Solvent-free synthesis of 1-(benzothiazolylamino)methyl-2-naphthols with maltose as green catalyst

Article abstract of DOI:10.1007/s11164-014-1843-y

We report an efficient and entirely green procedure for preparation of 1-(benzothiazolylamino)methyl-2-naphthol derivatives involving multi-component, one-pot condensation reaction of 2-naphthol, 2-aminobenzothiazole, and aromatic aldehydes in the presenc

Full text of DOI:10.1007/s11164-014-1843-y

Res Chem Intermed
DOI 10.1007/s11164-014-1843-y
Solvent-free synthesis of 1-(benzothiazolylamino)
methyl-2-naphthols with maltose as green catalyst
•
Belgheis Adrom Malek Taher Maghsoodlou
•
•
Nourallah Hazeri Mojtaba Lashkari
Received: 18 July 2014 / Accepted: 5 October 2014
Ó Springer Science+Business Media Dordrecht 2014
Abstract We report an efficient and entirely green procedure for preparation of
1-(benzothiazolylamino)methyl-2-naphthol derivatives involving multi-component, one-
pot condensation reaction of 2-naphthol, 2-aminobenzothiazole, and aromatic aldehydes
in the presence of maltose under solvent-free conditions. This method has several
advantages, including mild conditions, high yields, clean reaction profile, simple oper-
ation, and environmentally benign and simple work-up procedures.
Keywords Green procedure Á 1-(Benzothiazolylamino)methyl-2-naphthol Á
Multi-component reaction Á Maltose Á Solvent-free conditions
Introduction
Multi-component reactions (MCR) are important in combinatorial chemistry
because of their suitability for synthesis of small drug-like molecules with
structural diversity. These reactions enable compound synthesis in few steps,
usually in one pot [1]. Among the advantages of these reactions are that they are
inexpensive, simple, and time and energy-saving with high bond-forming
efficiency [2]. Therefore finding and designing new MCR has been the subject of
extensive research.
In modern organic synthesis, biologically active benzothiazoles are regarded as
valuable building blocks. 2-Aminobenzothiazoles are unique structures that are
widely used in medicinal and biological chemistry [3]. Their diverse functions range
from facilitation of electron transfer in the firefly luciferine cycle [4], and, in
pharmaceutical chemistry, antitumor [5] and antidiabetic activity [6], use as
B. Adrom Á M. T. Maghsoodlou (&) Á N. Hazeri Á M. Lashkari
Department of Chemistry, Faculty of Science, University of Sistan and Baluchestan,
P. O. Box 98135-674, Zahedan, Iran
e-mail: mt_maghsoodlou@chem.usb.ac.ir; mt_maghsoodlou@yahoo.com
123

