Trans-3,5-dihydroperoxy-3,5-dimethyl-1,2-dioxalane/HBr system as new, effective, mild and non-toxic reagent for synthesis of 2-aryl-1H-benzothiazoles and 2-aryl-1-arylmethyl-1H-benzimidazoles

Article abstract of DOI:10.1002/jccs.201100568

Ttrans-3,5-dihydroperoxy-3,5-dimethyl-1,2-dioxalane has been used as new, effective, solid, inexpensive and nontoxic oxidant for in situ generation of Br⁺ from HBr. This system has been applied as catalyst for synthesis of 2-aryl-1H-benzothiazo

Full text of DOI:10.1002/jccs.201100568

JOURNAL OF THE CHINESE
CHEMICAL SOCIETY
Note
Trans-3,5-dihydroperoxy-3,5-dimethyl-1,2-dioxalane/HBr System as New, Effective,
Mild and Non-toxic Reagent for Synthesis of 2-Aryl-1H-benzothiazoles and
2-Aryl-1-arylmethyl-1H-benzimidazoles
Kaveh Khosravia* and Samira Kazemib
aDepartment of Chemistry, Faculty of Science, University of Arak, Zip Cod 38156-879 Arak, Iran
bDepartment of Chemistry, Shahr-e-Rey Branch, Islamicazad University, Tehran, Iran
(Received: Sept. 23, 2011; Accepted: Nov. 28, 2011; Published Online: Dec. 12, 2011; DOI: 10.1002/jccs.201100568)
Ttrans-3,5-dihydroperoxy-3,5-dimethyl-1,2-dioxalane has been used as new, effective, solid, inexpensive
and nontoxic oxidant for in situ generation of Br+ from HBr. This system has been applied as catalyst for
synthesis of 2-aryl-1H-benzothiazoles and 2-aryl-1-arylmethyl-1H-benzimidazoles at room temperature
in excellent yields and high purity.
Keywords: Ttrans-3,5-dihydroperoxy-3,5-dimethyl-1,2-dioxalane; 2-Aryl-1H-benzothiazoles;
2-Aryl-1-arylmethyl-1H-benzimidazoles; HBr.
INTRODUCTION
2-Substituted benzothiazoles are an important class
tant. On the other hand, the best method for preparation of
benzimidazoles is condensation of 1,2-phenylenediamine
with aldehydes. In recent years, several Lewis acids such as
Sc(OTf)3,13 Yb(OTf)3,14 In(OTf)3,15 oxalic acid,16 proline,17
H2O2/HCl,18 p-toluensulfonic acid-silica gel,19 Caro’s
acid-silica gel,20 acetic acid/MW,21 H2O2/CAN,22 ambelite
IR-120,23 K10,24 oxone,25 iodine,26 SiO2/ZnCl2,27 and
SSA.28 Recently, gem-dihydroperoxides have been used as
new and effective oxidant.29 Therefore, now, we have syn-
thesized trans-3,5-dihydroperoxy-3,5-dimethyl-1,2-diox-
alane as new, solid and powerful oxidant for oxidation re-
actions.30 In this work, for in situ generation of Br+, we
have used trans-3,5-dihydroperoxy-3,5-dimethyl-1,2-di-
oxalane/HBr system. Br+ as a powerful and effective Lewis
acid has catalyzed the synthesis of benzothiazoles (Scheme
I) and benzimidazoles (Scheme II). Although, in synthesis
of benzimidazoles, tow products may be obtained, in this
procedure, 2-aryl-1-arylmethyl-1H-benzimidazoles were
obtained as only product (Scheme II).
of compounds in medicinal and industrial chemistry.1 Also,
compounds with containing benzimidazoles core have
been shown a wide range of biological properties.2 Due to
for importance of benzothiazoles, for synthesis of these
compounds several methodologies have been reported.3
Two major methods have been reported: 1. Condensation
of 2-aminothiophenol with aldehydes. 2. Cyclization of
thiobenzanilides.4
Several reagents have been used for catalyzes of this
condensation that include DMSO/120 °C,5a ionic liquid
1-phenyl-3-methylimidazoliumbromide ([pmIm]Br),5b
scandium triflate,5c silicagel,5d MnO2/SiO2,5e molecular io-
dine,5f molecular oxygen promoted by activated carbon,5g
p-TSOH,5h SiO2/graphite,5i electrochemical synthesis in
methanol containing sodium acetate as supporting electro-
lyte,5j water/110 °C,5k carboxylic acid,6 acid chlorides7 or
esters.8
Also, several sundry methods such as micro wave
–mediated reaction of 2-aminothiophenol with b-chloro-
cinnamadehydes,9 palladium-catalyzed Suzuki biaryl cou-
pling of 2-bromobenzothiazoles with aryl bromides,10 cou-
pling of benzothiazoles with aryl bromides11 and reaction
of thiophenol with aromatic nitriles12 have been used. Un-
fortunately, many of these procedures suffer from several
defects such as using toxic and/or inexpensive catalysts,3,4
the use of hazardous and carcinogenic organic solvent and
multistep process for reaction.5 So, founding of optimized
methodology for synthesis of benzothiazoles is still impor-
Scheme I Synthesis of 2-arylbenzothiazoles
RESULTS AND DISCUSSION
For optimization test, benzaldehyde has been reacted
with 2-aminothiophenol in different solvents. After optimi-
* Corresponding author. Tel: +98(0861)2777400; Fax: +98(0861)2774031; E-mail: khosravi.kaveh@gmail.com
J. Chin. Chem. Soc. 2012, 59, 557-560
© 2012 The Chemical Society Located in Taipei & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
557

