Synthesis of 2-aryl-benzothiazoles via Ni-catalyzed coupling of benzothiazoles and aryl sulfamates

Article abstract of DOI:10.1515/hc-2020-0001

2-Aryl-benzothiazoles have been successfully synthesized via a simple coupling reaction between benzothiazoles and aryl sulfamates using a nickel catalyst. The nickel catalyst is inexpensive, reusable and commercially available. In addition, the use of highly expensive palladium catalysts and unstable raw materials has been avoided. 2-Aryl-benzothiazoles bearing various substituents on the aryl groups were obtained in good yield.

Full text of DOI:10.1515/hc-2020-0001

Heterocycl. Commun. 2020; 26: 1–5
Research Article
Open Access
Xiaofeng Yu*, Zhen Zhang, Renyuan Song, Liping Gou and Guangrong Wang
Synthesis of 2-aryl-benzothiazoles via
Ni-catalyzed coupling of benzothiazoles and
aryl sulfamates
https://doi.org/10.1515/hc-2020-0001
disadvantageous because 2-aminothiophenol is extre-
mely unstable in air and highly toxic. In addition, benzyl
Received October 28, 2019; accepted December 02, 2019.
Abstract: 2-Aryl-benzothiazoles have been successfully alcohol, benzylamine and aromatic aldehydes are also
synthesized via a simple coupling reaction between ben- very reactive materials.
zothiazoles and aryl sulfamates using a nickel catalyst.
Recent studies have shown that novel synthetic
The nickel catalyst is inexpensive, reusable and commer- methods which involve the direct coupling of benzothia-
cially available. In addition, the use of highly expensive zoles with arylating agents avoid the use of highly toxic
palladium catalysts and unstable raw materials has been and reactive materials. But, there are some disadvantages
avoided. 2-Aryl-benzothiazoles bearing various substitu- in these reports, such as using expensive palladium as a
ents on the aryl groups were obtained in good yield.
catalyst [28, 29], and the use of unstable aromatic iodides
[29] or aromatic aldehydes [30] as raw materials.
In this work, inexpensive and commercially available
nickel is used as a catalyst. In addition, inexpensive and
stable aryl sulfamates are used as electrophiles. Moreover,
the nickel catalyst can be recycled three times.
Keywords: 2-Aryl-benzothiazoles, Aryl sulfamates, Coup-
ling reaction
Introduction
2-Aryl-benzothiazoles are an important class of nitrogen-
containing heterocyclic compounds, which are present in Results and discussion
numerous natural products and synthetic compounds.
Due to their biological and pharmacological properties, Initially, the reaction of benzothiophene and p-toluenesul-
2-aryl-benzothiazoles exhibit a wide range of biological fonate was used to evaluate the catalytic activity of various
activities, including insecticidal [1], antifungal [2], nema- nickel compounds (0.2 equivalent) using 1,10-phen·H2O
ticidal [3], weed killing [2, 3], and plant growth regulation (1,10-phenanthroline·H2O) as a co-catalyst. As listed
activities in agriculture[3]. In medicine, these compounds in Table 1, the results showed that NiBr2(DME) (DME =
exhibit anti-tumor [4-7] and anti-bacterial activity [8, 9], 1,2-dimethoxyethane) exhibited the best catalytic activity
and are also used in the treatment of Alzheimer’s disease with 68% yield (Table 1, entry 4). When the co-catalyst
[10, 11]. Therefore, these compounds have received sustai- was changed to an amino acid the reaction yielded little
ned attention from researchers in organic synthesis.
or no product. This means that NiBr2 with 1,10-phen is a
Theconventionalmethodusedtoprepare2-aryl-benzo- highly active catalyst. Moreover, it was easier to generate
thiazoles involves reacting 2-aminothiophenol with benzyl NiBr2 with 1,10-phen ligands by replacing DME with 1,10-
alcohol [12], benzylamine [13-16], benzonitrile [12, 17, 18] phen, rather than directly from 1,10-phen and NiBr2. The
or aromatic aldehyde [19-27]. However, this approach is yield was increased to 92% by increasing the amount of
NiBr2(DME) to 40 mol% (Table 1, entry 9).