B. Adrom et al.
indicators of Alzheimer’s disease [7], and anticancer activity [8]. Benzothiazoles are
also commercially important as reactive dyes [9], hair dyes [10] agrochemical
fungicides, insecticides, acaricides, herbicides, plant desiccants, and defoliants [11].
Because of the biological activity of 2-aminobenzothiazoles, and as part of our
ongoing program on MCR [12, 13], herein we report an eco-friendly, simple, and
efficient method for synthesis of 1-(benzothiazolylamino)methyl-2-naphthols by
one-pot three-component reaction of 2-naphthol, 2-aminobenzothiazole, and
aromatic aldehydes in the presence of maltose under solvent-free conditions
(Scheme 1).
The principles of green chemistry were introduced to eliminate or reduce the use
of hazardous materials such as H2SO4 or H3PO4 in chemical processes. Cleaner
techniques make use of such environmentally benign materials as carbohydrates,
which are also inexpensive and safe [14]. For this reason, we focused our
investigation on developing new, environmentally benign synthetic methods for
preparation of 1-(benzothiazolylamino)methyl-2-naphthols. This one-pot reaction
under solvent-free conditions is not only operationally simple, clean, and efficient
but also consistently gives the corresponding products in good to excellent yields.
Results and discussion
We performed a set of preliminary experiments with 2-naphthol, 2-aminobenzo-
thiazole, and benzaldehyde in the presence of different catalysts as model reaction.
Initially, different carbohydrates were screened as catalyst in the model reaction.
The reaction did not progress even after 24 h in the absence of catalyst. When the
reaction was performed in the presence of sucrose, xylose, or lactose the product
was obtained in moderate yields. However, 20 mol% maltose proved an efficient
catalyst giving high yields. As shown in Table 1, the shortest reaction time and best
yield were achieved at 80 °C. Increasing the amount of catalyst or the temperature
did not improve the results.
To evaluate the generality of the process, use of the method for synthesis of other
1-(benzothiazolylamino)methyl-2-naphthols (4) was studied (Table 2). Reaction of
2-naphthol with a variety of aromatic aldehydes and 2-aminobenzothiazole was
performed in the presence of 20 mol% maltose at 80 °C. In all the reactions, good to
excellent yields were obtained in short reaction times (5–15 min). Using these
optimized reaction conditions, use of several types of aldehyde was investigated. As
shown in Table 2, the direct three-component reactions worked well with a variety
of aryl aldehydes, including those bearing electron-withdrawing and electron-
donating groups, and the desired products were obtained in good yields, although
product yield was lower for aryl aldehydes containing electron-withdrawing
substituents.
A suggested mechanism for this transformation is proposed in Scheme 2. As
reported in the literature [15–19], reaction of 2-naphthol with aldehydes in the
presence of catalyst is known to give ortho-quinone methides (o-QMs). The same o-
QMs, generated in situ, have been reacted with 2-aminobenzothiazole via conjugate
123

Solvent-free synthesis
S
N
R
N
H
O
S
OH
Maltose (20 mol %)
solvent-free, 80 °C
OH
+
H2N
+
Ar
H
N
1
2
3
4a-t
Scheme 1 Maltose-catalyzed synthesis of 1-(benzothiazolylamino)methyl-2-naphthols 4a–t
Table 1 Optimization of the catalyst for synthesis of 1-(benzothiazolylamino)methyl-2-naphthola
Entry
Catalyst (mol%)
Temperature (°C)
Time (min)
Isolated Yield (%)
1
2
3
4
5
6
7
8
9
9
9
a
Lactose (10)
Sucrose (10)
Xylose (10)
Maltose (10)
Maltose (15)
Maltose (20)
Maltose (30)
Maltose (20)
Maltose (20)
Maltose (20)
Maltose (20)
80
80
80
80
80
80
80
60
25
50
100
20
14
30
14
10
10
8
45
60
25
80
85
93
87
35
–
20
90
90
8
10
55
Reaction conditions: 2-naphthol (1.0 mmol), 2-aminobenzothiazole (1.0 mmol), and benzaldehyde
(1.0 mmol) in the presence of different catalysts at different temperatures
addition to form 1-(benzothiazolylamino)methyl-2-naphthols 4a–t. There is an
alternative pathway, a Mannich-type reaction (Scheme 3).
1
The products were characterized by IR, H NMR, and 13C NMR spectroscopy.
1
The H NMR spectrum of 4s contained a multiplet at d = 7.15–7.45 for the seven
aromatic hydrogens and an aliphatic CH, and two singlets at d = 8.61 and d = 9.92
for the NH and OH groups, respectively.
Experimental
General
Melting points and IR spectra were measured on an Electrothermal 9100 apparatus
1
and a Jasco FT/IR- 460 plus spectrometer, respectively. H and 13C NMR spectra
were obtained on Bruker DRX-400 Avance instruments with DMSO as a solvent.
123

