Copper promoted C-S and C-N cross-coupling Reactions:The synthesis of 2-(N-Aryolamino)benzothiazoles and 2-(N-Aryolamino)benzimidazoles

Article abstract of DOI:10.1016/j.tet.2019.05.006

The synthesis of 2-(N-aryolamino)benzothiazoles and 2-(N-aryolamino)benzimidazoles has been accomplished in the presence of copper catalyst. These reactions involve C-S and C-N cross-coupling reaction. All electron donating and withdrawing substituent's readily underwent the reaction to give target products in good to excellent yield. In addition, the reaction also gave target product in high yield with bulk scale.

Full text of DOI:10.1016/j.tet.2019.05.006

Accepted Manuscript
Copper promoted C-S and C-N cross-coupling Reactions:The synthesis of 2-(N-
Aryolamino)benzothiazoles and 2-(N-Aryolamino)benzimidazoles
Baji vali Shaik, Mohan Seelam, Ramana Tamminana, Prasad Rao Kammela
PII:
S0040-4020(19)30513-7
https://doi.org/10.1016/j.tet.2019.05.006
TET 30327
DOI:
Reference:
To appear in: Tetrahedron
Received Date: 11 April 2019
Accepted Date: 2 May 2019
Please cite this article as: Shaik Bv, Seelam M, Tamminana R, Kammela PR, Copper promoted C-
S and C-N cross-coupling Reactions:The synthesis of 2-(N-Aryolamino)benzothiazoles and 2-(N-
Aryolamino)benzimidazoles, Tetrahedron (2019), doi: https://doi.org/10.1016/j.tet.2019.05.006.
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ACCEPTED MANUSCRIPT
R1
O
H
N
H
CuSO4.5H2O (10 mol %) or Cu(OAc)2.H2O (10 mol %)
1,10-Phenanthroline (20 mol %), DMSO, Cs2CO3 (1.0 eq),
100 °C or 120 °C, 14 h
N
N
R
R
N
X
O
H
R1
X
I
R, R1 = EDG & EWG
X = S, NH
36 examples
Yield 60-99%
EDG-Electron Donating Group
EWG-Electron Withdrawing Group
GRAPHICAL ABSTRACT
Graphical abstract synopsis: Multistep reaction has been developed for the synthesis of
substituted 2-(N-Aryolamino)benzothiazoles and 2-(N-Aryolamino)benzimidazoles under
moderate reaction conditions.

ACCEPTED MANUSCRIPT
Copper Promoted C-S and C-N Cross-Coupling Reactions:The
Synthesis of 2-(N-Aryolamino)benzothiazoles and 2-(N-
Aryolamino)benzimidazoles
Baji vali Shaik,b Mohan Seelam,a Ramana Tamminana,c and Prasad Rao Kammela*a
a
Prasad Rao Kammela, Department of Chemistry, Bapatla Engineering College, Bapatla,
Guntur, AP- 522101, India
Baji Vali Shaik, Department of Chemistry, Gudlavalleru Engineering College,
b
Gudlavalleru, Krishna, AP, Indi
Ramana Tamminana, Department of Chemistry, GITAM University, NH-207,
c
Doddaballapur Taluk, Bengaluru District, Karnataka-561203
E-mail: prasad17467@gmail.com,
ORCID ID: orcid.org/0000-0003-1987-9222
ABSTRACT
The synthesis of 2-(N-aryolamino)benzothiazoles and 2-(N-aryolamino)benzimidazoles
has been accomplished in the presence of copper catalyst. These reactions involve C-S and C-
N cross-coupling reaction. All electron donating and withdrawing substituent’s readily
underwent the reaction to give target products in good to excellent yield. In addition, the
reaction also gave target product in high yield with bulk scale.
KEYWORDS
ꢀ 2-(N-Aryolamino)benzothiazoles
ꢀ 2-(N-Aryolamino)benzimidazoles
ꢀ Copper catalyst
ꢀ C-S and C-N Cross-coupling reaction
ꢀ Mild reaction conditions