After completion of the reaction, the reaction mixture
was filtered, and the starting material and product were
washed with diethyl ether. The catalyst residue was then
charged with lithium t-butoxide, along with a small
amount of 1,10-phenanthroline and used in the reaction
again Repeated use of the catalyst showed that it was
active for three cycles (table 1, entry 14-16).
* Corresponding author: Xiaofeng Yu, School of Materials
and Chemical Engineering, Bengbu University, Bengbu, Anhui
233030, P. R. China, e-mail: feiyu@mail.ustc.edu.cn
Renyuan Song, Liping Gou and Guangrong Wang, School of
Materials and Chemical Engineering, Bengbu University, Bengbu,
Anhui 233030, P. R. China
Zhen Zhang, College of Pharmacy and Biological Engineering,
Chengdu University, Sichuan 610106, P. R. China
Open Access. © 2020 Yu et al., published by De Gruyter.ꢀ
Attribution alone 4.0 License.
ꢀThis work is licensed under the Creative Commons
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X. Yu et al.: Synthesis of 2-aryl-benzothiazoles via Ni-catalyzed coupling of benzothiazoles and aryl sulfamates
Table 1. Synthesis of 2-(p-CH3Ph)benzothiazoles by benzothiazoles
Table 2. Synthesis of 2-arylbenzothiazoles from benzothiazoles with
a,b
a,b
with p-CH3PhOSO2NMe2
ArOSO2NMe2
S
S
[Ni],Ligand
S
S
N
NiBr2(DME)
p-CH3PhOSO2NMe2
tBuOLi, dioxane
ArOSO2NMe2
Ar
N
1,10-phen.H2O
N
N
S
N
Entry
Catalyst (mol%)
Ligand (mol%)
Yield/%
S
N
S
N
CF3
N
1
2
3
4
5
6
7
8
NiBr2⋅6H2O (20)
NiBr2 (20)
1,10-phen⋅H2O(20)
1,10-phen⋅H2O(20)
1,10-phen⋅H2O(20)
1,10-phen⋅H2O(20)
1,10-phen⋅H2O(20)
1,10-phen⋅H2O(20)
1,10-phen(20)
51
50
NRc
68
10
45
31
81
b 85%
c 95%
f 91%
a 92%
d 89%
g 90%
Ni(COD)2 (20)e
NiBr2(DME) (20)d
Ni(acac)2(20)f
O
O
S
S
N
S
O
N
N
NiCl2⋅6H2O (20)
NiBr2(DME) (20)
NiBr2(DME) (30)
e 93%
S
N
S
N
1,10-phen⋅H2O(30)
S
Cl
9
NiBr2(DME) (40)
NiBr2(DME) (20)
NiBr2(DME) (20)
NiBr2(DME) (20)
NiBr2(DME) (20)
NiBr2(DME) (40)f
NiBr2(DME) (40)g
NiBr2(DME) (40)h
1,10-phen⋅H2O(40)
-
92
N
10
11
12
13
14
15
16
NRc
tracec
NRc
tracec
90
h 96%
i 94%
L-proline
L-lysine
a) Reaction conditions: benzothiazoles (0.1 mmol ), ArOSO2NMe2
(0.1 mmol ), tBuOLi(0.2 mmol ),1,10-phen⋅H2O(0.04 mmol ),
NiBr2(DME)(0.04 mmol ), dioxane (3 ml), 120 oC, N2 atmosphere.
b) Isolated yields.