B. Adrom et al.
Table 2 Synthesis of 1-(benzothiazolylamino)methyl-2-naphthol derivatives
Entry
Ar
Time (min)
Yield (%)a
Product
M.p. (lit. m.p.) (°C) [Ref.]
1
4-O2N-C6H4
4-Cl-C6H4
15
5
45
89
50
82
89
90
88
89
92
58
86
95
92
82
90
90
93
89
90
92
4a
4b
4c
4d
4e
4f
188–190 (189–191) [15]
208–210 (209–210) [16]
190–192 (191-194) [17]
204–206 (206–207) [15]
185–187 (184–186) [17]
183–185 (182–183) [16]
187–189 (189–190) [15]
162–164 (161–163) [17]
173–175 (175–176) [16]
212–214 (215–216) [15]
194–196 (193–195) [20]
200–202 (202–204) [17]
200–202 (200–202) [20]
175–177 (176–178) [17]
181–183 (183–185) [20]
190–192 (191–193) [20]
200–202 (201–203) [20]
202–204 (202–203) [15]
209–211b
2
3
3- O2N-C6H4
2,4-Cl2C6H3
3-MeO-C6H4
4-Me-C6H4
6
4
6
5
7
6
12
6
7
2-Cl-C6H4
4g
4h
4i
8
2,4-(MeO)2-C6H3
4-MeO-C6H4
2- O2N-C6H4
2,6-Cl2-C6H3
3-Br-C6H4
10
9
9
10
11
12
13
14
15
16
17
18
19
20
a
15
8
4j
4k
4l
5
4-Br-C6H4
5
4m
4n
4o
4p
4q
4r
4s
4-F-C6H4
13
9
5-Br,2-HO-C6H3
C4H3S
10
12
10
12
8
2,3-(MeO)2-C6H3
Ph
2,5-(MeO)2-C6H3
5- MeO, 2-HO-C6H3
4t
200–202b
Isolated yield
b
New compounds synthesized in this work
All reagents and solvents were obtained from Fluka and Merck and used without
further purification.
Typical procedure for the synthesis of 1-amidoalkyl -2-naphthols (4a–t)
Maltose (20 mol%, 0.068 g) was added to a mixture of benzaldehyde (1.0 mmol),
2-naphthol (1.0 mmol), and 2-aminobenzothiazole (1.0 mmol), then the reaction
mixture was heated to 80 °C and maintained for the appropriate time (Table 1).
After completion of the reaction (monitored by TLC), the reaction mixture was
washed with H2O (3 9 10 mL). The catalyst is soluble in water and was removed
from the reaction mixture. The residue was then recrystallized from EtOH to furnish
the pure product. Analytical and spectral data for the products are listed below:
1-((benzo[d]thiazol-2-ylamino)(4-chlorophenyl)methyl)naphthalen-2-ol (4b) Yield:
89 %; m.p. 208–210 °C; 1H NMR (400 MHz, DMSO-d6): d = 6.81 (s, 1H,
H
aromatic), 6.89–6.91 (m, 1H, Haromatic), 7.00–7.04 (m, 1H, Haromatic), 7.19–7.30 (m,
3H, Haromatic), 7.33 (d, 1H, J = 5.2 Hz, Haromatic), 7.39 (d, 2H, J = 8 Hz, Haromatic),
7.46(s, 1H, Haromatic), 7.67 (d, 1H, J = 7.6 Hz, Haromatic), 7.80 (t, 2H, J = 7.6 Hz,
H
aromatic), 8.00 (d, 1H, J = 8 Hz, Haromatic),8.94 (s, 1H, NH), 10.27 (s, 1H, OH).
123

Solvent-free synthesis
Maltose
Ar
H
H
H
O
OH
O
O
+
Ar
1
2
o-QMs
S
N
Maltose
Ar
H
H
O
R
N
O
N
H
OH
NH2
+
S
o-QMs
3
4
Scheme 2 Suggested mechanism for synthesis of 1-(benzothiazolylamino)methyl-2-naphthols based on
o-QMs
Maltose
H
O
O
N
N
S
+
NH2
N
H
Ar
S
Ar
3
2
A
OH
N
Mannich-type
+
N
4
S
Ar
1
A
Scheme 3 Suggested mechanism for synthesis of 1-(benzothiazolylamino)methyl-2-naphthols based on
the Mannich-type reaction
1-((benzo[d]thiazol-2-ylamino)(2,4-dichlorophenyl)methyl)naphthalen-2-ol (4d) Yield:
84 %; m.p. 204–206 °C; 1H-NMR (400 MHz, DMSO-d6): d = 7.01 (t, J = 7.2 Hz,
1H), 7.13–7.21 (m, 3H), 7.27 (t, J = 7.6 Hz, 1H), 7.37–7.42 (m, 3H), 7.50 (s,1H),
123

