A practical synthesis of 2-aminobenzothiazoles via the tandem reactions of 2-haloanilines with isothiocyanates catalyzed by immobilization of copper in MCM-41

Article abstract of DOI:10.1016/j.jorganchem.2012.01.014

The heterogeneous tandem reactions of 2-haloanilines with isothiocyanates were achieved in DMSO using Et₃N as base at 80 °C in the presence of a 3-(2-aminoethylamino)propyl-functionalized MCM-41-immobilized copper(II) complex [MCM-41-2N-CuSO₄], yielding a variety of 2- aminobenzothiazoles in good to excellent yields. This heterogeneous copper catalyst exhibited higher activity than CuSO₄ and can be recovered and recycled by a simple filtration of the reaction solution and used for at least 10 consecutive trials without any decreases in activity.

Full text of DOI:10.1016/j.jorganchem.2012.01.014

Journal of Organometallic Chemistry 705 (2012) 44e50
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
A practical synthesis of 2-aminobenzothiazoles via the tandem reactions
of 2-haloanilines with isothiocyanates catalyzed by immobilization of copper
in MCM-41
1
1
1
*
Ruian Xiao , Wenyan Hao , Jinting Ai , Ming-Zhong Cai
Department of Chemistry, Jiangxi Normal University, Nanchang, Jiangxi Province 330022, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
The heterogeneous tandem reactions of 2-haloanilines with isothiocyanates were achieved in DMSO
using Et3N as base at 80 ꢀC in the presence of a 3-(2-aminoethylamino)propyl-functionalized MCM-41-
immobilized copper(II) complex [MCM-41-2N-CuSO4], yielding a variety of 2-aminobenzothiazoles in
good to excellent yields. This heterogeneous copper catalyst exhibited higher activity than CuSO4 and can
be recovered and recycled by a simple filtration of the reaction solution and used for at least 10
consecutive trials without any decreases in activity.
Received 6 November 2011
Received in revised form
12 January 2012
Accepted 17 January 2012
Keywords:
Ó 2012 Elsevier B.V. All rights reserved.
Immobilized copper catalyst
2-Aminobenzothiazole
Tandem reaction
Functionalized MCM-41
Heterogeneous catalysis
1. Introduction
2-halobenzenamines and isothiocyanates using the CuI (10 mol
%)/1,10-phenanthroline (20 mol%) catalytic system to prepare 2-
2-Aminobenzothiazoles, one of the important classes of
heterocyclic compounds, are broadly found in biological chemistry
aminobenzothiazoles [10]; Li and Ding’s groups reported iron-
catalyzed tandem reactions of 2-halobenzenamines and iso-
thiocyanates leading to 2-aminobenzothiazoles [13,14]. Meanwhile,
the ligand-free copper-catalyzed tandem reactions of 2-
halobenzenamines and isothiocyanates were also reported [15,16].
Although these transition-metal-catalyzed tandem reactions of
2-halobenzenamines and isothiocyanates are highly efficient for
the synthesis of 2-aminobenzothiazoles, the problem with homo-
geneous catalysis is the difficulty to separate the catalyst from the
reaction mixture and the impossibility to reuse it in consecutive
reactions. In addition, homogeneous catalysis might result in
unacceptable metal contamination of the desired isolated product,
which is a particularly significant drawback for its application in the
pharmaceutical industry. In contrast, heterogeneous catalysts can
be easily separated from the reaction mixture by a simple filtration
of the reaction solution and reused in successive reactions provided
that the active sites have not become deactivated. Heterogeneous
catalysis also helps to minimize wastes derived from reaction
workup, contributing to the development of green chemical
processes [17e20]. From industrial and environmental points of
view, the development of a cheap, efficient and environmentally
benign catalyst is challenging and important. In an ideal system,
they can be recovered by simple filtration and reused infinitely, and
contamination of products by the metal is prevented.
and medicinal areas [1e3].
A
great amount of 2-
anilinobenzothiazoles derivatives are proven to be anticancer
active and the 2-aminobenzothiazole moieties are privileged
pharmacophores as well as valuable reactive intermediates [4e10].
Therefore, considerable effort has been made in the development of
efficient strategies for their construction. The majority of efficient
methods include the palladium- or copper-catalyzed intra-
molecular cyclization of 2-bromobenzothioureas [8,11,12]. Castillon
and coworkers reported Pd-catalyzed cyclization of 2-
bromophenylthioamides using the Pd2(dba)3/(2-biphenyl)P(t-Bu)2
catalytic system [11]. However, both a ligand and a base are
required to promote the reaction, and the substrates are not readily
available. Recently, the transition-metal-catalyzed tandem reac-
tions of 2-halobenzenamines and isothiocyanates for the synthesis
of 2-aminobenzothiazoles have received considerable attention
because of their efficiency and low costs. For example, Wu and
coworkers described a copper-catalyzed tandem reaction between
* Corresponding author. Tel.: þ86 791 88120388; fax: þ86 791 88120388.
E-mail address: caimzhong@163.com (M.-Z. Cai).
1
Fax: þ86 791 8812 0388.
0022-328X/$ e see front matter Ó 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2012.01.014

R. Xiao et al. / Journal of Organometallic Chemistry 705 (2012) 44e50
45
Polymer-supported palladium complexes catalysts have success-
fully been used in variety of carbonecarbon bond or
a suspension of 2.2 g of the MCM-41 in 180 mL of dry toluene. The
mixture was stirred for 24 h at 100 ꢀC. Then the solid was filtered
and washed by CHCl3 (2 ꢂ 20 mL), and dried in vacuum at 160 ꢀC
for 5 h. The dried white solid was then soaked in a solution of 3.1 g
of Me3SiCl in 100 mL of dry toluene at room temperature under
stirring for 24 h. Then the solid was filtered, washed with acetone
(3 ꢂ 20 mL) and diethyl ether (3 ꢂ 20 mL), and dried in vacuum at
120 ꢀC for 5 h to obtain 3.49 g of hybrid material MCM-41-2N. The
nitrogen content was found to be 1.84 mmol/g by elemental
analysis.
a
carboneheteroatom bond formation reactions [20e23], however,
polymer-supported copper complexes catalysts for organic trans-
formations have received less attention [24,25]. Recently, Yang
and coworkers reported the reaction of 2-haloanilines with iso-
thiocyanates catalyzed by Merrifield resin-supported phenan
throlineeCu(I) complex for the synthesis of 2-aminobenzothiazoles.