ACCEPTED MANUSCRIPT
1. Introduction
In recent decades, the formation of powerful carbon-heteroatom bonds has been developed
through cross-coupling reactions using transition-metal.1 Among these, carbon-nitrogen and
carbon-sulphur bond formation has received much attention due to the presence of this
moiety in many molecules that are of biological, pharmaceutical, and material interest.2
Especially, benzimidazoles and benzothiazoles are very important benzofused compounds
because of their applications in therapeutic,3 and biological sciences (Figure 1).4
CH3
O
HN
N
S
O
H3C
OH
NH
O
N
N
N
S
N
O
H
N
O
H
NO2
Antimicrobial Activity
or
Analgesic Activity
Antitumour agent
O
NH2
N
OMe
N
H
N
N
N
OH
N
H
F
Astemizole
NU 1085
Antihistamine drug
Antagonist and Inhibitor
Fig 1: Examples of biological active compounds
Thus the synthesis of benzothiazole and benzimidazoles have been developed by traditional
methods,5 and using various transition metals like Cu,6 Pd,7 Ru,8 Fe,9 Co,10 Zn,11 and some of
them have developed under metal free conditions.12 However, very less reports are available
for the synthesis of 2-(N-Aroylamino)benzothiazoles and benzimidazoles using transition
metal. For example, Pan and co-workers13 have accomplished method for the synthesis of 2-
(N-aroylamino) benzothiazoles using copper. However, they have used different from our
ligand. Later on, Yadav et al,14 have reported using brominating reagent under strong acidic
conditions. In addition, other researchers4g-j have also accomplished for the construction of 2-
(N-aroylamino) benzothiazoles. Whereas, no report is available for the synthesis of 2-(N-
aroylamino)benzimidazoles. Therefore, in view of the above observation which is slightly
complex, herein, we demonstrate simple and general method for the synthesis of 2-(N-
Benzoylamino) benzothiazoles through C-S cross-coupling reaction and similarly, we also
would like to report for the construction of 2-(N-Benzoylamino) benzimidazoles through C-N
cross-coupling reaction using cheap, readily available, non-toxic and air stable copper source
as catalyst under mild reaction conditions.

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2. Materials and methods
2.1 General information: Aniline, CS2, CuSO4·5H2O (98%), CuI (98%), CuBr (98%), Cu2O
(97%), CuBr2 (99%), CuCl2·2H2O (99%) and Cu(OAc)2·H2O (98%), K2CO3, KOH,
K3PO4·3H2O and Cs2CO3 were purchased from Aldrich and used without further purification.
The solvents were purchased and dried according to standard procedure prior to use. 1H NMR
(400 MHz) spectra were recorded with a Varian 400 spectrometer. Infrared (IR) spectra
recorded on a Perkin Elmer Spectrum one FT-IR spectrometer. Elemental analyses were
recorded with Perkin Elmer CHNS analyzer.
2.2. General Procedure for the synthesis of 2-(N-aroylamino)benzothiazole:
To a stirred mixture of DMSO (2 ml), N-(2-iodophenyl)-N’-benzoyl thiourea (1 mmol) was
added slowly and the reaction mixture stirred for several minutes at room temperature. To
that previous reaction mixture K2CO3 (138 mg, 1 mmol), CuSO4.5H2O (10 mol %, 16 mg)
o
and 1,10-phenonthroline (20 mol %, 36 mg) were added and stirred at 100 C for 14 h.
Progress of the reaction was monitored by TLC using ethyl acetate and hexane (2:8). After
finish the reaction, the reaction mixture was cooled to room temperature. Then, the solution
was washed with ethyl acetate (7 ml) and water (3 mL) for 5 times. The organic layer was
evoparated and crude reaction mixture was purified by by silica gel (60-120 mesh) column
chromatography using ethylacetate in hexane as eluent to obtain final product 2-(N-
13
aroylamino)benzothiozole which was characterized by NMR (1H and C), IR and elemental
analysis.
2.3 General Procedure for the synthesis of 2-(N-aroylamino)benzimidazole:
To a stirred mixture of DMSO (2 ml), N-(2-iodophenyl)-N’-benzoyl guanidine (1 mmol) was
added slowly and the reaction mixture stirred for several minutes at room temperature. To
that previous reaction mixture Cs2CO3 (325 mg, 1 mmol), Cu(OAc)2.H2O (10 mol %, 18.1
o
mg) and 1,10-phenonthroline (20 mol %, 36 mg) were added and stirred at 120 C for 14 h.
Progress of the reaction was monitored by TLC using ethyl acetate and hexane (2:8). After
finish the reaction, the reaction mixture was cooled to room temperature. Then, the solution
was washed with ethyl acetate (7 ml) and water (3 mL) for 5 times. The organic layer was
evoparated and crude reaction mixture was purified by by silica gel (60-120 mesh) column
chromatography using ethylacetate in hexane as eluent to obtain final product 2-(N-
aroylamino)benzimidazole which was characterized by NMR (1H and 13C), IR and elemental
analysis.