B. Adrom et al.
7.67(t, J = 8 Hz, 2H), 7.77–7.82 (m, 2H), 8.02 (d, J = 8.4 Hz, 1H), 8.89 (s, NH),
9.98 (broads, 1H, OH).
1-((benzo[d]thiazol-2-ylamino)(3-methoxyphenyl)methyl)naphthalen-2-ol (4e) Yield:
89 %; m.p. 185–187 °C; IR (KBr, cm-1): 1H NMR (400 MHz, DMSO-d6):
d = 3.65 (s, 3H, OCH3), 6.76 (d, 1H, J = 7.6 Hz, Haromatic), 6.80 (d, 1H,
J = 7.6 Hz, Haromatic), 6.83 (s, 1H, Haromatic), 7.01 (t, 1H, J = 7.2 Hz, Haromatic),
7.16–7.38(m, 7H, Haromatic,1Hbenzylic), 7.67 (d, 1H, J = 7.6 Hz, Haromatic), 7.79 (t,
1H, J = 7.8 Hz, Haromatic), 7.88 (brs, 1H, Haromatic), 8.79 (s, 1H, NH), 10.17 (s, 1H,
OH).
1-((benzo[d]thiazol-2-ylamino)(2-chlorophenyl)methyl)naphthalen-2-ol (4g) Yield:
1
88 %; m.p. 187–189 °C; H NMR (400 MHz, DMSO-d6): d = 6.97–7.01 (m, 1H,
Haromatic), 7.15–7.36 (m, 9H, Haromatic), 7.64 (d, 2H, J = 6.8 Hz, Haromatic),
7.76–7.81 (m, 2H, Haromatic), 8.05(d, 1H, J = 7.6 Hz, Haromatic), 8.85 (s, 1H, NH),
9.96 (s, 1H, OH).
1-((benzo[d]thiazol-2-ylamino)(2,4-dimethoxyphenyl)methyl)naphthalen-2-ol (4h) Yield:
1
89 %; m.p. 162–164 °C; H NMR (400 MHz, DMSO-d6): d = 3.63 and 3.70(2s,
6H, 2OCH3), 6.44–7.75 (m, 13H), 8.19 (broads, 1H), 8.55 (s, 1H, NH), 9.92 (s, 1H,
OH).
1-((benzo[d]thiazol-2-ylamino)(4-methoxyphenyl)methyl)naphthalen-2-ol (4i)
1
Yield: 92 %; m.p. 173-175 °C; IR (KBr, cm-1): H NMR (400 MHz, DMSO-d6):
d = 3.68 (s, 3H, OCH3), 6.83 (d, 1H, J = 8.4 Hz, Haromatic), 7.00 (t, 1H,
J = 7.2 Hz, Haromatic), 7.15–7.36(m, 8H, Haromatic,1Hbenzylic), 7.78 (t, 2H,
J = 8.8 Hz, Haromatic), 7.88 (brs, 1H), 8.77 (s, 1H, NH), 10.14 (s, 1H, OH).
1-((benzo[d]thiazol-2-ylamino)(2-nitrophenyl)methyl)naphthalen-2-ol (4j) Yield:
58 %; m.p. 212–214 °C; 1H NMR (400 MHz, DMSO-d6): d = 7.06 (t, 2H,
J = 7.6 Hz, Haromatic), 7.22–7.26 (m, 2H, Haromatic), 7.39–7.47(m, 3H, Haromatic),
7.67–7.91 (m, 8H, Haromatic), 8.84 (s, 1H, NH), 9.89 (brs, 1H, OH).
1-((benzo[d]thiazol-2-ylamino)(2,6-dichlorophenyl)methyl)naphthalen-2-ol (4 k) Yield:
86 %; m.p. 194–196 °C; 1H-NMR (400 MHz, DMSO-d6): d = 6.99–7.07 (m,
2H, Haromatic), 7.17–7.38 (m, 7H, Haromatic, Hbenzylic), 7.45 (t, J = 7.2 Hz, 1H,
Haromatic), 7.65 (d, J = 7.6 Hz, 1H, Haromatic), 7.76 (d, J = 8.8 Hz, 1H, Haromatic),
7.82 (d, J = 8.0 Hz, 1H, Haromatic), 7.96 (d, J = 8.8 Hz, 1H, Haromatic), 8.78 (d,
J = 6.4 Hz, 1H, NH), 9.74 (s, 1H, OH).
1-((benzo[d]thiazol-2-ylamino)(3-bromophenyl)methyl)naphthalen-2-ol (4 l) Yield:
90 %; m.p. 200–202 °C; 1H NMR (400 MHz, DMSO-d6): d = 6.86 (s, 1H,
Haromatic), 7.00 (t, J = 7.2 Hz, 1H), 7.18–7.28 (m, 5H, Haromatic, Hbenzylic),
7.36–7.38 (m, 3H, Haromatic), 7.65 (d, J = 7.6 Hz, 1H), 7.75–7.80 (m, 2Haromatic),
7.99 (s, 1H, Haromatic), 8.89 (s, 1H, NH), 10.20 (brs, 1H, OH).
1-((benzo[d]thiazol-2-ylamino)(4-bromophenyl)methyl)naphthalen-2-ol (4m) Yield:
90 %; m.p. 200–202 °C; 1H NMR (400 MHz, DMSO-d6): d = 7.02 (t,
J = 7.6 Hz, 1H, Haromatic), 7.17–7.28 (m, 6H, Haromatic, Hbenzylic), 7.38 (d,
123

