Nanocrystalline copper(II) oxide-catalyzed one-pot synthesis of imidazo[1,2-a]quinoline and quinolino[1,2-a]quinazoline derivatives via a three-component condensation

Article abstract of DOI:10.1080/00397910903576693

A simple, efficient, and practical procedure for the synthesis of imidazo[1,2-a]quinoline and quinolino[1,2-a]quinazoline derivatives using CuO nanoparticles as a novel catalyst in excellent yields is described. The catalyst can be recovered conveniently

Full text of DOI:10.1080/00397910903576693

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Nanocrystalline Copper(II)
Oxide–Catalyzed One-Pot Synthesis
of Imidazo[1,2-a]quinoline and
Quinolino[1,2-a]quinazoline Derivatives
via a Three-Component Condensation
Seyed Javad Ahmadi a , Morteza Hosseinpour b & Sodeh Sadjadi a
a Nuclear Fuel Cycle School, Nuclear Science and Technology
Research Institute, Tehran, Iran
b Department of Energy Engineering, Sharif University of Technology,
Tehran, Iran
Version of record first published: 13 Jan 2011.
To cite this article: Seyed Javad Ahmadi , Morteza Hosseinpour & Sodeh Sadjadi (2011):
Nanocrystalline Copper(II) Oxide–Catalyzed One-Pot Synthesis of Imidazo[1,2-a]quinoline
and Quinolino[1,2-a]quinazoline Derivatives via a Three-Component Condensation, Synthetic
Communications: An International Journal for Rapid Communication of Synthetic Organic Chemistry,
41:3, 426-435
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Synthetic Communications1, 41: 426–435, 2011
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397910903576693
NANOCRYSTALLINE COPPER(II) OXIDE–CATALYZED
ONE-POT SYNTHESIS OF IMIDAZO[1,2-a]QUINOLINE
AND QUINOLINO[1,2-a]QUINAZOLINE DERIVATIVES
VIA A THREE-COMPONENT CONDENSATION
Seyed Javad Ahmadi,1 Morteza Hosseinpour,2 and
Sodeh Sadjadi1
1Nuclear Fuel Cycle School, Nuclear Science and Technology Research
Institute, Tehran, Iran
2Department of Energy Engineering, Sharif University of Technology,
Tehran, Iran
A simple, efficient, and practical procedure for the synthesis of imidazo[1,2-a]quinoline and
quinolino[1,2-a]quinazoline derivatives using CuO nanoparticles as a novel catalyst in
excellent yields is described. The catalyst can be recovered conveniently and reused at least
four times without any loss of activity.
Keywords: CuO nanoparticles; imidazo[1,2-a]quinoline; quinolino[1,2-a]quinoline
INTRODUCTION
Heterocyclic chemistry has always been one of the most valuable sources of
novel compounds with diverse biological activity, mainly because of the unique
ability of the compounds to mimic the structure of peptides and to bind reversibly
to proteins. To medicinal chemists, the true utility of heterocyclic structures is the
ability to synthesize one library based on one core scaffold and screen it against a
variety of different receptors, yielding several active compounds.
Almost unlimited combinations of fused heterocyclic structures can be
designed, resulting in novel polycyclic frameworks with the most diverse physical,
chemical, and biological properties.
The fusion of several rings leads to geometrically well-defined rigid polycyclic
structures and thus holds the promise of a high functional specialization, resulting
from the ability to orient substituents in three-dimensional spaces. Therefore,
efficient methodologies resulting in polycyclic structures from biologically active het-
erocyclic templates are always of interest to both organic and medicinal chemists.[1]
Received October 1, 2009.
Address correspondence to Sodeh Sadjadi, Nuclear Fuel Cycle School, Nuclear Science and
Technology Research Institute, End of North Karegar Ave., P. O. Box 1439951113, Tehran, Iran.
E-mail: sadjadi.s.s@gmail.com
426

