Multicomponent, solvent-free synthesis of 1-Amidoalkyl-2-naphthols in the presence of H3+xPMo12-xVxO40 heteropolyacids as recyclable and green catalysts

Article abstract of DOI:10.1155/2011/954616

A rapid and efficient one-pot method for the synthesis of 1-amidoalkyl-2-naphthols has been developed in the presence of mixedaddenda vanadium(V)-substituted polyoxomolybdates including: H3+xPMo12- xVxO40 (x=1-3) heteropolyacids (HPAs) as recyclable catal

Full text of DOI:10.1155/2011/954616

ISSN: 0973-4945; CODEN ECJHAO
E-Journal of Chemistry
2011, 8(2), 523-528
http://www.e-journals.net
Multicomponent, Solvent-Free Synthesis of
1-Amidoalkyl-2-naphthols in the
Presence of H3+xPMo12-xVxO40 Heteropolyacids
as Recyclable and Green Catalysts
FATEMEH F. BAMOHARRAM§* , MAJID M. HERAVI# ,
MINA ROSHANI§ and MOHAMMAD J. SANE CHARKHI§
§Department of Chemistry, School of Sciences
Islamic Azad University - Mashhad Branch, Mashhad, Iran
#Department of Chemistry, School of Sciences
Alzahra University, Vanak, Tehran, Iran
Member of Young Researchers Club
Islamic Azad University – Mashhad Branch, Mashhad, Iran
abamoharram@yahoo.com
Received 15 June 2010; Accepted 1 September 2010
Abstract: A rapid and efficient one-pot method for the synthesis of
1-amidoalkyl-2-naphthols has been developed in the presence of mixed-
addenda vanadium(V)-substituted polyoxomolybdates including:H3+xPMo12-xVxO40
(x=1-3) heteropolyacids (HPAs) as recyclable catalysts under solvent-free
conditions. In all cases heteropolyacid with x = 3 gave the highest yield under
solvent-free conditions.
Keywords: Multicomponent reaction, Catalyst, Vanadium(V)-substituted Polyoxomolybdates,
1- Amidoalkyl-2-naphthols.
Introduction
The multicomponent coupling reactions1 are emerging as a useful source for accessing small
drug-like molecules with several levels of structural diversity. Multicomponent reaction
(MCR) condensations involve three or more compounds reacting in a single event, but
consecutively to form new products, which contains the essential parts of all the starting
materials. These reactions are welcome too in terms of economic and practical
considerations. The search and discovery for new MCRs on one hand2 and the full
exploitation of already known multicomponent reactions on the other hand, is therefore of
considerable current interest. 1-amidoalkyl-2-naphthols and their derivatives have attracted