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3. Results and discussions
Synthesis of 2-(N-benzoyl)benzothiazoles: The starting materials were prepared using our
recent reported procedure (Scheme 1).15 This reaction proceeds via nucleiophilic
substitution/addition. Soon after the end of the preparation of starting material, the
optimization of reaction conditions was carried out using N-(2-iodophenyl)-N’-benzoyl
thiourea as model substrate with various solvents, different copper sources, and bases at 100
°C (Table 1). Initially, we tried the reaction with CuI as catalyst in the absence of ligand and
fortunately the reaction gave target product 2a in 10% yield (Table 1, entry 1). Taking
advantage of this result, later, we have checked various ligands, among them ligand L4 gave
desired product 2a in complete conversion (Table 1, entry 5). In contrast, other ligands L1-
L3 gave final product in less to moderate yield (Table 1, entries 2-4). The reaction with bases
like, K2CO3 and Cs2CO3 to provide target product 2a in quantitative yield are used. In contrast,
bases such as KOH, K3PO4·3H2O were less effective in providing desired product (Table 1,
entries 6& 7). In set of solvents, DMSO and DMF gave desired product 2a in complete
conversation. Whereas, other solvents like THF, Toluene, CH3CN were shown less activity to
give target product. Both copper (I) and copper (II) species (CuI, CuBr, CuCl, CuSO4.5H2O
and Cu(OAc)2.H2O) have been exhibited similar catalytic activity (Table 1, entries 13-16).
Lowering the catalyst amount (5 mol %) and base (0.5 eq) led to S-arylation to afford the
cyclised expected product 2a in less conversion (Table 1, entries 17-18). The control
experiment confirmed that no target product could be obtained in the absence of catalyst and
ligand (Table 1, entry 19).
I
NH2
O
S
O
O
N
N
KSCN or NH4SCN
DMF, 80 °C, 1 h
NCS
I
Cl
H
H
DMF, 80 °C, 1 h
1a
Scheme 1: The synthetic route for the synthesis of N-benzoyl-N’-(2-iodophenyl) thiourea
Encouraged by these results, we further pursued the scope of the process with respect to other
substrates. The substrates 1b, 1c, 1d and 1e having electron donating substituents like 4-Me,
4-OMe, 2-Me and 2,4-DiMe were carried out under optimized reaction condition to afford
respective target products 2b, 2c, 2d and 2e in high yield. The substrates 1f, 1g hold weak
electron withdrawing substituents readily underwent the reaction to obtain cyclised products
2f, 2g in good yield, whereas, the substrates 1h, 1i bearing strong electron withdrawing
groups proceeded the reaction to provide respective desired products 2h, 2i in moderate yield.
On the other hand the cyclisation of the substrates 1j, 1k, 1l, 1m & 1n having 4-Me, 4-OMe,

ACCEPTED MANUSCRIPT
2,4-DiMe, 4-Cl & 4-F proceeded to give desired products 2j, 2k, 2l, 2m & 2n in 66-94%
yield.
Table 1: Optimization for the synthesis of N-Benzoyl benzothiazole
O
I
O
S
S
Solvent, Copper source (10 mol %)
N
base (1 eq), ligand (20 mol %), 100 °C, 14 h
H
N
N
H
N
H
1a
2a
H2N
NH2
HN
Me
NH HO
Me
OH
N
N
L4
L1
L3
L2
Entry
Solvent
Copper source
Base
Ligand
Conversionb
2a
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMF
1
2
3
4
5
6
7
8
CuI
CuI
CuI
CuI
CuI
CuI
CuI
CuI
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
KOH
K3PO4·3H2O
Cs2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
10
30
45
20
100
45
65
100
100
60
-
L1
L2
L3
L4
L4
L4
L4
L4
L4
L4
L4
L4
L4
L4
L4
L4
L4
-
9
CuI
CuI
CuI
THF
10
11
12
13
14
15
16
17c
18d
Toluene
CH3CN
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
30
CuI
CuBr
CuCl
CuSO4·5H2O
Cu(OAc)2·H2O
CuSO4·5H2O
CuSO4·5H2O
-
89
100
100
100
100
54
42
19
n.d.
a
Reaction conditions: N-(2-iodophenyl)-N’-benzoyl thiourea (1 mmol), solvent (2 mL), catalyst (10 mol %),
b
ligand (20 mol %), base (1 mmol), 14 h, 100 °C. Conversion based on diagnostic peaks integration in
1H NMR of crude reaction mixture. CuSO4·5H2O (5 mol %) used. K2CO3 (0.5 equiv) used. n.d. = not
c
d
detected.