However, the preparation of this heterogeneous copper catalyst
required use of expensive and unavailable 5-amine-1,10-
phenanthrolin and the catalytic activity decreased gradually with
repeated uses [26]. Therefore, the development of new and easily
accessible heterogeneous copper catalysts having a high activity and
good stability is a topic of enormous importance. Our approach was
guided by three imperatives: the polymeric ligand should be easily
accessible (1), starting from readily available and cheap reagents (2).
Thepolymericcoppercatalystshouldbeairstable, whichshouldallow
its storage in normal bottles with unlimited shelf life (3). Develop-
ments on the mesoporous material MCM-41 provided a new possible
candidate for a solid support for immobilization of homogeneous
catalysts [27]. MCM-41 has a regular pore diameter of ca. 5 nm and
a specific surface area >700 m2 gꢁ1 [28]. Its large pore size allows
passage of large molecules such as organic reactants and metal
complexes through the pores to reach to the surface of the channel
[29e31]. To date, some palladium and rhodium complexes on func-
tionalized MCM-41 support have beenprepared and successfully used
in organicreactions [32e38]. However, noimmobilizationofcopperin
MCM-41 has been described in the open literature. It is generally
believed that high surface area of heterogeneous catalyst results in
high catalytic activity. Considering the fact that MCM-41 support has
an extremely high surface area and the catalytic copper species
is anchored on the inner surface of the mesopore of MCM-41, we
expect that MCM-41-supported copper catalyst will exhibit high
activity and good reusability. In continuing our efforts to develop
greener synthetic pathways for organic transformations, our new
approach, described in this paper, was to design and synthesize a new
3-(2-aminoethylamino)propyl-functionalized MCM-41-immobilized
copper complex (MCM-41-2N-CuSO4), which was used as an effec-
tive copper catalyst for the tandem reactions of 2-halobenzenamines
and isothiocyanates leading to 2-aminobenzothiazoles.
2.2.2. Preparation of MCM-41-2N-CuSO4
In a small Schlenk tube, 1.28 g of the above-functionalized
MCM-41 (MCM-41-2N) was mixed with 0.106 g (0.66 mmol) of
CuSO4 in 10 mL of dry DMF. The mixture was stirred at room
temperature for 7 h under an argon atmosphere. The solid product
was filtered by suction, washed with DMF, distilled water and
acetone and dried at 40 ꢀC/26.7 Pa under Ar for 5 h to give 1.323 g of
a pale blue copper complex (MCM-41-2N-CuSO4). The nitrogen,
sulfur and copper content were found to be 1.70 mmol/g,
0.45 mmol/g and 0.43 mmol/g, respectively.
2.3. General procedure for the synthesis of 2-aminobenzothiazoles
A mixture of 2-halobenzenamine (1.0 mmol), isothiocyanate
(1.2 mmol),
Et3N
(2.0 mmol)
and
MCM-41-2N-CuSO4
(0.0025 mmol) in DMSO (2 mL) was stirred under an air atmo-
sphere at 80 ꢀC for 5e24 h. After completion of the reaction as
indicated by TLC, the mixture was cooled to room temperature. The
solution was diluted with ethyl acetate (30 mL ) and filtered. The
catalyst was washed with ethyl acetate (2 ꢂ 5 mL) and Et2O
(2 ꢂ 5 mL) and reused in the next run. The organic layer was
washed with water (2 ꢂ10 mL) and dried over anhydrous Na2SO4.
After evaporating under vacuum, the residue was purified by flash
chromatography on silica gel (petroleum/ethyl acetate ¼ 10:1 to
4:1) to provide the corresponding pure product 3.
2.3.1. N-Phenylbenzo[d]thiazol-2-amine, 3a
White solid, mp 162e164 ꢀC (lit [15]. mp 161e164 ꢀC). 1H NMR
(400 MHz, DMSO-d6):
d
¼ 10.59 (s, 1H), 7.91 (d, J ¼ 7.2 Hz, 2H), 7.83
(d, J ¼ 7.2 Hz, 1H), 7.69 (d, J ¼ 7.2 Hz, 1H), 7.44e7.35 (m, 3H), 7.19 (t,
2. Experimental
J ¼ 6.4 Hz, 1H), 7.07 (t, J ¼ 6.4 Hz, 1H) ppm. 13C NMR (100 MHz,
DMSO-d6):
121.5, 119.7, 118.3 ppm.
d
¼ 162.1, 152.7, 141.2, 130.5, 129.5, 126.3, 122.7, 122.5,
2.1. General remarks
All chemicals were reagent grade and used as purchased. All
solvents were dried and distilled before use. The products were
purified by flash chromatography on silica gel. IR spectra were
determined on a PerkineElmer 683 instrument. 1H NMR spectra
were recorded on a Bruker Avance (400 MHz) spectrometer with
TMS as an internal standard in CDCl3 as solvent. 13C NMR spectra
were recorded on a Bruker Avance (100 MHz) spectrometer in
CDCl3 as solvent. Melting points are uncorrected. Copper content
was determined with inductively coupled plasma atom emission
Atomscan16 (ICP-AES, TJA Corporation). X-ray powder diffraction
was obtained on Damx-rA (Rigaka). Microanalyses were measured
by using a Yanaco MT-3 CHN microelemental analyzer. The meso-
porous material MCM-41 was easily prepared according to a liter-
ature procedure [39].