SYNTHESIS OF QUINOLINE AND QUINAZOLINE DERIVATIVES
427
Heterogeneous catalysis is an economically and ecologically important field in
catalysis research because these catalysts have many advantages: They are noncorro-
sive, environmentally benign, and present few disposal problems. They are also much
easier to separate from liquid products and they can be designed to give higher
activity, better selectivity, and longer catalyst lifetimes.[2–4] Because of these advan-
tages, research on chemical reactions using solid bases as catalysts has increased over
the past decade.[5] Many types of heterogeneous catalysts, such as alkaline earth
metal oxides, anion exchange resins, and various alkali metal compounds supported
on alumina or zeolite can catalyze many types of chemical reactions, such as isomer-
ization, aldol condensation, Knoevenagel condensation, Michael condensation,
oxidation, and transesterification.[6–11]
Copper oxide nanoparticles have been of considerable interest because of the
role of CuO in catalysis, gas sensors, and semiconductors.[12] CuO nanoparticles
were found to be effective catalysts for CO and NO oxidation as well as for the oxi-
dation of volatile organic chemicals such as methanol.[13] Very recently, Kantam et al.
reported the asymmetric hydrosilylation reaction of prochiral ketones with excellent
enantioselectivity,[14] synthesis of propargylamines via three-component coupling of
aldehydes, amines, and alkynes,[15] and direct asymmetric aldol reactions[16] cata-
lyzed by nanocrystalline copper oxide. CuO nanoparticles also find excellent applica-
tions as catalysts for coupling of diaryl diselenide with aryl halides,[17] alkyne–azide
cycloadditions,[18] and C-N cross coupling of amines with iodobenzene.[19]
As a consequence of our interest in aqueous media organic syntheses and in an
effort to design a solid base catalyst for the synthesis of fused heterocyclic structures,
we have determined that CuO nanoparticles efficiently catalyze the one-pot synthesis
of imidazo[1,2-a]quinoline and quinolino[1,2-a]quinazoline (Scheme 1).
In past decades, many methods have been developed to synthesize different
shapes of CuO nanostructures, such as the metal organic deposition technique,[20]
microwave irradiation,[21] sol-gel-like dip technique,[22] hydrothermal method,[23]
Scheme 1. One-pot synthesis of imidazo[1,2-a]quinoline and quinolino[1,2-a]quinazoline.

428
S. J. AHMADI, M. HOSSEINPOUR, AND S. SADJADI
reverse micelle-assisted rout,[24] chemical method,[25] and simple template-free
solution rout.[26]
Supercritical water hydrothermal synthesis (SCWHS) is among the most active
fields of green chemistry. It is a relatively simple and environmentally benign process.
We attempted the synthesis of copper oxide nanoparticles by batchwise super-
critical hydrothermal method. Advantages of this method over previous synthetic
approaches are shorter reaction time and possibility of performing a single-step
process.
The x-ray diffusion (XRD) pattern of nanosized particles is shown in Fig. 1. All
diffraction peaks of x-rays are indexed to the monoclinic crystal system of CuO. No
characteristic peaks are observed for other possible impurities, such as Cu(OH)2,
Cu2O, or Cu(OH)3NO3. The average size of the obtained CuO particle shown
in Fig. 2 is 5 nm. The crystallite size was also calculated by x-ray line-broadening
analysis using the Scherrer equation; we found that the average CuO crystallite size
was 8 nm. The mean value of surface area of CuO catalyst was 19.59 m2=g from
Brunauer–Emmet–Teller (BET) analysis.
The mechanism of formation of the CuO nanoparticle is this: When water is
heated up to its critical point (Tc ¼ 374 ꢀC, Pc ¼ 22.1 MPa), it changes from a polar
liquid to a fluid with a low dielectric constant. At the same time, the dissociation con-
stant of water (Kw) remarkably increases, giving rise to correspondingly increased
concentrations of Hþ and OHꢁ. From this point, the key role is played by OHꢁ ions
whose enhanced concentration according to Adschiri et al. leads to a rigorous
hydrolysis of the metal salts that is immediately followed by a dehydration step
(Scheme 2).
Adschiri et al. also pointed out that dielectric constant of water, the most
significant factor that controls the solvent power of water, declines at supercritical
Figure 1. XRD patterns of CuO particles prepared at supercritical condition and calcination of copper
nitrate trihydrate.