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Table 2: Substrate scope for the synthesis of 2-(N-Benzyol) benzothiazolesa
O
I
S
N
O
S
CuSO4.5H2O (10 mol %),
1,10-Phenanthroline (20 mol %)
DMSO, Cs2CO3 (1.0 eq), 100 °C, 14 h
N
H
R
N
N
H
H
2a-i
R = EDG & EWG
1a-i
Entry
1
Substrate (R)
Product
Yield (%)b
O
O
I
O
S
S
N
99
H
N
N
N
H
H
2a
1a
I
Me
Me
S
N
O
S
98
H
N
N
N
H
I
2
3
H
1b
2b
OMe
MeO
O
O
O
S
S
N
N
N
96
92
H
N
H
H
2c
1c
S
N
I
O
S
H
N
N
H
N
H
4
Me
Me
Me
Me
O
2d
1d
Me
S
I
Me
Cl
O
O
S
N
87
H
N
N
N
H
5
6
H
2e
1e
S
O
O
I
Cl
F
S
N
H
N
80
82
68
N
H
N
H
2f
1f
I
F
S
N
O
O
O
S
H
N
N
H
N
H
7
2g
1g
O
O
I
CN
NC
S
N
S
H
N
N
N
H
H
8
9
1h
S
2h
I
S
N
65
N
N
H
H
N
H
NO2
2i
1i
NO2
a
Reaction conditions: Substituted N-(2-iodophenyl)-N’-benzoyl thiourea (1 mmol), DMSO (2 mL),
b
CuSO4·5H2O (10 mol %), 1,10-phennanthroline (20 mol %), K2CO3 (1 mmol), 14 h, 100 °C. Isolated yield. c
CuSO4·5H2O (5 mol %) used. d K2CO3 (0.5 equiv) used. n.d. = not detected.

ACCEPTED MANUSCRIPT
Table 3: Substrate scope for the synthesis of N-Benzyol benzothiazolesa
O
I
S
N
O
S
CuSO4.5H2O (10 mol %),
1,10-Phenanthroline (20 mol %)
DMSO, Cs2CO3 (1.0 eq), 100 °C, 14 h
N
H
N
N
R
2j-n
R = EDG & EWG
R
H
H
1j-n
Entry
Substrate (R)
Product
Yield (%)b
O
I
O
O
S
S
N
N
H
1
2
94
96
N
H
N
H
Me
2j
1j
O
Me
I
S
N
S
N
H
N
H
1k
N
H
OMe
2k
O
Me
MeO
S
I
Me
O
O
S
S
N
H
N
N
H
1l
N
H
I
89
74
Me
Cl
3
4
Me
O
O
O
O
2l
Me
Cl
S
N
N
H
N
H
N
H
2m
1m
I
S
N
O
O
O
S
N
H
N
H
N
H
5
6
F
66
65
F
2n
1n
I
S
N
S
N
H
N
H
1o
N
H
CN
2o
NC
I
S
N
S
N
H
N
H
N
H
7
COOCH3
60
60
H3COOC
2p
1p
O
O
I
S
N
O
O
S
S
N
H
N
H
1q
N
H
8
NO2
CF3
2q
O2N
I
S
N
N
H
N
H
N
H
9
62
F3C
2r
1r
a
Reaction conditions: Substituted N-(2-iodophenyl)-N’-benzoyl thiourea (1 mmol), DMSO (2 mL),
b
CuSO4·5H2O (10 mol %), 1,10-phennanthroline (20 mol %), K2CO3 (1 mmol), 14 h, 100 °C. Isolated yield. c
CuSO4·5H2O (5 mol %) used. d K2CO3 (0.5 equiv) used. n.d. = not detected.