2.3.2. N-(p-Tolyl)benzo[d]thiazol-2-amine, 3b
White solid, mp 178e179 ꢀC (lit [15]. mp 178e179 ꢀC). 1H NMR
(400 MHz, DMSO-d6):
d
¼ 10.42 (s, 1H), 7.79 (d, J ¼ 8.0 Hz, 1H), 7.71
(d, J ¼ 8.4 Hz, 2H), 7.61 (d, J ¼ 8.0 Hz, 1H), 7.32 (t, J ¼ 7.6 Hz, 1H), 7.17
(d, J ¼ 8.0 Hz, 2H), 7.13 (t, J ¼ 7.6 Hz, 1H), 2.27 (s, 3H) ppm. 13C NMR
(100 MHz, DMSO-d6):
d
¼ 162.2, 152.7, 138.7, 131.5, 130.4, 129.8,
126.3, 122.6, 121.4, 119.5, 118.4, 20.9 ppm.
2.3.3. N-(4-Methoxyphenyl)benzo[d]thiazol-2-amine, 3c
White solid, mp 152e154 ꢀC (lit [13]. mp 154e155 ꢀC). 1H NMR
(400 MHz, DMSO-d6):
d
¼ 10.35 (s, 1H), 7.78e7.73 (m, 3H), 7.60 (d,
J ¼ 8.0 Hz, 1H), 7.31 (t, J ¼ 7.6 Hz, 1H), 7.12 (t, J ¼ 7.4 Hz, 1H), 6.97 (d,
J ¼ 8.8 Hz, 2H), 3.74 (s, 3H) ppm. 13C NMR (100 MHz, DMSO-d6):
d
¼ 162.6, 155.2, 152.8, 134.5, 130.5, 126.3, 122.4, 121.4, 120.2, 119.4,
114.7, 55.6 ppm.
2.2. Preparation of the catalyst
2.3.4. N-(4-Fluorophenyl)benzo[d]thiazol-2-amine, 3d
2.2.1. Preparation of MCM-41-2N
White solid, mp 215e216 ꢀC (lit [40]. mp 216e217 ꢀC). 1H NMR
A
solution of 1.54 g of 3-(2-aminoethylamino)propyl-
(400 MHz, DMSO-d6):
J ¼ 8.0 Hz, 1H), 7.62 (d, J ¼ 8.0 Hz, 1H), 7.32 (t, J ¼ 7.8 Hz, 1H),
d
¼ 10.55 (s, 1H), 7.88e7.83 (m, 2H), 7.79 (d,
trimethoxysilane in 18 mL of dry chloroform was added to

46
R. Xiao et al. / Journal of Organometallic Chemistry 705 (2012) 44e50
2
7.26e7.12 (m, 3H) ppm. 13C NMR (100 MHz, DMSO-d6):
d
¼ 162.1,
3JCF ¼ 4.0 Hz), 122.6 (q, JCF ¼ 32.0 Hz), 119.6, 119.2, 118.7 (q,
1
157.8 (d, JCF ¼ 237.0 Hz), 152.5, 137.6, 130.5, 126.3, 122.7, 121.5,
3JCF ¼ 4.0 Hz) ppm.
119.9, 119.7 (d, 3JCF ¼ 16.0 Hz), 116.0 (d, 2JCF ¼ 23 Hz) ppm.
2.3.12. N-(4-Nitrophenyl)-6-(trifluoromethyl)benzo[d]thiazol-2-
amine, 3l
2.3.5. N-(4-Chlorophenyl)benzo[d]thiazol-2-amine, 3e
White solid, mp 204e206 ꢀC (lit [13]. mp 206e207 ꢀC). 1H NMR
Yellow solid, mp 250e252 ꢀC (lit [14]. mp 253e254 ꢀC). 1H NMR
(400 MHz, DMSO-d6):
d
¼ 10.68 (s, 1H), 7.88 (d, J ¼ 8.8 Hz, 2H), 7.84
(400 MHz, DMSO-d6):
d
¼ 11.38 (s, 1H), 8.33 (s, 1H), 8.25 (d,
(d, J ¼ 8.0 Hz, 1H), 7.66 (d, J ¼ 7.6 Hz, 1H), 7.44 (d, J ¼ 8.8 Hz, 2H),
J ¼ 7.2 Hz, 2H), 8.00 (d, J ¼ 7.2 Hz, 2H), 7.82 (d, J ¼ 7.2 Hz, 1H), 7.66
7.36 (t, J ¼ 7.6 Hz, 1H), 7.20 (t, J ¼ 7.6 Hz, 1H) ppm. 13C NMR
(d, J ¼ 7.2 Hz, 1H) ppm. 13C NMR (100 MHz, DMSO-d6):
d
¼ 164.1,
3
(100 MHz, DMSO-d6):
d
¼ 161.8, 152.4, 140.0, 130.5, 129.3, 126.4,
154.7, 146.3, 141.8, 131.5, 125.7 (q, JCF ¼ 8.0 Hz), 125.0 (q,
1JCF ¼ 272.0 Hz),123.8 (q, 2JCF ¼ 33.0 Hz),123.5,120.5,119.6,118.0 (q,
3JCF ¼ 7.0 Hz) ppm.
125.9, 123.0, 121.6, 119.8, 119.7 ppm.