L-valine
1,10-phen⋅H2O(40)
1,10-phen⋅H2O(40)
1,10-phen⋅H2O(40)
89
85
a) Reaction conditions: benzothiazoles (0.1 mmol ), p-CH3PhO-
SO2NMe2 (0.1 mmol ), tBuOLi(0.2 mmol ), 1,10-phen⋅H2O, NiBr2(DME),
dioxane (3 ml), 120 oC, N2 atmosphere. b) Isolated yields. c) By
1H NMR. d) DME = 1,2-dimethoxyethane. e) COD = 1,5-Cyclooctadiene.
f) acac = acetylacetone. f) First recovered catalyst. g) Second
recovered catalyst. h) Third recovered catalyst.
to prepare a variety of 2-aryl-benzothiazole compounds.
The aryl group in the aryl sulfamate starting material can
contain electron-withdrawing groups (such as -C6H4CF3,
-C6H4OCH3, and -C6H4Cl), electron-donating groups (such
as -C6H4CH3, and -C6H4N(CH3)2), or large conjugated rings
(such as -C10H7). This method avoids the use of unstable
and highly toxic 2-aminothiophenol, highly expensive
palladium catalysts, and unstable aromatic iodine or aro-
matic aldehydes as starting materials. In future work, sub-
stituted benzothiazole compounds will be studied as raw
materials.
A wide variety of aryl sulfamates and benzothiazoles
were investigated with regard to the effect on the yield
of their corresponding 2-aryl-benzothiazole compounds.
Table 2 shows that the reaction of various aryl sulfamates
gave the desired products in high yield. The product yields
obtained using aryl sulfamates bearing electron-dona-
ting groups were higher than those containing electron- Experimental
withdrawing groups [p-N(CH3)2PhOSO2NMe2 (95%),
p-CF3PhOSO2NMe2 (85%)]. Sterically hindered aryl sul- General procedure for the synthesis of
famates gave higher product yields; the yield obtained 2-aryl-benzothiazole
using o-CH3OPhOSO2NMe2 is higher than its correspon-
ding m- and p-derivatives. The product yield obtained A Schlenk tube was charged with the benzothiazole
using aryl sulfamates containing a naphthalene ring was (0.10 mmol) and aryl sulfamate (0.10 mmol) [31], follo-
the highest. This was attributed to the positively charged wed by lithium t-butoxide (0.20 mmol), nickel catalyst
intermediate being stabilized by the electron-donating (0.4 equivalent), and co-catalyst (0.4 equivalent). The
groups and large conjugated ring.
nitrogen atmosphere was replaced three times and 3 mL
of dioxane was introduced to the reaction mixture. The
Schlenk tube was placed into an oil bath and the reaction
mixture was stirred at 120°C for 12 h. The reaction mixture
was extracted with Et2O. The combined organic phases
Conclusions
An inexpensive, reusable and commercially available were dried with anhydrous Na2SO4, filtered, concentra-
nickel catalyst can be used to efficiently catalyze the coup- ted under vacuum and the resulting residue purified by
ling reaction between benzothiazoles and aryl sulfamates column chromatography on silica gel.
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Catalyst recovery experiment
6.75 (d, J = 8.7 Hz, 2H), 3.00 (s, 6H). 13C NMR (100 MHz,
CDCl3) δ 168.0, 158.7, 155.3, 136.5, 130.1, 127.4, 125.4, 123.5,
After completion of the catalytic reaction, the reaction 120.1, 118.2, 110.3, 39.5. HRMS (EI): m/z [M]+ calcd for
mixture was filtered and the filter cake was washed three C15H11N2S: 254.09; found: 254.11.
times with diethyl ether. The powder solid was charged
with two equivalents of lithium t-butoxide and 0.4 equiva- 2-(3-Methoxyphenyl) benzothiazole (d) [21, 35]
lents of 1,10-phenanthroline and was used in the reaction
O
again (table 1, entry 14-16).