ACCEPTED MANUSCRIPT
Finally, we have also examined reactivity of N-(2-halophenyl)-N’-benzoyl thiourea under
optimized reaction conditions. The reaction with N-(2-bromophenyl)-N’-benzoyl thiourea
were used to provide a target product 2a in 59% yield (eq 1). In contrast, no target product
could be occurred in case of N-(2-chlorophenyl)-N’-benzoyl thiourea under optimized
reaction conditions (eq 2).
Br
O
O
S
S
N
CuSO4.5H2O (10 mol %),
1,10-Phenanthroline (20 mol %)
DMSO, Cs2CO3 (1.0 eq), 100 °C, 14 h
N
eq 1
eq 2
N
H
N
H
H
2a, Yield 59%
Cl
O
O
S
S
N
CuSO4.5H2O (10 mol %),
1,10-Phenanthroline (20 mol %)
DMSO, Cs2CO3 (1.0 eq), 100 °C, 14 h
N
H
N
H
N
H
no reaction
In order to explain the practical usage of this method, the reaction of N-(2-iodophenyl)-N’-
benzoyl thiourea was examined 1a with 10 mmol scale. Very fortunately the reaction could
give their respective target products in good yield (Scheme 3).
I
O
O
S
S
N
CuSO4.5H2O (10 mol %),
1,10-Phenanthroline (20 mol %)
DMSO, Cs2CO3 (1.0 eq), 100 °C, 14 h
N
N
N
H
H
H
1a
10 mmol
2a, 82% yield
Scheme 2: Large Scale Construction of 2-(N-Benzoyl) benzothiazole
Synthesis of 2-(N-benzoyl)benzimidazoles: Firstly, we prepared the starting precursor using
our recent reported procedure (Scheme 2).15 Using the above reaction conditions of the
formation of 2-(N-benzyol)benzothiazole, the construction of 2-(N-benzyol)benzimidazole
was studied. It was found that the target product have been obtained at 120 °C using all
copper sources (10 mol %), 1,10-phenanthrolene (20 mol %), Cs2CO3 as base in the presence
of DMSO solvent.
O
H
H
N
H
ClI. NH SCN (1 eq), DMSO
N
N
4
N
III. CuSO4.5H2O (50 mol%),
Et3N (1 eq), NH3, rt, 2 h
80 °C, 1 h
NH2
O
O
NH2
S
I
I
II.
80 °C, 1 h
I
Scheme 3: Pathway for the synthesis of N-benzoyl-N’-(2-iodophenyl) guanidine
In response to this encourage results, we used a range of substituted 2-(N-
benzoyl)benzimidazoles to investigate the scope and limits of this reaction. As we shown in
Table 4, both electron rich and electron withdrawing substituents can provide the

ACCEPTED MANUSCRIPT
corresponding benzimidazoles in modearate to good yield. The substrates 3b, 3c, 3d and 3e
having electron donating substituents like 4-Me, 4-OMe, 2-Me and 2,4-DiMe carried out
Table 4: Substrate scope for the synthesis of 2-(N-Benzyol) benzimidazolesa
O
H
N
H
N
Cu(OAc)2.H2O (10 mol %),
1,10-Phenanthroline (20 mol %)
DMSO, Cs2CO3 (1.0 eq), 120 °C, 14 h
N
N
H
N
O
R
NH2
3a-i
4a-i
I
R
R = EDG & EWG
Entry
Substrate (R)
Product
Yield (%)b
O
H
N
H
N
N
N
93
1
2
H
N
O
NH2
I
4a
3a
H
O
O
H
N
Me
MeO
Me
N
N
N
H
95
O
O
N
NH2
Me
I
4b
H
3b
H
N
N
N
N
H
96
88
3
4
N
NH2
MeO
Me
I
4c
O
O
3c
H
N
H
N
N
N
H
N
O
Me
Me
NH2
Me
I
4d
H
N
3d
Me
H
N
N
N
H
87
76
5
6
N
O
O
O
NH2
Me
Cl
F
I
Me
O
O
O
O
4e
3e
H
N
H
Cl
F
N
N
N
H
4f
N
NH2
I
3f
H
N
H
N
N
N
H
4g
7
8
72
64
NH2
N
I
3g
H
H
N
NC
N
N
N
H
O
O
N
NH2
NC
I
4h
3h
H
NO2
H
N
N
N
N
H
60
9
N
NH2
I
4i
NO2
3i
a
Reaction conditions: Substituted N-(2-iodophenyl)-N’-benzoyl guanidine (1 mmol), DMSO (2 mL),
b
Cu(OAc)2·H2O (10 mol %), 1,10-phenanthroline (20 mol %), Cs2CO3 (1 mmol), 14 h, 120 °C.
Isolated yield. n.d. = not detected.
under optimized reaction condition to afford respective target products 4b, 4c, 4d and 4e in
high yield. The substrates 3f, 3g bearing weak electron withdrawing substituents readily

