acknowledgements
This work was supported in part by JSPS KAKENHI Grant
Number JP19K05477, JP19K05478 and JP18H04455 in Middle
Molecular Strategy, Okayama Foundation for Science and
Technology, and by Electric Technology Research Foundation
of Chugoku.
Scheme 2. Control experiments
Keywords: Electrochemistry • Sulfur heterocycles • C–S bond
formation • Cross-coupling • Cyclization
Based on these experiments, a plausible mechanism for the
electro-oxidative dehydrogenative cyclization of 1 is illustrated in
Figure 3. First, Br− of nBu4NBr would be oxidized to afford
[Br+].[16,18] 1 would be oxidized by [Br+] to give disulfide 3 and Br−,
which would be oxidized to [Br+] again on the anode. Next,
disulfide 3 would react with [Br+] to give cationic species A.
Subsequent intramolecular cyclization would give cyclized
product B and arylthiobromide C. Subsequent deprotonation of
[1]
[2]
a) R. S. Keri, K. Chand, S. Budagumpi, S. Balappa Somappa, S. A.
Patil, B. M. Nagaraja, Eur. J. Med. Chem. 2017, 138, 1002; b) E. A.
Ilardi, E. Vitaku, J. T. Njardarson, J. Med. Chem. 2014, 57, 2832.
a) F. Dikcal, T. Ozturk, M. E. Cinar, Org. Commun. 2017, 10, 56; b) L.
Li, C. Zhao, H. Wang, Chem. Rec. 2016, 16, 797; c) K. Takimiya, M.
Nakano, H. Sugino, I. Osaka, Synth. Met. 2016, 217, 68; d) M. E. Cinar,
T. Ozturk, Chem. Rev. 2015, 115, 3036.
the intermediate
B would give the desired product 2.
[3]
a) V. Magne, L. T. Ball, Chem. - Eur. J. 2019, 25, 8903; b) R. N. Gaykar,
S. Bhattacharjee, A. T. Biju, Org. Lett. 2019, 21, 737; c) J.-A. García-
López, M. Çetin, M. F. Greaney, Angew. Chem., Int. Ed. 2015, 54,
2156; d) B. Bang-Andersen, T. Ruhland, M. Jørgensen, G. Smith, K.
Frederiksen, K. G. Jensen, H. Zhong, S. M. Nielsen, S. Hogg, A. Mørk,
T. B. Stensbøl, J. Med. Chem. 2011, 54, 3206.
Intermediate C would be oxidized by anodic oxidation or [Br+] to
give disulfide 3, which would react with [Br+] to give A. The
cathodic reaction would be the generation of hydrogen from H+.
In conclusion, we have developed the first method for the
construction of BTBFs and BTBTs by electro-oxidative
dehydrogenative cyclization promoted by [Br+]. This method
realizes the construction of π-expanded thienoacenes under
transition metal-free and mild conditions with a catalytic amount
of halogen mediator. The scope of this methodology is under
investigation in our laboratory.
[4]
[5]
a) M. Goldust, E. Rezaee, S. Masoudnia, R. Raghifar, Ann Parasitol
2013, 59, 119; b) T. Al Nakib, M. J. Meegan, M. L. Burke, J. Chem.
Res., Synop. 1994, 170; c) M. Raga, C. Palacin, J. M. Castello, J. A.
Ortiz, M. R. Cuberes, M. Moreno-Manas, Eur. J. Med. Chem. 1986, 21,
329.
Selected papers: a) Y. Yuan, G. Giri, A. L. Ayzner, A. P. Zoombelt, S. C.
B. Mannsfeld, J. Chen, D. Nordlund, M. F. Toney, J. Huang, Z. Bao,
Nat. Commun. 2014, 5, 3005; b) H. Ebata, T. Izawa, E. Miyazaki, K.
Takimiya, M. Ikeda, H. Kuwabara, T. Yui, J. Am. Chem. Soc. 2007, 129,
15732; c) C. Grigoriadis, C. Niebel, C. Ruzie, Y. H. Geerts, G. Floudas,
J. Phys. Chem. B 2014, 118, 1443.
[6]
a) T. Okamoto, C. Mitsui, M. Yamagishi, K. Nakahara, J. Soeda, Y.
Hirose, K. Miwa, H. Sato, A. Yamano, T. Matsushita, T. Uemura, J.
Takeya, Adv. Mater. 2013, 25, 6392–6397; b) I. Piquero-Zulaica, J.
This article is protected by copyright. All rights reserved.

10.1002/anie.202001149
Angewandte Chemie International Edition
COMMUNICATION
Lobo-Checa, A. Sadeghi, Z. M. Abd El-Fattah, C. Mitsui, T. Okamoto, R.
Pawlak, T. Meier, A. Arnau, J. E. Ortega, J. Takeya, S. Goedecker, E.
Meyer, S. Kawai, Nat. Commun. 2017, 8, 787.
2017, 19, 2092; d) A. A. Folgueiras-Amador, X. Y. Qian, H. C. Xu, T.
Wirth, Chem. - Eur. J. 2018, 24, 487; e) S. Liang, C.-C. Zeng, H.-Y.