2.3.6. N-(4-Nitrophenyl)benzo[d]thiazol-2-amine, 3f
Orange solid, mp 225e226 ꢀC (lit [13]. mp 225e227 ꢀC). 1H NMR
2.3.13. N-Phenyl-6-chlorobenzo[d]thiazol-2-amine, 3m
(400 MHz, DMSO-d6):
d
¼ 11.24 (s, 1H), 8.28 (d, J ¼ 9.2 Hz, 2H), 8.02
White solid, mp 187e189 ꢀC (lit [13]. mp188e189 ꢀC). 1H NMR
(d, J ¼ 8.8 Hz, 2H), 7.90 (d, J ¼ 7.6 Hz,1H), 7.72 (d, J ¼ 7.8 Hz,1H), 7.41
(400 MHz, DMSO-d6):
d
¼ 10.56 (s, 1H), 7.92 (s, 1H), 7.78 (d,
(t, J ¼ 7.8 Hz, 1H), 7.26 (t, J ¼ 7.6 Hz, 1H) ppm. 13C NMR (100 MHz,
J ¼ 8.0 Hz, 2H), 7.58 (d, J ¼ 8.0 Hz, 1H), 7.38 (d, J ¼ 8.0 Hz, 1H),
DMSO-d6):
121.8, 120.5, 117.6 ppm.
d
¼ 161.1, 151.9, 146.9, 141.3, 130.8, 126.6, 125.9, 123.7,
7.35e7.32 (m, 2H), 7.04 (t, J ¼ 7.2 Hz, 1H) ppm. 13C NMR (100 MHz,
DMSO-d6):
121.2, 120.6, 118.4 ppm.
d
¼ 162.7, 151.5, 140.9, 132.2, 129.5, 126.6, 126.5, 122.8,
2.3.7. N-Cyclohexylbenzo[d]thiazol-2-amine, 3g
Pale oil [41]. 1H NMR (400 MHz, DMSO-d6):
d
¼ 7.92 (d,
2.3.14. N-(p-Tolyl)-6-chlorobenzo[d]thiazol-2-amine, 3n
J ¼ 7.6 Hz, 1H), 7.63 (d, J ¼ 7.2 Hz, 1H), 7.37 (d, J ¼ 7.6 Hz, 1H),
7.22e7.17 (m, 1H), 7.01e6.96 (m, 1H), 3.72e3.68 (m, 1H), 2.00e1.97
(m, 2H), 1.74e1.71 (m, 2H), 1.60e1.56 (m, 1H), 1.40e1.14 (m, 5H)
White solid, mp 197e198 ꢀC (lit [13]. mp 198e200 ꢀC). 1H NMR
(400 MHz, DMSO-d6):
d
¼ 10.46 (s, 1H), 7.91 (s, 1H), 7.66 (d,
J ¼ 7.6 Hz, 2H), 7.56 (d, J ¼ 8.4 Hz,1H), 7.32 (d, J ¼ 8.4 Hz,1H), 7.17 (d,
ppm. 13C NMR (100 MHz, DMSO-d6):
121.2, 121.1, 118.3, 53.2, 32.8, 25.7, 24.9 ppm.
d
¼ 165.6, 153.2, 130.6, 125.9,
J ¼ 7.6 Hz, 2H), 2.28 (s, 3H) ppm. 13C NMR (100 MHz, DMSO-d6):
d
¼ 162.9, 151.6, 138.4, 132.1, 131.8, 129.9, 126.5, 126.4, 121.2, 120.4,
118.6, 20.9 ppm.
2.3.8. N-Phenyl-6-(trifluoromethyl)benzo[d]thiazol-2-amine, 3h
White solid, mp 160e161 ꢀC (lit [41]. mp 163e165 ꢀC). 1H NMR
2.3.15. N-(4-Methoxyphenyl)-6-chlorobenzo[d]thiazol-2-amine, 3o
White solid, mp 185e187 ꢀC. 1H NMR (400 MHz, DMSO-d6):
(400 MHz, DMSO-d6):
d
¼ 10.72 (s, 1H), 8.19 (s, 1H), 7.78 (d,
J ¼ 8.0 Hz, 2H), 7.67 (d, J ¼ 8.0 Hz,1H), 7.54 (d, J ¼ 8.4 Hz,1H), 7.33 (t,
d
¼ 10.28 (s, 1H), 7.80 (s, 1H), 7.57 (d, J ¼ 8.8 Hz, 2H), 7.43 (d,
J ¼ 8.4 Hz, 1H), 7.22 (d, J ¼ 8.4 Hz, 1H), 6.87 (d, J ¼ 8.8 Hz, 2H), 3.66
(s, 3H) ppm. 13C NMR (100 MHz, DMSO-d6):
J ¼ 7.8 Hz, 2H), 7.00 (t, J ¼ 7.2 Hz, 1H) ppm. 13C NMR (100 MHz,
DMSO-d6):
d
¼ 164.4, 155.0, 140.2, 130.7, 129.0, 124.6 (q,
d
¼ 162.8, 154.9, 151.2,
1JCF ¼ 270.0 Hz), 122.7 (q, 3JCF ¼ 3.0 Hz), 122.6, 122.4 (q,
133.7, 131.6, 125.9, 125.7, 120.6, 119.9, 119.7, 114.2, 55.2 ppm. Anal.
Calcd. for C14H11N2SOCl: C, 57.82; H, 3.81. Found: C, 57.59; H, 3.67.
3
2JCF ¼ 33.0 Hz), 119.0, 118.6 (q, JCF ¼ 4.0 Hz), 118.3 ppm.