ACCEPTED MANUSCRIPT
underwent the reaction to obtain domino products 4f, 4g in good yield, whereas, the
substrates 3h, 3i bearing strong electron withdrawing groups proceeded the reaction to
Table 5: Substrate scope for the synthesis of N-Benzyol benzimidazolesa
O
H
N
H
N
Cu(OAc)2.H2O (10 mol %),
1,10-Phenanthroline (20 mol %)
DMSO, Cs2CO3 (1.0 eq), 120 °C, 14 h
N
N
H
R
R
N
O
NH2
3j-r
4j-r
Me
I
R = EDG & EWG
Yield (%)b
Entry
Substrate (R)
Product
O
Me
H
N
H
N
N
N
H
N
Me
OMe
1
2
Me
91
O
NH2
4j
O
O
H
N
Me
Me
I
3j
H
N
N
N
H
N
93
93
Me
C2H5
O
OMe
C2H5
NH2
H
4k
I
N
3k
N
H
N
H
N
N
Me
C3H7
3
4
5
4l
O
O
O
H
N
NH2
Me
Me
I
3l
H
N
N
H
N
N
Me
C3H7
Me
93
4m
O
Me
H
N
NH2
Me
I
3m
N
H
H
N
N
N
Me
89
71
4n
O
Me
NH2
3n
O
O
H
N
Cl
F
Me
Me
Me
I
H
N
N
H
N
N
Me
Me
4o
Cl
F
6
7
O
O
H
N
NH2
I
3o
N
H
H
N
N
N
4p
70
65
O
O
H
N
NH2
3p
I
CN
N
H
H
N
N
Me
Me
N
CN
4q
H
N
8
9
O
O
NH2
NO2
Me
Me
I
3q
N
H
H
N
N
N
NO2
4r
62
NH2
I
3r
a
Reaction conditions: Substituted 4-Me-N-(2-iodophenyl)-N’-benzoyl guanidine (1 mmol), DMSO (2 mL),
Cu(OAc)2·H2O (10 mol %), 1,10-phennanthroline (20 mol %), Cs2CO3 (1 mmol), 14 h, 120 °C. n.d. = not
detected.
provide respective desired products 4h, 4i in moderate yield. On the other hand, the
substrates 3j, 3k, 3l & 3m having para substituted electron donating groups 4-Me, 4-OMe, 4-
Et, 4-iPr proceeded to give desired products 4j, 4k, 4l & 4m in 92-93% yield. Whereas

ACCEPTED MANUSCRIPT
phenyl ring bearing electron withdrawing groups like 4-Cl, 4-F, 4-CN & 4-NO2 to afford
their corresponding target products 4o, 4p, 4q & 4r in moderate yield. The phenyl ring holds
disubstituted group 2, 4-diMe to obtain final product 4n in 89% yield.
To reveal the practical utility of the protocol, N-(2-iodophenyl)-N’-benzoyl guanidine 3a was
tested with 10 mmol scale under optimized reaction conditions and the reaction gave
expected product 4a in 75% yield (Scheme 3).
O
H
N
Cu(OAc)2.H2O (10 mol %),
1,10-Phenanthroline (20 mol %)
DMSO, Cs2CO3 (1.0 eq), 120 °C, 14 h
H
N
N
N
H
N
O
NH2
4a, 75% yield
I
3a
10 mmol
Scheme 4: Bulk Scale Synthesis of 2-(N-Benzoyl) benzothiazole
Similarly, the reactivity of N-(2-halophenyl)-N’-benzoyl guanidine was also tested. In this
connection, moderate yield was obtained in case of N-(2-bromophenyl)-N’-benzoyl guanidine
(eq. 3), whereas, N-(2-chlorophenyl)-N’-benzoyl guanidine didn’t give expected C-N cross-
coupled product under optimized reaction conditions (eq. 4).
O
H
N
Cu(OAc)2.H2O (10 mol %),
1,10-Phenanthroline (20 mol %)
DMSO, Cs2CO3 (1.0 eq), 120 °C, 14 h
H
N
N
N
eq 3
eq 4
H
N
O
NH2
Br
4a, Yield 45%
O
H
N
Cu(OAc)2.H2O (10 mol %),
1,10-Phenanthroline (20 mol %)
DMSO, Cs2CO3 (1.0 eq), 120 °C, 14 h
H
N
N
N
H
N
O
NH2
no reaction
Cl
To reveal the mechanism in more details the catalyst was extracted after finish the reaction.
The isolated catalyst was subjected to Powder XRD analyses (Figure 2). The spectrum shows
the peaks corresponding to 2θ = 73.65, 61.53, 42.45, 36.12, 29.59. The peaks are very close
to that given by JCPDS data of XRD for copper (I) species.16 No other diffraction peaks have