524
F. F. BAMOHARRAM et al.
considerable interest in recent years due to biologically important antibacterial, natural
products and potent drugs including a number of nucleoside antibiotics and HIV protease
inhibitors, such as ritonavir and lipinavir3,4.
The preparation of 1-amidoalkyl-2-naphthols can be carried out by multi-component
condensation of aryl aldehydes, 2-naphthol and acetamide in the presence of Lewis or Bronsted
acid catalysts such as montmorillonite K10 clay5, Ce(SO4)26, iodine7, p-TSA8, sulfamic acid9 and
cation-exchange resins10. However, some of these catalysts suffer from the drawback of green
chemistry such as prolonged reaction times, low yields, toxicity and recovery and reusability of
the catalyst. Therefore, introducing clean processes and utilizing eco-friendly and green catalysts
which can be simply recycled at the end of reactions, have been under permanent attention. The
demand for environmentally benign procedure with heterogeneous and reusable catalysts
promoted us to develop a safe alternate method for the synthesis of amidoalkyl naphthols.
Recently, we have investigated various catalytic performances of heteropolyacids in
different reactions11-18. In seeking to develop new synthetic methods for organic compounds by
using heteropolyacids, in the present work, the performance and applicability of three kinds of
vanadium(V)-substituted polyoxomolybdates such as H4[PMo11VO40], H5[PMo10V2O40] and
H6[PMo9V3O40] has been studied for synthesis of 1-amidoalkyl-2-naphthols in one-pot and
solvent-free conditions. The results were compared with H3[PMo12O40].
Experimental
Heteropolyacid catalysts were synthesized according to the literature19. All of the chemicals were
obtained from commercial sources. All yields were calculated from purified products. IR spectra
were obtained with a Brucker 500 scientific spectrometer. 1H-NMR spectra were recorded on a FT
NMR 500 HZ spectrometer. Melting points were obtained on a Electro thermal type 9100 apparatus.
General procedure
In a typical reaction, a mixture of aromatic aldehyde (1.2 mmol) and 2-naphthol (1.2 mmol)
and acetamide (1.7 mmol) was made with a catalytic amount of mixed-addenda
o
vanadomolybdophosphate, (2 mol%), under solvent free conditions in oil bath at 130 C for
12 minutes. The progress of reaction was monitored by TLC. After completion of the
reaction, the mixture was cooled to 25 oC, then the solid residue was solved in boiling EtOH
and the mixture stirred for 8 minutes. The pure product was obtained by recrystallization.
Some selected spectroscopic data from (Table 2)
N-[Phenyl-(2-hydroxy-napthalen-1-yl)-methyl]-acetamide (Table 2, entry 2);1H NMR (500
MHz, DMSO-d6): δ=1.98 (s, 3H), 7.11 (m, 1H), 7.14(m, 1H), 7.16 (m, 1H), 7.19 (m, 1H),
7.20 (m, 2H), 7.21 (m, 1H), 7.23 (m, 1H), 7.33 (t, J=7.5 Hz, 1H), 7.73 (d, J=9.1 Hz, 1H),
7.78 (d, J=8.0 Hz, 1H), 7.83 (s, 1H), 8.45 (d, J=8.5 Hz, 1H),10.01 (s, 1H) ppm; 13C NMR
(125 MHz, DMSO-d6): 23.2, 40.3, 119.2, 119.4, 122.9, 123.8, 126.6, 126.8, 128.5, 126.8,
-1
128.9, 129.1, 129.8, 132.8, 143.1, 153.7, 169.0 ppm; IR (KBr, cm ): 3399, 3246, 3062,
1640, 1582, 1514, 1372, 1337, 1060, 808, 742, 696, 623.
N-[(3-Nitro-phenyl)-(2-hydroxy-napthalen-1-yl)-methyl]-acetamide (Table 2, entry 3)
1H NMR (500 MHz, DMSO-d6): δ=2.01 (s, 3H), 7.17 (t, J=8.0 Hz, 1H), 7.19 (d,J=8.6 Hz,
1H), 7.24 (t, J=7.5 Hz, 1H), 7.38 (t, J=7.4 Hz,1H), 7.51 (m, 2H), 7.78 (t, J=8.6 Hz, 2H), 7.83
(br, 1H), 7.98 (m, 2H), 8.58 (d, J=8.0 Hz, 1H), 10.16 (s, 1H) ppm; 13C NMR (125 MHz,
DMSO-d6): 23.1, 48.2, 118.3, 118.9, 120.9, 121.8, 123.2, 127.3, 123.2, 128.9, 129.2, 130.1,
-1
130.5, 132.6, 133.4, 145.9, 148.2, 153.9, 170.3 ppm; IR (KBr, cm ): 3373, 3088, 2598,
1645, 1524, 1350, 1232, 1158, 1063, 808, 705.