Solvent-free synthesis
J = 8 Hz, 2H, Haromatic), 7.46 (d, J = 8.4 Hz, 2H, Haromatic), 7.67 (d, J = 7.6 Hz,
1H, Haromatic), 7.79–7.82 (m, 2H, Haromatic), 8.81 (brs, 1H, NH), 10.22 (brs, 1H, OH).
1-((benzo[d]thiazol-2-ylamino)(5-bromo-2-hydroxyphenyl)methyl)naphthalen-2-ol (4o)
Yield: 90 %; m.p. 181–183 °C; 1H NMR (400 MHz, DMSO-d6): d = 6.69 (d,
J = 8.4 Hz, 1H, Haromatic), 6.98 (t, J = 7.6 Hz, 1H, Haromatic), 7.13–7.28 (m, 6H,
H
H
aromatic, Hbenzylic), 7.34 (d, J = 8 Hz, 1H, Haromatic), 7.43 (t, J = 7.2 Hz, 1H,
aromatic), 7.62–7.64 (m, 2H, Haromatic), 7.72 (d, J = 8.4 Hz, 1H, Haromatic), 7.77 (d,
J = 7.6 Hz, 1H, Haromatic), 8.25 (d, J = 8.4 Hz, 1H, Haromatic), 8.70 (s, 1H, NH),
9.62–10.28 (br, 2H, OH).
1-((benzo[d]thiazol-2-ylamino)(thiophen-2-yl)methyl)naphthalen-2-ol (4p) Yield:
90 %; m.p. 192–194 °C; 1H-NMR (400 MHz, DMSO-d6): d = 7.02 (t, J = 7.6 Hz,
1H, Haromatic), 7.19–7.39 (m, 10H, Haromatic, Hbenzylic), 7.68 (d, J = 7.6 Hz, 1H,
H
aromatic), 7.79–7.82 (m, 2H, Haromatic), 8.82 (s, 1H, NH), 10.21 (br, 1H, OH).
1-((benzo[d]thiazol-2-ylamino)(2,5-dimethoxyphenyl)methyl)naphthalen-2-ol (4s)
1
Yield: 90 %; m.p. 209–211 °C; IR (KBr, cm-1): 3,368 (N–H), 3,060, 1,628; H
NMR (400 MHz, DMSO-d6): d = 3.50 and 3.64 (2s, 2OCH3, 6H), 6.76 (d,
J = 8.4 Hz, 1H, Haromatic), 6.84 (d, J = 8.8 Hz, 1H, Haromatic), 6.98 (d, J = 7.2 Hz,
1H, Haromatic), 7.15–7.45 (m, Haromatic, 7H, 1Hbenzylic), 7.63 (d, J = 7.6 Hz, 1H,
H
aromatic), 7.71 (d, J = 8.8 Hz, 3H, Haromatic), 7.77 (d, J = 8 Hz, 1H, Haromatic), 8.26
(d, J = 8.4 Hz, 1H, Haromatic), 8.61 (brs, 1H, NH), 9.92 (s, 1H, OH); 13C NMR
(400 MHz, DMSO-d6): d = 50.56, 55.69, 56.44, 111.64, 112.41, 116.22, 118.46,
118.72, 119.06, 121.22, 121.26, 122.66, 123.89, 125.82, 126.39, 128.70, 128.80,