SYNTHESIS OF QUINOLINE AND QUINAZOLINE DERIVATIVES
429
Figure 2. Transmission electron micrographs of CuO nanoparticles.
Scheme 2. The mechanism of formation of the CuO nanoparticle.
condition, and hence the formed metal oxide can no longer stay in the aqueous phase
and must precipitate. As a result, at high temperature, supersaturation for precipi-
tation of metal oxide becomes greater, which consequently leads to creation of more
nucleation centers and thus formation of smaller particles (i.e., nanoparticles).[27]
First, the mixture of benzaldehyde, malononitrile, and enaminone 1a was cho-
sen as the model reaction to detect whether the use of CuO nanoparticle was
efficient. The reaction was carried out simply by mixing benzaldehyde, malononi-
trile, and enaminone 1a in water as solvent in the presence of a catalytic amount
of CuO nanoparticles (10 mmol%). The mixture was heated at 50 ꢀC for 35 min,
and the imidazo[1,2-a]quinoline 4a was obtained in 78% yield.
Encouraged by the result, we studied different reaction parameters, and the
results are summarized in Table 1. Only a trace amount of the target product was
Table 1. Formation of 4a with different basic catalysta
Entry
Catalyst
Catalyst (mmol%) Time (min) Yield (%)
1
2
3
4
5
6
None
—
30
50
50
50
50
180
35
60
60
50
65
Trace
96
73
CuO nanoparticles
Bulk CuO
MgO
78
81
Al2O3
ZnO
69
aReaction conditions: benzaldehyde (1 mmol), malononitrile (1 mmol), and
enaminone 1a (1 mmol), x mmol% catalyst; water; 50 ꢀC.

430
S. J. AHMADI, M. HOSSEINPOUR, AND S. SADJADI
observed when the mixture of benzaldehyde, malononitrile, and enaminone 1a was
heated under similar conditions in the absence of CuO nanoparticles even after heat-
ing for 3 h, thus highlighting the role of CuO nanoparticles as a promoter. We have
changed the amount of the CuO nanoparticles from 10 to 50 mmol%, finding that the
yield of product 4a was improved as the amount of CuO nanoparticles increased
from 10 to 30 mmol%. The yield did not improve when the amount of the catalyst
was further increased from 30 to 50 mmol%. Therefore, 30 mmol% of CuO nanopar-
ticles was considered to be most suitable.
The CuO nanoparticle catalyst was studied along with other known solid base
catalysts using the model reaction for the synthesis of the corresponding imidazo[1,2-a]
quinoline 4a. The results are summarized in Table 1. The results show that the three-
component reactions catalyzed by Al2O3, ZnO, and MgO proceed in longer reaction
times and afforded moderate product yields.
Afterward, the catalytic activity of the bulk CuO and CuO nanoparticle was
tested in the preparation of 4a. The obtained results are shown in Table 1. When
the model reaction was conducted with bulk CuO, a poor yield of the product
was obtained, while nano-CuO afforded excellent yields (Table 1).
The increased catalytic activity of nano-CuO over bulk CuO may be attributed
to the higher surface area of nano-CuO than bulk CuO as well as the higher surface
concentration of the reactive sites. As seen with other metal oxides, once they are
made into nanoparticles, their reactivity is greatly enhanced. This is thought to be
due to the morphological differences. Whereas larger crystallites have only a small
percentage of the reactive sites on the surface, smaller crystallites will possess a much
higher surface concentration of such sites.[28]
The formation of 4 is likely to proceed via initial condensation of aldehydes 2
with malononitrile 3 to afford 2-arylidenemalononitrile 5. The addition compound 5
Scheme 3. The reaction mechanism.

SYNTHESIS OF QUINOLINE AND QUINAZOLINE DERIVATIVES
431
Table 2. Synthesis of imidazo[1,2-a]quinoline and quinolino[1,2-a]quinazoline derivatives
Ref. mp
(ꢀC)[29]
Time
(min)
Yield
(%)
Entry
Enaminone
R1
Product (4)
Mp (ꢀC)
1
1a
C6H5
4a
299
299–300
294–296
35
40
96
93
2
1a
4-MeOC6H4
4b
294
3
1a
4-BrC6H4
4c
298
298–299
30
89
4
1b
C6H5
4d
298
298–299
35
91
5
1b
4-ClC6H4
4e
241
240–242
35
93
6
1b
4-MeC6H4
4f
298
298–300
45
89
to enaminones 1 then furnished the intermediate product 8, which upon intermole-
cular cyclization and dehydration gave rise to 4 (Scheme 3).
Then, we selected the optimized reaction condition to examine the universality
of this catalyst’s application. A series of aromatic aldehydes was selected to undergo