Tian, B.-G. Sun, X.-G. Luo, F.-z. Ren, Adv. Synth. Catal. 2018, 360,
1444; f) D. Liu, H. X. Ma, P. Fang, T. S. Mei, Angew. Chem. Int. Ed.
2019, 58, 5033; Angew. Chem. 2019, 131, 5087; g) C. Huang, X. Y.
Qian, H. C. Xu, Angew. Chem. Int. Ed. 2019, 58, 6650; Angew. Chem.
2019, 131, 6722.
[7]
[8]
C.-F. Lee, Y.-C. Liu S. S. Badsara, Chem. Asian J. 2014, 706–722.
Selected papers: a) C. Dai, Z. Xu, F. Huang, Z. Yu, Y.-F. Gao, J. Org.
Chem. 2012, 77, 4414; b) S. Ranjit, R. Lee, D. Haryadi, C. Shen, J. Wu,
P. Zhang, K.-W. Huang, X. Liu, J. Org. Chem., 2011, 76, 8999; c) T.
Gensch, F. J. R. Klauck, F. Glorius, Angew. Chem. Int. Ed. 2016, 55,
11287; Angew. Chem. 2016, 128, 11457; d) M. Iwasaki, Y. Nishihara,
Dalton Trans. 2016, 45, 15278–15284; e) S. Maity, U. Karmakar, R.
Samanta, Chem. Commun. 2017, 53, 12197; f) A. Mandal, S. Dana, H.
Sahoo, G. S. Grandhi, M. Baidya, Org. Lett. 2017, 19, 2430; g) S. P.
Yang, B. Y. Feng, Y. D. Yang, J. Org. Chem. 2017, 82, 12430; h) Y. S.
Kang, P. Zhang, M. Y. Li, Y. K. Chen, H. J. Xu, J. Zhao, W. Y. Sun, J. Q.
Yu, Y. Lu, Angew. Chem. Int. Ed. 2019, 58, 9099; Angew. Chem. 2019,
131, 9197.
[13] a) K. Mitsudo, S. Tanaka, R. Isobuchi, T. Inada, H. Mandai, T.
Korenaga, A. Wakamiya, Y. Murata, S. Suga, Org. Lett. 2017, 19, 2564;
b) K. Mitsudo, Y. Kurimoto, H. Mandai, S. Suga, Org. Lett. 2017, 19,
2821; c) K. Mitsudo, H. Sato, A. Yamasaki, N. Kamimoto, J. Goto, H.
Mandai, S. Suga, Org. Lett. 2015, 17, 4858; d) K. Mitsudo, S.
Shimohara, J. Mizoguchi, H. Mandai, S. Suga, Org. Lett. 2012, 14,
2702.
[14] a) K. Mitsudo, J. Yamamoto, T. Akagi, A. Yamashita, M. Haisa, K.
Yoshioka, H. Mandai, K. Ueoka, C. Hempel, J. Yoshida, S. Suga,
Beilstein J. Org. Chem. 2018, 14, 1192; b) N. Kamimoto, N. Nakamura,
A. Tsutsumi, H. Mandai, K. Mitsudo, A. Wakamiya, Y. Murata, J.
Hasegawa, S. Suga, Asian J. Org. Chem. 2016, 5, 373; c) K. Mitsudo,
N. Kamimoto, H. Murakami, H. Mandai, A. Wakamiya, Y. Murata, S.
Suga, Org. Biomol. Chem. 2012, 10, 9562; d) K. Mitsudo, T. Shiraga, J.
Mizukawa, S. Suga, H. Tanaka, Chem. Commun. 2010, 46, 9256; e) K.
Mitsudo, T. Kaide, E. Nakamoto, K. Yoshida, H. Tanaka, J. Am. Chem.
Soc. 2007, 129, 2246.
[9]
a) M. Yan, Y. Kawamata, P. S. Baran, Chem. Rev. 2017, 117, 13230;
b) J. Yoshida, A. Shimizu, R. Hayashi, Chem. Rev. 2018, 118, 4702; c)
S. R. Waldvogel, B. Janza, Angew. Chem. Int. Ed. 2014, 53, 7122;
Angew. Chem. 2014, 53, 7122; d) H. Wang, X. Gao, Z. Lv, T. Abdelilah,
A. Lei, Chem. Rev. 2019, 119, 6769.
[10] Representative reports: a) N. Fu, G. S. Sauer, A. Saha, A. Loo, S. Lin,
Science 2017, 357, 575; b) M. Gong, J.-M. Huang, Chem. - Eur. J.
2016, 22, 14293; c) L.-S. Kang, M.-H. Luo, C. M. Lam, L.-M. Hu, R. D.
Little, C.-C. Zeng, Green Chem. 2016, 18, 3767; d) P. Qian, J.-H. Su, Y.
Wang, M. Bi, Z. Zha, Z. Wang, J. Org. Chem. 2017, 82, 6434; e) H.-B.
Zhao, Z.-W. Hou, Z.-J. Liu, Z.-F. Zhou, J. Song, H.-C. Xu, Angew.