Note
Khosravi and Kazemi
Yield (%)a
Synthesis of 2-aryl-1-arylmethylbenzimi-
dazoles
Table 1. Selection of best solvent
Scheme II
Entry
Solvent
Time (min)
1
2
3
4
5
EtOH
CHCl3
MeCN
CCl4
25
65
22
70
25
85
69
91
52
87
THF
zation tests, MeCN has choose as the best solvent (Table 1,
91% yield, 22 minutes).
Table 2. Synthesis of 2-aryl-1H-benzothiazoles in optimized
This procedure is simple, effective, clean and non-
toxic. The products were obtained in high yields (Table 2,
3). Also, products were obtained by aqua work-up in good
purity. Thus, complex purification methods were not nec-
essary.
condition
m. p (°C)
Time Yield
(min) (%)b
Producta
Ar
found
Reported55
2a
2b
2c
2d
2e
2f
C6H5
22
21
23
91
86
87
83
85
83
85
82
81
82
84
87
85
86
77
112-114
87-89
110-112
85-87
4-MeC6H5
2-MeC6H5
In this work, we have used trans-3,5-dihydroperoxy-
3,5-dimethyl-1,2-dioxalane as new, powerful and solid ox-
idant to in situ generation Br+ as a powerful Lewis acid to
activation of carbonyl group. The suggested mechanism
was shown in Scheme III.
50-52
52-54
2- MeOC6H5 30
4- MeOC6H5 25
100-102
120-122
84-86
99-102
119-121
81-83
2-ClC6H5
4-ClC6H5
2-OHC6H5
4-OHC6H5
2-NO2C6H5
3-NO2C6H5
4-BrC6H5
4-FC6H5
30
23
26
30
23
22
22
24
25
40
2g
2h
2i
118-119
124-126
230-232
132-134
182-184
130-132
96-98
116-117
122-124
227-228
133-135
182-184
129-131
98-100
165-166
100-103
2j
Scheme III Suggested mechanism
2k
2l
2m
2n
2o
4-CNC6H5
2-Furyl
166-168
102-104
a The products were characterized by their physical properties
and spectral analysis and compared with authentic samples.
b Isolated yields.
Table 3. Synthesis of 2-aryl-1-arylmethyl-1H-benzimidazoles in
optimized conditions
m.p (°C)
Time Yield
Entry
Ar
(min)
(%)
found
Reported45
As shown in Tables 2 and 3, both aldehydes with elec-
tron-withdrawing and electron-relaxing groups were re-
acted in this method in short times.
3a
3b
3c
3d
3e
3f
C6H5
29
45
38
40
42
36
52
47
43
44
40
35
50
92
88
83
80
80
84
75
78
80
83
83
90
76
130-132
128-130
132-134
153-155
157-159
140-142
203-205
247-249
170-172
120-122
190-192
254-256
98-100
132-134
126-128
130-131
154-155
158-159
138-140
205-208
250-253
169-170
119-120
190-191
254-256
96-98
4-MeC6H5
4-MeOC6H5
2- MeOC6H5
2-ClC6H5
CONCLUSION
4-ClC6H5
In summary, we have developed a facile and efficient
method for synthesis of benzothiazoles and 2-aryl-1-aryl-
methyl-1H-benzimidazoles using trans-3,5-dihydroper-
oxy-3,5-dimethyl-1,2-dioxalane/HBr system. The advan-
tages of this method include (i) short reaction times, (ii)
high yields, (iii) easy work-up, (iv) using a little amount
of reagent, and (v) avoid of using of molecular bromine.
Applying this system is easy, available, clean and effec-
tive.
3g
3h
3i
2-OHC6H5
4-OHC6H5
2-NO2C6H5
4-NO2C6H5
4-CNC6H5
4-N(Me)2C6H5
2-furyl
3j
3k
3l
3m
a The products were characterized by their physical properties
and spectral analysis and compared with authentic samples.
b Isolated yields.
558
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Synthesis of 2-Aryl-1-arylmethylbenzimidazoles
EXPERIMENTAL
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We are grateful to the Department of Chemistry, Fac-
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J. Chin. Chem. Soc. 2012, 59, 557-560