2.3.9. N-(4-Methoxyphenyl)-6-(trifluoromethyl)benzo[d]thiazol-2-
amine, 3i
2.3.16. N-(4-Fluorophenyl)-6-chlorobenzo[d]thiazol-2-amine, 3p
White solid, mp 213e214 ꢀC. 1H NMR (400 MHz, DMSO-d6):
White solid, mp 200e201 ꢀC (lit [41]. mp 200e202 ꢀC). 1H NMR
d
¼ 10.63 (s, 1H), 7.99 (s, 1H), 7.91e7.82 (m, 2H), 7.62 (d, J ¼ 8.0 Hz,
(400 MHz, DMSO-d6):
d
¼ 10.63 (s, 1H), 8.25 (s, 1H), 7.74 (d,
1H), 7.39 (d, J ¼ 8.0 Hz, 1H), 7.27 (t, J ¼ 8.6 Hz, 2H) ppm. 13C NMR
J ¼ 8.8 Hz, 2H), 7.70 (d, J ¼ 8.8 Hz, 1H), 7.62 (d, J ¼ 8.4 Hz, 1H), 7.01
(100 MHz, DMSO-d6):
d
¼ 162.3, 157.4 (d, 1J ¼ 237.0 Hz), 150.9,
CF
(d, J ¼ 8.8 Hz, 2H), 3.79 (s, 3H) ppm. 13C NMR (100 MHz, DMSO-d6):
136.8, 131.7, 126.1, 121.4, 120.8, 120.1, 119.6 (d, 3J ¼ 7.0 Hz), 115.5
CF
1
2
d
¼ 165.5, 155.7, 133.9, 131.1, 125.2 (q, JCF ¼ 270.0 Hz), 123.2 (q,
(d, JCF ¼ 22.0 Hz) ppm. Anal. Calcd. for C13H8N2FSCl: C, 56.01; H,
3JCF ¼ 4.0 Hz), 122.5 (q, JCF ¼ 32.0 Hz), 120.8, 119.2, 119.1 (q,
2.89. Found: C, 55.79; H, 2.63.
2
3JCF ¼ 4.0 Hz), 115.0, 114.7, 55.7 ppm.
2.3.17. N-(4-Chlorophenyl)-6-chlorobenzo[d]thiazol-2-amine, 3q
White solid, mp 206e207 ꢀC. 1H NMR (400 MHz, DMSO-d6):
2.3.10. N-(4-Fluorophenyl)-6-(trifluoromethyl)benzo[d]thiazol-2-
amine, 3j
d
¼ 10.68 (s, 1H), 7.91 (s, 1H), 7.81 (d, J ¼ 7.6 Hz, 2H), 7.58 (d,
J ¼ 8.0 Hz, 1H), 7.39 (d, J ¼ 7.6 Hz, 2H), 7.32 (d, J ¼ 8.0 Hz, 1H) ppm.
13C NMR (100 MHz, DMSO-d6):
White solid, mp 200e201 ꢀC. 1H NMR (400 MHz, DMSO-d6):
d
¼ 10.83 (s, 1H), 8.28 (s, 1H), 7.90e7.86 (m, 2H), 7.75 (d, J ¼ 8.4 Hz,
d
¼ 162.4, 151.3, 139.7, 132.2, 129.3,
1H), 7.63 (d, J ¼ 8.0 Hz, 1H), 7.26 (t, J ¼ 8.8 Hz, 2H) ppm. 13C NMR
126.8, 126.6, 126.2, 121.2, 120.7, 119.8 ppm. Anal. Calcd. for
C13H8N2SCl2: C, 52.88; H, 2.73. Found: C, 52.67; H, 2.91.
(100 MHz, DMSO-d6):
d
¼ 164.9, 158.2 (d, 1JCF ¼ 238.0), 155.4, 137.1,
1
3
131.2, 125.1 (q, JCF ¼ 270.0 Hz), 123.2 (q, JCF ¼ 4.0 Hz), 122.9 (q,
2JCF ¼ 32.0 Hz), 120.4 (d, 3JCF ¼ 8.0 Hz), 119.5, 119.2 (q, 3JCF ¼ 4.0 Hz),
2.3.18. N-Phenyl-6-methylbenzo[d]thiazol-2-amine, 3r
2
116.0 (d, JCF ¼ 23.0) ppm. Anal. Calcd. for C14H8N2F4S: C, 53.84; H,
White solid, mp 171e172 ꢀC (lit [41]. mp 154e155 ꢀC). 1H NMR
2.58. Found: C, 53.58; H, 2.74.
(400 MHz, DMSO-d6):
d
¼ 10.45 (s, 1H), 7.85 (d, J ¼ 7.6 Hz, 2H), 7.63
(s, 1H), 7.55 (d, J ¼ 8.4 Hz, 1H), 7.41 (t, J ¼ 8.0 Hz, 2H), 7.19e7.16 (m,
2.3.11. N-(4-Chlorophenyl)-6-(trifluoromethyl)benzo[d]thiazol-2-
amine, 3k
1H), 7.06 (t, J ¼ 7.2 Hz, 1H), 2.40 (s, 3H) ppm. 13C NMR (100 MHz,
DMSO-d6):
120.8, 118.8, 117.6, 20.8 ppm.
d
¼ 160.8, 150.0, 140.7, 131.5, 130.0, 128.9, 126.9, 121.8,
White solid, mp 190e192 ꢀC (lit [13]. mp 191e192 ꢀC). 1H NMR
(400 MHz, DMSO-d6):
d
¼ 10.93 (s, 1H), 8.30 (s, 1H), 7.89 (d,
J ¼ 8.8 Hz, 2H), 7.77 (d, J ¼ 8.0 Hz, 1H), 7.64 (d, J ¼ 8.0 Hz, 1H), 7.45
2.3.19. N-(4-Methoxyphenyl)-6-methylbenzo[d]thiazol-2-amine, 3s
White solid, mp 168e169 ꢀC (lit [41]. mp 160 ꢀC). 1H NMR
(d, J ¼ 8.4 Hz, 2H) ppm. 13C NMR (100 MHz, DMSO-d6):
d
¼ 164.1,
154.8, 139.0, 130.7, 128.7, 126.1, 124.6 (q, 1JCF ¼ 270.0 Hz), 122.7 (q,
(400 MHz, DMSO-d6):
d
¼ 10.18 (s, 1H), 7.68 (d, J ¼ 8.4 Hz, 2H), 7.55

R. Xiao et al. / Journal of Organometallic Chemistry 705 (2012) 44e50
47
(s, 1H), 7.44 (d, J ¼ 8.0 Hz, 1H), 7.11 (d, J ¼ 8.0 Hz, 1H), 6.95 (d,
J ¼ 8.4 Hz, 2H), 3.75 (s, 3H), 2.35 (s, 3H) ppm. 13C NMR (100 MHz,
higher order peaks (110) and (200) with lower intensities were also
detected, and therefore the chemical bonding procedure did not
diminish the structural ordering of the MCM-41. In order to confirm
that MCM-41-2N-CuSO4 is a neutral complex with the SO24ꢁ moiety
on the metal, the sulfur content of MCM-41-2N-CuSO4 was deter-
mined to be 0.45 mmol/g, which is close to the copper content of
0.43 mmol/g. In addition, we prepared the neutral analog [CuSO4/
H2NCH2CH2NH2 (1:1)] from the reaction of CuSO4 with ethyl-
enediamine in DMF. FT-IR spectrum of the analog [CuSO4/
H2NCH2CH2NH2 (1:1)] includes the characteristic absorptions of
SO24ꢁ at 1085 and 621 cmꢁ1, FT-IR spectrum of the MCM-41-2N-
CuSO4 also includes the characteristic absorptions of SO24ꢁ at 1069
and 622 cmꢁ1. These results indicated that a neutral copper
complex with the SO24ꢁ moiety on the metal is formed from the
reaction of MCM-41-2N with CuSO4.