Chem., Int. Ed. 2017, 56, 587; Angew. Chem. 2017, 129, 602; f) A.
Kehl, V. M. Breising, D. Schollmeyer, S. R. Waldvogel, Chem. - Eur. J.
2018, 24, 17230; g) J. Li, W. Huang, J. Chen, L. He, X. Cheng, G. Li,
Angew. Chem., Int. Ed. 2018, 57, 5695; Angew. Chem. 2018, 130,
5797; h) S. Zhang, L. Li, M. Xue, R. Zhang, K. Xu, K. Xu, C. Zeng, Org.
Lett. 2018, 20, 3443–3446; i) X. Chang, Q. Zhang, C. Guo, Org. Lett.
2019, 21, 10–13; l) M.-L. Feng, S.-Q. Li, H.-Z. He, L.-Y. Xi, S.-Y. Chen,
X.-Q. Yu, Green Chem. 2019, 21, 1619; j) Y. Liu, L. Xue, B. Shi, F. Bu,
D. Wang, L. Lu, R. Shi, A. Lei, Chem. Commun. 2019, 55, 14922.
[11] a) E. J. Horn, B. R. Rosen, Y. Chen, J. Tang, K. Chen, M. D. Eastgate,
P. S. Baran, Nature 2016, 533, 77; b) Y. Kawamata, M. Yan, Z. Liu, D.-
H. Bao, J. Chen, J. T. Starr, P. S. Baran, J. Am. Chem. Soc. 2017, 139,
7448–7451; b) Y. Shih, C. Ke, C. Pan, Y. Huang, RSC Adv. 2013, 3,
7330–7336; c) S. Zhang, F. Lian, M. Xue, T. Qin, L. Li, X. Zhang, K. Xu,
Org. Lett. 2017, 19, 6622; d) S. Zhang, L. Li, H. Wang, Q. Li, W. Liu, K.
Xu, C. Zeng, Org. Lett. 2018, 20, 252; e) L. Zhang, Z. Zhang, J. Zhang,
K. Li, F. Mo, Green Chem. 2018, 20, 3916.
[15] An iodine-mediated dehydrogenative cyclization of 1a leading to BTBF
was already reported, but the use of excess amount of iodine (3 equiv),
high reaction temperature (dioxane, reflux) and long reaction time (72
h) were required and only 21% yield of BTBF was obtained: K.
Cernovska, M. Nic, P. Pihera, J. Svoboda, Collect. Czech. Chem.
Commun. 2000, 65, 1939.
–
[16] Br3 would be a potent candidate of [Br+] under the conditions, see: T.
Takiguchi, T. Nonaka, Bull. Chem. Soc. Jpn. 1987, 60, 3137.
[17] For the cyclic voltammograms, see the Supporting Information.
[18] a) S. Torii, Electroorganic Syntheses, Methods, and Applications, Part
1: Oxidations, Kodansha & VCH, Tokyo & Wainheim, 1985; b) T. Shono,
Y. Matsumura, K. Inoue, J. Am. Chem. Soc. 1984, 106, 6075; c) M.
Kimura, N. Kuriki, M. Inaishi, Y. Sawaki, Tetrahedron Lett. 1984, 25,
4665; e) K. F. Babu, R. Sivasubramanian, M. Noel, M. A.
Kulandainathan, Electrochim. Acta 2011, 56, 9797; d) T. Inokuchi, S.
Matsumoto, S. Torii, J. Org. Chem. 1991, 56, 2416; e) S. Torii, K.
Uneyama, H. Tanaka, T. Yamanaka, T. Yasuda, M. Ono, Y. Kohmoto, J.
Org. Chem. 1981, 46, 3312; f) K. Mitsudo, T. Kawaguchi, S. Miyahara,
W. Matsuda, M. Kuroboshi, H. Tanaka, Org. Lett. 2005, 7, 4649; g) K.
Fujimoto, H. Maekawa, Y. Matsubara, I. Nishiguchi, Chem. Lett. 1996,
25, 143.
[12] a) P. Wang, S. Tang, P. Huang, A. Lei, Angew. Chem. Int. Ed. 2017, 56,
3009; Angew. Chem. 2017, 56, 3055. b) K. A. Ogawa, A. J. Boydston,
Org. Lett. 2014, 16, 1928; c) P. Wang, S. Tang, A. W. Lei, Green Chem.
This article is protected by copyright. All rights reserved.

10.1002/anie.202001149
Angewandte Chemie International Edition
COMMUNICATION
Entry for the Table of Contents
COMMUNICATION
Koichi Mitsudo,* Ren Matsuo, Toki
Yonezawa, Haruka Inoue, Hiroki
Mandai, and Seiji Suga*
Page No. – Page No.
Electrochemical Synthesis of
Thienoacene Derivatives: Transition
Metal-Free Dehydrogenative C–S
Coupling Promoted by a Halogen
Mediator
Electrochemical intramolecular C–S bond formation leading to derivatives is
achieved. Bromide catalytically promoted the reaction as a halogen mediator.
This article is protected by copyright. All rights reserved.