129.51, 131.07, 131.70, 133.06, 151.37, 152.74, 153.24, 153.81, 166.14.
1-((benzo[d]thiazol-2-ylamino)(2-hydroxy-3-methoxyphenyl)methyl)naphthalen-2-
ol (4t) Yield: (92 %); m.p. 200–202 °C; IR (KBr, cm-1): 3,366, 3,141, 1,632; 1H
NMR (400 MHz, DMSO-d6): d = 3.74 (S, 3H, OCH3), 6.67 (t, J = 7.6 Hz, 1H,
H
aromatic), 6.82 (d, J = 7.6 Hz, 1H, Haromatic), 6.96 (t, J = 7.6 Hz, 1H, Haromatic),
7.01 (d, J = 7.2 Hz, 1H, Haromatic), 7.14–7.40 (m, 6H, Haromatic, Hbenzylic), 7.61 (d,
J = 7.2 Hz, 1H, Haromatic), 7.71 (d, J = 8 Hz, 1H, Haromatic), 7.76 (d, J = 8 Hz, 1H,
H
aromatic), 8.18 (d, J = 8.4 Hz, 1H, Haromatic), 8.64 and 8.79 (2brs, 2H, NH and OH),
9.95 (brs, 1H, OH); 13C NMR (400 MHz, DMSO-d6): d = 50.90, 56.12, 56.27,
110.81, 118.29, 118.53, 118.86, 119.16, 121.13, 121.24, 122.66, 123.43, 125.81,
126.42, 128.82, 129.30, 130.96, 132.17, 133.22, 144.29, 147.79, 151.68, 152.69,
153.66, 166.27.
Conclusions
In conclusion, we have developed a new method for preparation of 1-(ben-
zothiazolylamino)methyl-2-naphthols by one-pot, three-component reaction of
2-naphthol with aromatic aldehydes and 2-aminobenzothiazole. Maltose is used
as neutral organic catalyst, at 80 °C, under solvent-free conditions. The catalyst is
environmentally benign, inexpensive, clean, safe, nontoxic, and readily available.
This method has several other advantages including mild reaction conditions, high
123

B. Adrom et al.
yields, and simplicity; it is also clean, and performed under neutral reaction
conditions. These advantages make it a useful and attractive process for synthesis of
a wide variety of biologically active compounds.
Acknowledgments We gratefully acknowledge financial support from the Research Council of the
University of Sistan and Baluchestan.
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