DMSO-d6):
d
¼ 161.3, 154.6, 150.2, 134.2, 131.1, 130.0, 126.8, 120.8,
119.5, 118.5, 114.1, 55.1, 20.8 ppm.
2.3.20. N-(4-Chlorophenyl)-6-methylbenzo[d]thiazol-2-amine, 3t
Colorless oil [15]. 1H NMR (400 MHz, DMSO-d6):
d
¼ 10.60 (s,
1H), 7.88 (d, J ¼ 7.6 Hz, 2H), 7.65 (s, 1H), 7.56 (d, J ¼ 7.2 Hz, 1H), 7.45
(d, J ¼ 7.6 Hz, 2H), 7.19 (d, J ¼ 7.2 Hz, 1H), 2.41 (s, 3H) ppm. 13C NMR
(100 MHz, DMSO-d6):
127.5, 125.7, 121.4, 119.5, 119.4, 21.3 ppm.
d
¼ 161.0, 150.3, 140.1, 132.3, 130.5, 129.2,
2.3.21. N-(4-Nitrophenyl)-6-methylbenzo[d]thiazol-2-amine, 3u
Yellow solid, mp 272e273 ꢀC (lit [14]. mp 271e273 ꢀC). 1H NMR
(400 MHz, DMSO-d6):
d
¼ 11.09 (s, 1H), 8.23 (d, J ¼ 9.0 Hz, 2H), 7.97
(d, J ¼ 9.0 Hz, 2H), 7.65 (s, 1H), 7.58 (d, J ¼ 8.4 Hz, 1H), 7.18 (d,
J ¼ 8.0 Hz, 1H), 2.36 (s, 3H) ppm. 13C NMR (100 MHz, DMSO-d6):
3.2. Heterogeneous tandem reactions of 2-haloanilines with
isothiocyanates
d
¼ 159.7, 149.3, 146.4, 140.9, 132.7, 130.4, 127.3, 125.2, 121.0, 119.6,
117.0, 20.8 ppm.
In order to test the catalytic activity of the MCM-41-2N-CuSO4,
the tandem reactions of 2-haloanilines with isothiocyanates were
investigated under an air atmosphere. The reaction of 2-iodoaniline
with phenyl isothiocyanate (1.2 equiv) was chosen as a model
reaction, and the influences of various reaction parameters such as
solvent, base, and copper catalyst quantity on the reaction were
tested. The results are summarized in Table 1. For the solvents
evaluated such as EtOH, DMSO, DMF, dioxane, NMP, H2O, toluene
and DCE, DMSO was found to be the most effective. Our next
studies focused on the effect of base on the model reaction. Among
the bases examined, Et3N was found to be the most effective
(Table 1, entry 1), DBU and pyridine also afforded good yields
(Table 1, entries 9e11,19). While other bases such as K2CO3, Na2CO3,
K3PO4 and Cs2CO3 were ineffective (Table 1, entries 13e16), Et2NH,
piperidine and NaOAc were substantially less effective (Table 1,
entries 12, 17, 18). The amount of supported copper catalyst was
also screened, and 0.25 mol% loading of copper was found to be
optimal, a lower yield was observed when the amount of the
catalyst was decreased (Table 1, entry 20). Increasing the amount of
copper catalyst could shorten the reaction time, but did not
increase the yield of N-phenylbenzo[d]thiazol-2-amine (Table 1,
entry 21). Thus, the optimized reaction conditions for this tandem
reaction are MCM-41-2N-CuSO4 (0.25 mol%) in DMSO using Et3N as
base at 80 ꢀC under air for 8 h (Table 1, entry 1).
2.3.22. N-Cyclohexyl-6-methylbenzo[d]thiazol-2-amine, 3v
White solid, mp 173e174 ꢀC (lit [42]. mp 173e175 ꢀC). 1H NMR
(400 MHz, DMSO-d6):
d
¼ 7.82 (d, J ¼ 6.8 Hz, 1H), 7.42 (s, 1H), 7.25
(d, J ¼ 7.6 Hz, 1H), 7.00 (d, J ¼ 7.6 Hz, 1H), 3.72e3.63 (m, 1H), 2.30 (s,
3H), 2.00e1.96 (m, 2H), 1.74e1.70 (m, 2H), 1.60e1.55 (m, 1H),
1.38e1.14 (m, 5H) ppm. 13C NMR (100 MHz, DMSO-d6):
d
¼ 165.0,
151.1, 130.7, 130.2, 126.9, 121.2, 117.9, 53.2, 32.8, 25.8, 24.9, 21.2 ppm.