Multicomponent, Solvent-Free Synthesis
525
N-[(4-Nitro-phenyl)-(2-hydroxy-napthalen-1-yl)-methyl]-acetamide (Table 2, entry 4)
1H NMR (500 MHz, DMSO-d6): δ=2.02 (s, 3H), 7.19 (d, J=8.0 Hz, 1H), 7.22 (d, J=8.8 Hz,
1H), 7.28 (t, J=7.5 Hz, 1H), 7.41 (t, J=7.3 Hz, 1H), 7.52-7.58 (m, 2H), 7.81 (t, J=9.4 Hz,
2H), 7.87 (d, J=7.0 Hz, 1H), 8.03 (m, 2H), 8.60 (d, J=8.0 Hz, 1H), 10.11 (s, 1H) ppm; 13C
NMR (125 MHz, DMSO-d6): 22.5, 47.6, 117.7, 118.4, 120.3, 121.1, 122.5, 126.6, 128.3,
-1
129.4, 129.8, 132.1, 132.7, 145.3, 147.7, 153.2, 169.5 ppm; IR (KBr, cm ): 3391, 3267,
2593, 1648, 1603, 1522, 1438, 1063, 825, 739, 447.
N-[(4-Chloro-phenyl)-(2-hydroxy-napthalen-1-yl)-methyl]-acetamide (Table 2, entry 6)
1H NMR (500 MHz, DMSO-d6): δ=1.96 (s, 3H), 7.05 (d, J=8.1 Hz,1H), 7.11 (d, J=8.6 Hz,
2H), 7.18 (d, J=8.6 Hz, 1H), 7.19 (m, 3H), 7.31 (t, J=7.5 Hz, 1H), 7.73 (m, 3H), 8.42 (d,
J=8.6 Hz, 1H), 10.09 (s, 1H) ppm; 13C NMR (125 MHz, DMSO-d6): 20.6, 23.1, 48.1, 118.9,
119.0, 123.0, 126.9, 128.9, 128.4, 129.1, 129.1, 130.0, 131.2, 132.7, 142.3, 153.7, 169.9
-1
ppm; IR (KBr, cm ): 3392, 2962, 2700, 2613, 1637, 1577, 2523, 1490, 1436, 1374, 1331,
1278, 1243, 1171, 1091, 819, 747, 588, 499.
N-[(4-Methyl-phenyl)-(2-hydroxy-napthalen-1-yl)-methyl]-acetamide (Table 2, entry 7)
1H NMR (500 MHz, DMSO-d6): δ=1.96 (s, 3H), 2.21 (s, 3H), 7.03-7.08 (m, 5H), 7.19
(d, J=8.8 Hz, 1H), 7.24 (t, J=7.1 Hz, 1H), 7.34 (m, 1H), 7.74 (d, J=8.8 Hz, 1H), 7.78 (d,
J=7.9 Hz, 1H), 7.82 (br, 1H), 8.36 (d, J=8.1 Hz, 1H), 9.91 (s, 1H) ppm; 13C NMR (125
MHz, DMSO-d6): 20.4, 22.6, 47.6, 118.4, 118.9, 122.2, 123.1, 125.9, 126.1, 128.3,
-1
128.4, 128.9, 132.2, 134.9, 139.4, 143.2, 152.9,168.9 ppm; IR (KBr, cm ): 3396, 3055,
2923, 1625, 1515, 1437, 1276, 1181, 813, 744, 482.
Results and Discussion
The synthesis of 1-amidoalkyl-2-naphthols in the presence of a catalytic amount of various
heteropolyacids such as H6[PMo9V3O40], H5[PMo10V2O40], H4[PMo11VO40], was investigated
under solvent-free conditions (scheme 1).
O
H
HPAs
CH3CONH2
+
+
OH
O
Solvent-free
X
OH
NH
X
H3C
Scheme 1
To study the effect of the catalyst on this reaction, N-[(4-methoxy phenyl)-(2-hydroxy-
naphthalen-1-yl)-methyl]-acetamide, was selected as optimized and model product and the
yields of the products were obtained using different heteropolyacids as catalysts. The results
are shown in Table1. The suggested mechanism is shown in scheme 2.
Table 1. Effect of various heteropolyacids, (2 mol%), on the yields of N-[(4-
methoxyphenyl)-(2-hydroxy naphthalen-1-yl)-methyl]-acetamide under solvent-free conditions
at 130 oC
Entry
Heteropolyacid
H6[PMo9V3O40]
H5[PMo10V2O40]
H4[PMo11VO40]
H3[PMo12O40]
Time, min
Yield, %a
1
2
3
4
12
12
12
12
92
87
83
78
a Yield refers to isolated products