S
N
Characterization Data of the Products:
White solid; 89% yield; mp 88–90°C. IR (KBr): 3061, 2855,
2-p-Tolyl-benzothiazole (a) [17, 21, 32]
1630, 1510, 1340, 887, 750, 711, 681 cm–1. 1H NMR (400 MHz,
CDCl3): δ = 8.23 (d, J = 8.0, 1 H), 7.90 (d, J = 7.8 Hz, 1 H), 7.54
(t, J = 7.4, Hz, 1 H), 7.49 (d, J = 7.5, Hz, 1 H), 7.17 (t, J = 7.5, Hz,
1 H), 7.15-7.11 (m, 2 H), 6.96 (d, J = 7.4 Hz, 1 H), 3.55 (s, 3 H).
13C NMR (100 MHz, CDCl3): δ = 160.1, 156.1, 152.9, 125.2,
120.5, 116.1, 123.9, 122.5, 119.6, 117.4, 109.3, 106.1, 101.2, 51.1.
HRMS (EI): m/z [M]+ calcd for C14H11NOS: 241.06; found:
241.09.
S
N
Yellow solid; 92% yield; mp 87–89°C. IR (KBr): 3081, 2957,
1449, 1431, 965, 840,758, 450 cm–1. H NMR (400 MHz,
1
CDCl3): δ = 8.06 (d, J = 8.0 Hz, 1 H), 7.98 (d, J = 7.9 Hz, 2 H),
7.88(d, J=8.0Hz, 1H), 7.47(t, J=7.6Hz, 1H), 7.36(t, J=8.2Hz,
1 H), 7.28 (t, J = 8.5 Hz, 2 H), 2.40 (s, 3 H). 13C NMR (100
MHz, CDCl3): δ = 168.1, 154.1, 141.2, 135.0, 131.1, 130.0, 127.4,
126.3, 125.3, 123.2, 121.4, 21.6. HRMS (EI): m/z [M]+ calcd for
C14H11NS: 225.06; found: 225.09.
2-(2-Methoxyphenyl) benzothiazole (e) [21]
O
S
N
2-[4-(Trifluoromethyl)phenyl]-benzothiazole (b) [17, 33]
White solid; 93% yield; mp 110–112°C. IR (KBr): 3055, 2850,
S
1
1628, 1520, 1361, 755, 723 cm–1. H NMR (400 MHz, CDCl3):
CF3
N
δ = 8.45 (d, J = 7.9, 1 H), 7.91 (d, J = 8.0 Hz, 1 H), 7.54 (t,
J = 7.9 Hz, 1 H), 7.49 (d, J = 7.9 Hz, 1 H), 7.17 (t, J = 7.5, Hz, 1 H),
7.14-7.11 (m, 2 H), 7.06 (d, J = 7.4 Hz, 1 H), 6.96 (d, J = 7.9 Hz,
1 H), 3.45 (s, 3 H). 13C NMR (100 MHz, CDCl3): δ = 161.1, 155.1,
153.9, 135.1, 131.1, 125.2, 124.9, 122.5, 120.5, 118.3, 108.8,
105.2, 103.1, 52.8. HRMS (EI): m/z [M]+ calcd for C14H11NOS:
241.06; found: 241.11.
White solid; 85% yield; mp 160–163°C. IR (KBr): 3044,
1630, 1454, 1425, 1073, 976, 840, 761, 624, 450 cm–1. 1H NMR
(400 MHz, CDCl3): δ = 8.20 (d, J = 7.9 Hz, 2 H), 8.10 (d, J = 7.9
Hz, 1 H), 7.91 (d, J = 7.9 Hz, 1 H), 7.74 (d, J = 7.9 Hz, 2 H), 7.50
(t, J = 7.9 Hz, 1 H), 7.43 (t, J = 7.9 Hz, 1 H). 13C NMR (100 MHz,
CDCl3) δ 165.8, 154.3, 135.9, 134.1, 130.3 (q, J = 31.3 Hz),
125.5, 126.5, 125.4 (q, J = 3.5 Hz), 122.9 (q, J = 270.9 Hz), 122.1,
120.0. HRMS (EI): m/z [M]+ calcd for C14H8F3NS: 279.03;
found: 279.08.