3. Results and discussion
3.1. Synthesis and characterization of MCM-41-2N-CuSO4
A novel 3-(2-aminoethylamino)propyl-functionalized MCM-41-
supported copper complex catalyst (MCM-41-2N-CuSO4) was very
conveniently synthesized starting from commercially available and
cheap 3-(2-aminoethylamino)propyltrimethoxysilane and CuSO4
according to Scheme 1. Firstly, the MCM-41 support reacted with 3-
(2-aminoethylamino)propyltrimethoxysilane in toluene at 100 ꢀC
for 24 h, followed by the silylation with Me3SiCl in toluene at room
temperature for 24 h to generate 3-(2-aminoethylamino)propyl-
functionalized MCM-41 (MCM-41-2N). Then the MCM-41-2N
reacted with CuSO4 in DMF at room temperature for 7 h to
generate the 3-(2-aminoethylamino)propyl-functionalized MCM-
41-immobilized copper complex catalyst (MCM-41-2N-CuSO4) as
a pale blue powder, the copper content of the catalyst was found to
be 0.43 mmol/g according to the ICP-AES measurements. The X-ray
powder diffraction (XRD) analysis of the new MCM-41-
immobilized copper complex catalyst (MCM-41-2N-CuSO4) indi-
cated that, in addition to an intense diffraction peak (100), two
With this promising result in hand, we started to investigate the
scope of both 2-halobenzenamines and isothiocyanates under the
optimized conditions, and the results are summarized in Table 2. As
showed in Table 2, a variety of isothiocyanates 2 were investigated
by reacting with 2-iodoaniline in the presence of 0.25 mol%
MCM-41-2N-CuSO4 and Et3N (2.0 equiv) at 80 ꢀC under aerobic
OSiMe
OH
3
1. (MeO)3Si(CH2)3NH(CH2)2NH2
O
OH
Toluene, 100 oC, 24 h
Si
N
H
NH2
O
OH
2. Me3SiCl, rt, 24 h
OMe
MCM-41-2N
MCM-41
OSiMe3
O
H
N
CuSO4, DMF
r.t., 7 h
Si
NH2
CuSO4
O
OMe
MCM-41-2N-CuSO4
Scheme 1. Preparation of MCM-41-2N-CuSO4.

48
R. Xiao et al. / Journal of Organometallic Chemistry 705 (2012) 44e50
Table 1
Reaction condition screening for the reaction of 2-iodoaniline with phenyl isothiocyanate.a
NH2
NCS
N
S
MCM-41-2N-CuSO4 (0.25 mol%)
base, solvent, 80 oC, air
+
NHPh
I
Entry
Solvent
Base
Time (h)
Yieldb (%)
1
2
3
4
5
6
7
8
DMSO
DMF
EtOH
Toluene
Dioxane
DCE
NMP
H2O
DMF
DMSO
Toluene
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
Et3N
Et3N
Et3N
Et3N
Et3N
Et3N
Et3N
Et3N
8
10
24
12
24
24
10
24
24
24
24
24
24
24
24
24
24
24
24
16
5
95
80
76
83
58
67
72
10
65
89
70
58
Trace
Trace
Trace
Trace
44
9
DBU
DBU
DBU
10
11
12
13
14
15
16
17
18
19
20c
21d
Et2NH
K2CO3
Na2CO3
K3PO4
Cs2CO3
Piperidine
NaOAc
Pyridine
Et3N
39
67
85
94
Et3N
a
Reaction conditions: 2-iodoaniline (1.0 mmol), phenyl isothiocyanate (1.2 mmol), MCM-41-2N-CuSO4 (0.25 mol%), base (2.0 mmol) in solvent (2.0 mL) at 80 ꢀC under an
air atmosphere.
b
c
Isolated yield.
0.13 mol% of copper catalyst was used.
0.5 mol% of copper catalyst was used.
d
Table 2
Heterogeneous tandem reaction of 2-halobenzenamines with isothiocyanates.a
NH2
N
S
MCM-41-2N-CuSO4(0.25 mol%)
DMSO, Et3N, 80 oC, air
R
NCS
NHR
+
R1
X
R1
1
2
3
Entry
R1/X
R
Time (h)
Product
Yieldb (%)
1
2
3
4
5
6
7
8
H/I
H/I
H/I
H/I
H/I
H/I
H/I
CF3/I
CF3/I
CF3/I
CF3/I
CF3/I
Cl/I
Cl/I
Cl/I
Cl/I
Cl/I
C6H5
8
8
10
8
8
5
3a
3b
3c
3d
3e
3f
3g
3h
3i
95
94
92
90
89
80
85
94
91
92
90
78
92
88
91
90
89
96
90
91
85
83
81
4-CH3C6H4
4-CH3OC6H4
4-FC6H4
4-ClC6H4
4-NO2C6H4
Cyclohexyl
C6H5
4-CH3OC6H4
4-FC6H4
4-ClC6H4
4-NO2C6H4
C6H5
4-CH3C6H4
4-CH3OC6H4
4-FC6H4
4-ClC6H4
C6H5
4-CH3OC6H4
4-ClC6H4
4-NO2C6H4
Cyclohexyl
C6H5
8
10
10
10
14
10
8
8
11
8
8
8
8
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
3j
3k
3l
3m
3n
3o
3p
3q
3r
3s
3t
CH3/I
CH3/I
CH3/I
CH3/I
CH3/I
H/Br
6
8
24
3u
3v
3a
a
Reaction conditions: 1 (1.0 mmol), 2 (1.2 mmol), MCM-41-2N-CuSO4 (0.25 mol%), Et3N (2.0 mmol) in DMSO (2.0 mL) at 80 ꢀC under an air atmosphere.