432
S. J. AHMADI, M. HOSSEINPOUR, AND S. SADJADI
Figure 3. IR spectra of CuO: (a) newly prepared and (b) used four times.
the condensation in the presence of a catalytic amount of CuO nanoparticles
(30 mmol%) in water at 50 ꢀC (Table 2). The results in Table 2 indicate that the aro-
matic aldehydes bearing different functional groups such as chloro, bromo, methyl,
or methoxy were able to undergo the condensation reaction.
The insolubility of the catalyst CuO in different organic solvents and water
provided an easy method for its separation from the product. Recycling experiments
were performed using the CuO nanoparticle catalyst for the synthesis of imidazo
[1,2-a]quinoline 4a. These recycling experiments show that the CuO nanoparticle
catalyzes the reaction with consistent activity even after four cycles. IR spectra of
the resulting solids indicate that the catalyst can be recovered without structural
degradation (Fig. 3).
In conclusion, we have reported herein several noteworthy features of a new
catalyst for the synthesis of imidazo[1,2-a]quinoline and quinolino[1,2-a]quinazoline
through the three-component condensation of benzaldehyde, malononitrile, and
enaminones 1a or 1b using CuO nanoparticles. This protocol offers many attractive
features such as greater yields and economic viability of the catalyst. The reaction
proceeds in water, and isolation of the catalyst is easily achieved. The catalyst is
recoverable and can be used in several runs without loss of catalytic activity. This
makes the method economic, benign, simple, and convenient for the synthesis of imi-
dazo[1,2-a]quinoline and quinolino[1,2-a]quinazoline, which are of biological and
medicinal importance.
EXPERIMENTAL
Preparation of the Ordinary Copper Oxide
To study physicochemical properties of the obtained CuO nanoparticles, the
bulk of CuO powder (nonnanometric) as comparison reference was prepared by a

SYNTHESIS OF QUINOLINE AND QUINAZOLINE DERIVATIVES
433
two-step calcination procedure. At first, crystalline copper nitrate trihydrate was
charged into a porcelain crucible and gently heated on a hot plate until most of
the hydration water was removed. Then, the crucible was transferred into a muffle
furnace and heated up to 400 ꢀC for 22 h, and at the end, the produced CuO product
was gently crushed and screened.
Preparation of the CuO-Nanoparticles Catalyst
Copper(II) nitrate trihydrate (Merck A G for synthesis) was used as the precur-
sor for synthesis of nano-CuO. Preparation of CuO took place in a stainless steel
(316 L) autoclave that was able to endure working temperature and pressure ꢁo3f
550 ꢀC and 610 atm, respectively. Concentration of Cu(NO3)2 was 0.05 mol ꢂ dm
,
and the heating period was about 2 h. Synthesis was carried out at 500 ꢀC to accel-
erate the hydrolysis reactions and thus shorten the fabrication period. To maintain
the safety margin, the 200-cm3 stainless steel autoclave was loaded with only
60–80 cm3 of the solution.
After removing it from the furnace, the autoclave was quenched by cold water
and CuO nanoparticles were recovered from the discharged solution by high-speed
centrifugation at 14,000 rpm for about 60 min. The produced nanoparticles were
then washed three times in the same centrifuge with ultrapure water and dried at
ambient temperature. Nanoparticles were characterized by XRD (Philips PW
1800) and transmission electron microscope (TEM) (LEO 912AB) tests.
General Procedure for the Synthesis of Enaminones 1a and b
A mixture of 5,5-dimethyl-1,3-cyclohexanedione (1 mmol), amine (1 mmol),
and CuO nanoparticles (30 mmol%) was refluxed in 5 mL water for 45 min. Upon
completion, as monitored by thin-layer chromatography (TLC), the reaction mixture
was cooled to room temperature. The solid products were filtered and diluted with
chloroform, and the catalyst was removed by simple centrifugation. After evapor-
ation of solvent, the resulting solid was recrystallized from EtOH to give the pure
products (1a and b).
General Procedure for the Synthesis of Compound 4
A mixture of aldehyde 2 (1 mmol), malononitrile 3 (1 mmol), enaminones 1a or
1b (1 mmol), and CuO nanoparticles (30 mmol%) in H2O (5 mL) was heated at 50 ꢀC
for 30–45 min (the progress of the reaction being monitored by TLC using n-hexane=
ethyl acetate as an eluent, 2:3). Upon completion of the reaction, the reaction
mixture was filtered to isolate the solid product. Then solid product was diluted with
chloroform, and the catalyst was removed by simple centrifugation (the catalyst is
not soluble in chloroform). After evaporation of solvent, more purification was
obtained by recrystallization from ethanol.
Spectral data of the products described in this article are the same as those
reported in a previously published paper.[29]

434
S. J. AHMADI, M. HOSSEINPOUR, AND S. SADJADI
Catalyst Recovery and Recycling
After completing the model reaction, the catalyst was separated, washed three
times with 10-ml portions of chloroform, dried at 150 ꢀC for 1 h, and subjected to a
second run of the reaction process with the same substrate.
ACKNOWLEDGMENT
The authors are thankful to the Nuclear Science and Technology Research
Institute for the partial financial support.
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