2-(4-Methoxyphenyl)benzothiazole (f) [17, 35]
S
O
N
2-[4-(N, N-dimethyl)phenyl]-benzothiazole (c) [17, 34]
White solid; 91% yield; mp 123–125°C. IR (KBr): 3045,
S
N
N
1
2848, 1558, 1432, 1356, 1311, 1110, 748, 725. H NMR (400
MHz, CDCl3) δ = 8.14-8.11 (m, 3H), 7.65 (d, J = 7.9 Hz, 1H),
7.50 (t, J = 7.3 Hz, 1H), 7.38 (t, J = 7.5 Hz, 1H), 7.09 (d, J =
White solid; 95% yield; mp 167–169°C. IR (KBr): 3088, 8.6 Hz, 2H), 3.45 (s, 3H). 13C NMR (100 MHz, CDCl3) δ 165.9,
1
2880, 1450, 1309, 1233, 1050, 965, 749, 715, 415. H NMR 159.7, 151.2, 130.5, 128.9, 124.3, 121.5, 120.4, 119.6, 117.8,
(400 MHz, CDCl3): δ = 7.96 (t, J = 7.5 Hz, 3H), 7.89 (d, 113.2, 53.4. HRMS (EI): m/z [M]+ calcd for C14H11NOS: 241.06;
J = 7.8 Hz, 1H), 7.50 (t, J = 7.5 Hz, 1H), 7.38 (t, J = 7.4 Hz, 1H), found: 241.09.
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X. Yu et al.: Synthesis of 2-aryl-benzothiazoles via Ni-catalyzed coupling of benzothiazoles and aryl sulfamates
2-(4-Chlorophenyl)benzothiazole (g) [17, 34]
startup for high-level talents (BBXY2018KYQD20) and
the Natural Science Foundation of Bengbu University
(2017GJPY06). This research was supported by the Anhui
Provincial Engineering Laboratory of Silicon-based Mate-
rials, and the Separation and Purification Technology
S
Cl
N
White solid; 90% yield; mp 116–118°C. IR (KBr): 3048, Research Center of Bengbu University.
1
2915, 1573, 1438, 1316, 1120, 759, 743. H NMR (400 MHz,
CDCl3) δ = 8.19 (d, J = 8.1 Hz, 1H), 8.11 (d, J = 8.4 Hz, 2H),
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8.4 Hz, 2H), 7.38 (d, J = 8.0 Hz, 1H). 13C NMR (100 MHz,
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White solid; 96% yield; mp 128–130°C. IR (KBr): 3056,
2860, 1530, 1443, 1358, 1200, 1101, 1005, 958, 850, 751,
731 cm–1.1 H NMR (400 MHz, CDCl3): δ = 8.94 (d, J = 7.8 Hz,
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J = 7.8 Hz, 2 H), 7.63 (t, J = 7.8 Hz, 1 H), 7.60-7.58 (m, 3 H), 7.41
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S
N
White solid; 94% yield; mp 126–128 °C. IR (KBr): 3055,
2890, 1502, 1435, 1360, 1205, 998, 899, 758, 723. H NMR
1
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(400 MHz, CDCl3) δ 8.56 (s, 1H), 8.25 (d, J = 8.5 Hz, 1H), 8.10
(d, J = 8.0 Hz, 1H), 7.96-7.91 (m, 4H), 7.54-7.51 (m, 3H), 7.26
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136.2, 135.2, 131.0, 129.8, 128.0, 127.6, 126.6, 125.8, 123.1,
122.7, 122.0, 121.3, 120.5, 119.9, 119.0. HRMS (EI): m/z [M]+
calcd for C17H11NS: 261.06; found: 261.08.
Acknowledgements: Financial support was received from
the Natural Science Foundation of the Higher Education
InstitutionsofAnhuiProvince(KJ2019A0856, KJ2017A573),
Bengbu University funded project of scientific research
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X. Yu et al.: Synthesis of 2-aryl-benzothiazoles via Ni-catalyzed coupling of benzothiazoles and aryl sulfamatesꢁ
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