Isolated yield.
b

R. Xiao et al. / Journal of Organometallic Chemistry 705 (2012) 44e50
49
Table 3
Tandem reaction of 2-iodoaniline with phenyl isothiocyanate catalyzed by recycled catalyst.a
NH2
NCS
N
S
MCM-41-2N-CuSO4 (0.25 mol%)
Et3N, DMSO, 80 oC, 8 h, air
+
NHPh
I
Cycle
Yieldb (%)
Cycle
Yieldb (%)
1
3
5
7
9
95
94
94
93
92
2
4
6
8
10
95
93
94
93
93
a
Reaction conditions: 4-iodoaniline (10 mmol), phenyl isothiocyanate (12 mmol), MCM-41-2N-CuSO4 (0.025 mmol), Et3N (20 mmol) in DMSO (20 mL) at 80 ꢀC for 8 h
under an air atmosphere.
b
Isolated yield.
conditions. The results demonstrated that several functional
groups, such as methyl, methoxy, fluoro, chloro and nitro groups,
on the aryl moiety were tolerated well, and both electron-rich
and electron-poor aryl isothiocyanates underwent the tandem
reaction successfully in good to excellent yields (entries 2e6). 4-
Methoxyphenyl isothiocyanate, for example, was treated with 2-
iodoaniline to give the target product 3c in 92% yield (entry 3),
and the reaction of 4-nitrophenyl isothiocyanate with 2-iodoaniline
afforded the corresponding product 3f in 80% yield (entry 6). To our
delight, alkyl isothiocyanates were also suitable substrates for the
tandem reactions. Cyclohexyl isothiocyanate, for instance, was
treated with 2-iodoaniline under the same conditions to afford the
desired product 3g in 85% yield (entry 7). This heterogeneous
copper catalyst exhibited higher catalytic activity than CuSO4. For
example, the tandem reaction of 2-iodoaniline with phenyl iso-
thiocyanate in the presence of 0.25 mol% of MCM-41-2N-CuSO4 in
DMSO using Et3N as base at 80 ꢀC under air for 8 h gave a 95% yield
of N-phenylbenzo[d]thiazol-2-amine 3a (entry 1), the same reac-
tion in the presence of 1 mol% CuSO4 in DMSO using Et3N as base at
80 ꢀC under air for 10 h gave 3a in 91% yield.
Substituted 2-iodoanilines were subsequently investigated to
react with a variety of isothiocyanates under the optimized
conditions, and the results are also summarized in Table 2. We were
pleased to find that the optimized conditions were compatible with
various 2-iodoanilines bearing chloro, methyl and trifluoromethyl
groups. 4-Chloro-2-iodoaniline, for instance, underwent the
tandem reaction with phenyl isothiocyanate or substituted phenyl
isothiocyanates, smoothly in high yields (entries 13e17). 2-Iodo-4-
methylaniline was a suitable substrate under the same conditions
(entries 18e22). It was observed that the tandem reactions of
electron-withdrawing 2-iodo-4-(trifluoromethyl)aniline with
various isothiocyanates were also successful to afford the desired
products 3hel in good to excellent yields (entries 8e12). Interest-
ingly, a less active substrate, 2-bromoaniline, also displayed high
activity for the tandem reaction with phenyl isothiocyanate in 81%
yield (entry 23).
solution by ICP-AES. This result points to a process of heteroge-
neous nature.
3.3. Recycling of the catalyst
For a heterogeneous transition-metal catalyst, it is very important
to examine its ease of separation, good of recoverability and reus-
ability. We also investigated the recyclability of the MCM-41-2N-
CuSO4 by using the reaction of 2-iodoaniline with phenyl iso-
thiocyanate. This heterogeneous copper catalyst can be easily recov-
ered by simple filtration and washed with ethyl acetate and diethyl
ether. After being air-dried, it can be reused directly without further
purification. The recovered copper catalyst was used in the next run,
andalmostconsistent activitywasobserved for ten consecutivecycles
(Table 3). In addition, copper leaching in the supported catalyst was
also determined. The copper content of the catalyst was found by ICP
analysis to be 0.42 mmol/g after ten consecutive runs, only 2% of
copperhadbeen lostfrom theMCM-41 support. Thehighstabilityand
excellent reusability of the catalyst should result from the chelating
action of bidentate 2-aminoethylamino ligand on copper and the
mesoporousstructure of the MCM-41 support. The resultisimportant
from a practical point of view. The high catalytic activity, excellent
reusability and the easy accessibility of the MCM-41-2N-CuSO4 make
them ahighlyattractiveheterogeneous coppercatalystfortheparallel
solution phase synthesis of diverse libraries of compounds.
4. Conclusion
In summary, we have developed a novel, practical and envi-
ronmentally friendly catalyst system for the tandem reactions of 2-
haloanilines with isothiocyanates by using 0.25 mol% 3-(2-
aminoethylamino)propyl-functionalized
MCM-41-immobilized
copper complex as catalyst under an air atmosphere. The reac-
tions generated the corresponding 2-aminobenzothiazoles in good
to excellent yields. This novel heterogeneous copper catalyst can be
conveniently prepared by a simple two-step procedure from
commercially available and cheap reagents and exhibits higher
activity than CuSO4 and can be reused at least 10 times without any
decreases in activity. The tandem reactions of 2-haloanilines with
isothiocyanates catalyzed by the MCM-41-2N-CuSO4 complex
provide a better and practical procedure for the synthesis of
a variety of 2-aminobenzothiazoles.
A further objective of our studies was to determine whether the
catalysis was due to the MCM-41-2N-CuSO4 complex or to
a homogeneous copper complex that comes off the support during
the reaction and then returns to the support at the end. To test this,
we performed the hot filtration test [43]. We focused on the
tandem reaction of 2-iodoaniline with phenyl isothiocyanate. We
filtered off the MCM-41-2N-CuSO4 complex after 2 h of reaction
time and allowed the filtrate to react further. The catalyst filtration
was performed at the reaction temperature (80 ꢀC) in order to avoid
possible recoordination or precipitation of soluble copper upon
cooling. We found that, after this hot filtration, no further reaction
was observed and no copper could be detected in the filtered
Acknowledgments
We thank the National Natural Science Foundation of China
(Project No. 20862008) and the Natural Science Foundation of
Jiangxi Province (Project No. 2008GQH0034).

50
R. Xiao et al. / Journal of Organometallic Chemistry 705 (2012) 44e50
[21] A. Molnar, Chem. Rev. 111 (2011) 2251e2320.
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