526
F. F. BAMOHARRAM et al.
Various HPAs
CH3CONH2
HPAs
OH
O
+
ArCHO
O
Solvent-free
OH
NH
X
Ar
H
H3C
O-QMs
Scheme 2
The reaction of 2-naphthol with aromatic aldehydes in the presence of acid catalyst is
known to give ortho-quinone methides (O-QMs). The same O-QMs, generated in situ, have
been reacted with acetamide to form 1-amidoalkyl-2-naphthol derivatives. A reasonable
explanation for this result can be given by considering the nucleophilic addition to O-QM
intermediate favourable via conjugate addition on α,β-unsaturated carbonyl group that
aromatizes ring of this intermediate. The order of efficiency of catalysts is as follows:
H6[PMo9 V3O40] > H5[PMo10V2O40] > H4[PMo11VO40] > H3[PMo12O40]. Thus, H6[PMo9V3O40]
was selected as the catalyst of choice for the synthesis of 1-amidoalkyl-2-naphthols. The
results are shown in Table 2.
Table 2. Synthesis of 1-amidoalkyl-2-naphthols using catalytic amount of H6[PMo9V3O40]
(2 mol% ) under solvent-free conditions at 130 oC
mp., oC
Entry
Aldehyde
Time, min Yield, %a
Found
186-187
241
Reported[Ref.]
184-186[6]
241-243[6]
182-184[6]
148-149[26]
228-230[9]
248-250[6]
222-223[24]
1
2
3
4
5
6
7
4-CH3OC6H4CHO
C6H5CHO
12
12
12
12
12
12
12
92
84
87
89
90
89
84
3-NO2C6H4CHO
4- NO2C6H4CHO
4-BrC6H4CHO
4-ClC6H4CHO
4-CH3C6H4CHO
188-189
151
226
243-244
225-226
a Yield refers to isolated products
The Keggin anion with x=0, have an assembly of 12 corner-shared octahedral MoO6
from trimetallic groups [Mo3O13] around a heteroatom tetrahedron PO420. The
introduction of vanadium (V) into the Keggin framework of [PMo12O40]3- is beneficial
for catalysis reactions21. Usually positional isomers are possible and coexist when two
or more vanadium atoms are incorporated into the mixed-addenda Keggin structure22.
Studies on these isomers in catalytic reactions indicate that different isomers cause to
show different reactivities23. With respect to the catalytic performances for these
catalysts and the overall effects of all isomers, for synthesizing of them, we cannot
control the reaction conditions to synthesis of positional vanadium-substituted isomers
separately and hence study of their catalytic activity, is difficult. It is suggested that the
presence of both Bronsted acidity and vanadium in the structure of mentioned
heteropolyacids, is responsible for catalytic activity of mixed-addenda Keggins. The
greater protons number may lower, the activation energy barrier and the greater
vanadium atoms may provide many sites for catalytic reaction.
To optimize the temperature in the mentioned reaction, N-[(4-Methoxy phenyl)-(2-
hydroxy-naphthalen-1-yl)-methyl]-acetamide, was selected and the temperature effect was
carefully investigated. The reaction was carried out in the presence of best catalyst:
H6[PMo9V3O40] heteropolyacid, under solvent-free conditions. The temperature varied from

Multicomponent, Solvent-Free Synthesis
527
o
room temperature to130 C. The results showed that the highest yield can be obtained at
130 oC. The yields was lower when the reactions were carried out at temperatures lower than
reflux temperature. We believe that increasing in the temperature for accelerating the
reaction is apparently favorable.
Under optimum conditions, different amount of catalyst including 1%, 2% and 3 mol%
have been studied. The results are shown in Figure 1. It is clear that the yields depend on the
amount of catalyst and the optimum amount of which was 2 mol% for all derivatives.
Increase in this amount has not any effect on the yield.
92
100
80
60
40
20
0
88
48
1
2
Catalyst amount, mol%
3
Figure 1. The result of using different amounts of H6[PMo9V3O40] in the synthesis of
N-[(4-methoxyphenyl)-(2-hydroxy-naphthalen-1-yl)-methyl]-acetamide under solvent-free
conditions
Reusability of the catalyst
The catalyst was recovered after the reaction and reused in the reaction. Several times
recoveries had only slightly decreased the catalytic activity, pointing to the stability and
retention capability of this useful polyanion. At the end of the reaction, the catalyst was
filtered, washed with diethyl ether, dried and reused in another reaction. The recycled catalyst
was used for three reactions without observation of appreciable lost in its catalytic activities.
Conclusion
In conclusion, we have reported a new catalytic method for the synthesis of 1-amidoalkyl-2-
naphthols derivatives by using vanadium(V)-substituted polyoxomolybdates as efficient,
inexpensive, reusable and eco-friendly heterogeneous catalysts, via three-component
reactions, under solvent-free conditions. The solvent-free green procedure offer advantages
such as shorter reaction times, simple work up and excellent yield. Simple experimental
procedure as well as high yield and selectivity, makes this method useful addition to the
methodologies that require green super acid solid catalyst. Important features of this
protocol are, simplicity and versatility of process engineering, decreasing reactor and plant
corrosion problems and environmentally safe disposal. The catalyst can be easily recovered,
regenerated and reused without loss of structure and appreciable activity, thus providing
economic and environmentally friendly method for other organic reactions.
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