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Fig 2: XRD of Cu (I) species
been appeared in the XRD pattern. Therefore, we believe that Cu(I) species have formed in the
reaction medium. In addition, a radical inhibition test was carried out for checking the radical
path mechanism. As result shown in the Table 6, the yield of the reaction was not changed
when TEMPO (radical scavenger) was added to the reaction mixture. This result strongly
believes that the reaction may not proceed via radical mechanism and it undergoes via
oxidative-reductive mechanism.
Table 6. Effects of Radical Inhibitor on the Synthesis of Substituted N-Benzyol
benzimidazoles a
O
H
N
H
N
Optimized Conditions
N
N
H
O
N
NH2
I
3a
4a
Entry
Radical Scavenger
4a (%)
1
2b
-
92
93
TEMPO
a
Reaction conditions: Substituted N-(2-iodophenyl)-N’-benzoyl guanidine (1 mmol), DMSO
(2 mL), Cu(OAc)2·H2O (10 mol %), 1,10-phenanthroline (20 mol %), Cs2CO3 (1 mmol), 14
h, 120 °C. b TEMPO (0.5 mmol) used.
O
CuII
+e
CuI
X
I
N
O
X
H
N
2a or 4a
N
N
H
H
1a or 3a
oxidative
addition
reductive
elimination
X = S, NH
H
N
H
H
N
N
N
C
C
X
O
X
O
Cu
I
Cu
b
a
H:B + I-
:B

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Scheme 5: Proposed catalytic cycle for the synthesis of 2-(N-Benzoyl)benzothiazole and
2-(N-Benzoyl)benzimidazole.
Based on the experimental evidence the reaction pathway is proposed in the Scheme 5. The
copper (I) species undergoes oxidative addition with thiourea or guanidine to yield copper
(III) intermediate a, which can complete the catalytic cycle by reductive elimination to afford
the target product 2a or 4a using base via intermediate b. The above results and proposed
mechanism clearly suggest that the reported methodology involves intra molecular C-S17 and
C-N18 cross-coupling reaction.
4. Conclusion
In summary we have developed simple and new route for the synthesis of 2-(N-
Benzoyl)benzothiazole and 2-(N-Benzoyl)benzimidazole under mild reaction conditions.
Cheap, readily available and air stable copper source as catalyst was used for this
methodology. This method involves intra molecular C-S and C-N cross-coupling technique.
All the substrates were found to give their corresponding target products in good to excellent
yields.
Acknowledgments
The authors thankful to Department of Chemistry, Gudlavalleru Engineering College,
Gudlavalleru for providing work space and the authors grateful thanks to Icon Pharmaceutical
Lab for providing instrumental support.
Conflicts of interest
The authors declare that there are no conflicts of interest
.
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Highlights
ꢀ To the best of our knowledge no one has reported for the synthesis
of substituted 2-(N-Aryolamino)benzimidazoles in the presence of
copper catalyst.
ꢀ This methodology is general, clean and efficient.
ꢀ We could find cheap, readily available and air stable copper
catalyst for desulphurization.
ꢀ The reactions are rapid, facile and accomplished at room
temperature.
ꢀ Moreover, all substituents readily underwent the reaction to
provide their corresponding target products in good to high yield.