Fe3O4 nanoparticle-supported copper(I): Magnetically recoverable and reusable catalyst for the synthesis of quinazolinones and bicyclic pyrimidinones

Article abstract of DOI:10.1002/aoc.2902

A highly efficient, easily recoverable and reusable Fe₃O ₄ magnetic nanoparticle-supported Cu(I) catalyst has been developed for the synthesis of quinazolinones and bicyclic pyrimidinones. In the presence of supported Cu(I) catalyst (10 mol%), amidines reacted with substituted 2-halobenzoic acids and 2-bromocycloalk-1-enecarboxylic acids to generate the corresponding N-heterocycle products in good to excellent yields at room temperature in DMF. In addition, the supported Cu(I) catalyst could be recovered at least 10 times without significant loss of its catalytic activity. Copyright

Full text of DOI:10.1002/aoc.2902

Full Paper
Received: 8 May 2012
Revised: 9 June 2012
Accepted: 25 June 2012
Published online in Wiley Online Library
(wileyonlinelibrary.com) DOI 10.1002/aoc.2902
Fe3O4 nanoparticle-supported copper(I):
magnetically recoverable and reusable catalyst
for the synthesis of quinazolinones and
bicyclic pyrimidinones
Lin Yua, Min Wanga, Pinhua Lia and Lei Wanga,b*
A highly efficient, easily recoverable and reusable Fe3O4 magnetic nanoparticle-supported Cu(I) catalyst has been developed
for the synthesis of quinazolinones and bicyclic pyrimidinones. In the presence of supported Cu(I) catalyst (10 mol%), amidines
reacted with substituted 2-halobenzoic acids and 2-bromocycloalk-1-enecarboxylic acids to generate the corresponding
N-heterocycle products in good to excellent yields at room temperature in DMF. In addition, the supported Cu(I) catalyst could be
recovered at least 10 times without significant loss of its catalytic activity. Copyright © 2012 John Wiley & Sons, Ltd.
Supporting information may be found in the online version of this article.
Keywords: supported Cu(I) catalyst; magnetic nanoparticles; amidines; 2-halobenzoic acids; quinazolinones
surface for immobilization of catalysts. In particular, as robust
and high-surface-area heterogeneous catalyst supports, Fe3O4
Introduction
The use of efficient and clean catalysts is becoming a hot
research field for chemists because it represents a new strategy
to meet the challenges of energy and sustainability. Although
homogeneous catalysts have many advantages, such as high
turnover number, good activity and selectivity, and are widely used
in a variety of industries, separation of the soluble catalyst from the
product and reaction medium remains difficult, especially for
expensive and/or toxic heavy metal complex. Furthermore, it is
essential to remove toxic metals from the final product because
metal contamination is highly regulated, especially in the drug
and pharmaceutical industry. Catalyst recovery and reuse are the
two most important features for many green synthetic methods.
Heterogenization of the existing homogeneous catalysts, thus
creating a heterogeneous catalytic system, has become one
powerful way to solve these problems.[1] Over the past few
decades, various inorganic and organic supports have been
explored, such as mesoporous silica,[2] ionic liquids[3] and poly-
mers,[4] and the grafting of such supports with homogeneous
catalysts often provides catalyst systems that can be efficiently
recycled and reused by filtration or liquid/liquid extraction while
keeping the inherent catalytic activity.[5]
nanoparticles have successfully demonstrated the application of
various strategies.[9]
Nitrogen-containing heterocycles, especially quinazolinone
and bicyclic pyrimidinone derivatives, represent a predominant
structural motif in a wide array of biologically active natural
compounds, pharmaceuticals and organic functional materials.[10]
There is therefore considerable attention to the development of
practical methods for the synthesis of this structural element.
The traditional synthetic routes to such compounds depend
on the common starting materials ortho-amino- or -nitrobenzoic
acid derivatives, which are not readily available or are difficult to
prepare.[11] Alternatively, Fu[12] and others[13] have developed
efficient copper-catalyzed Ullmann N-arylations for the preparation
of N-heterocycles. Following that, Fu described an iron-catalyzed
cascade synthesis of 1,2,4-benzothiadiazine 1,1-dioxide and
quinazolinone derivatives.[14] In 2010, Liu et al. developed an
iron/copper co-catalyzed synthesis of 2-methylquinazolin-4(3H)-
one under microwave irradiation.[15] Most recently, Fu[16] also
reported a novel and useful domino method for construction
of quinazolinones using readily available a-amino acids as the
nitrogen-containing motifs. All of these protocols use homogeneous
Recently, new smart supports – magnetic nanoparticles (MNPs) –
have emerged and have great potential for catalyst recovery,
because magnetic separation from the reaction mixture with
an external permanent magnet is typically simpler and more
effective than filtration or centrifugation as it prevents loss of
the catalyst.[6] In recent years, fabrication of core–shell magnetic
nanoparticles made up of a magnetic iron oxide core coated by
a layer of cross-linked polymer[7] or silica[8] shell has been the
subject of research, since such materials combine the stabilization
of magnetic nanoparticles by preventing aggregation of oxide
cores together with the possibility of further functionalizing the
*
Correspondence to: L. Wang, Department of Chemistry, Huaibei Normal
University, Huaibei, Anhui 235000, People’s Republic of China. Email:
leiwang@chnu.edu.cn
a Department of Chemistry, Huaibei Normal University, Anhui 235000, People’s
Republic of China
b State Key Laboratory of Organometallic Chemistry, Shanghai Institute of
Organic Chemistry, Chinese Academy of Sciences, Shanghai 200032, People’s
Republic of China
Appl. Organometal. Chem. (2012),
Copyright © 2012 John Wiley & Sons, Ltd.

Lin Yu et al.
catalysts. Engaged in the development of greener and sustain-
able pathways for organic transformations,[17] herein we wish
to report an efficient magnetically recoverable and reusable
Fe3O4 nanoparticle-supported copper(I) catalyst and its application
in cascade reactions of amidines with substituted 2-halobenzoic
acids and 2-bromocycloalk-1-enecarboxylic acids to synthesize
N-heterocycles. It was found that the Fe3O4 nanoparticle-supported
copper(I) catalyst exhibits high reactivity and a wide range of
substrate applicability. Recovery of the catalyst by decantation of
the reaction mixture in the presence of an external magnet is easy
and efficient. We demonstrated that it is possible to recover and
reuse this grafted catalyst at least 10 times without significant loss
of its reactivity (Scheme 1).
by repeated washing with H2O (5 Â 2.5 ml) until the pH of the
solution reached 7, and then washed with ethanol (2 Â 3.0 ml)
and CH3CN (2 Â 3.0 ml), respectively. The obtained nanosphere
was subsequently added to CuI (0.50 mmol) in CH3CN (10.0 ml)
solution, which ultrasonically dispersed until no solid was
observed. The mixture was shaken at room temperature for 4 h
until the solution became clarified. Then the solid catalyst was
magnetically separated, and the solid was washed thoroughly with
THF (3 Â 3.0 ml) and CH3CN (2 Â 3.0ml), and dried under vacuum
at 50ꢀC for 3 h. The Fe3O4 nanoparticle-supported Cu(I) catalyst,
Catal. A, was obtained with a loading of copper 0.158mmolgÀ1
determined via inductively coupled plasma (ICP) analysis. IR (KBr,
cmÀ1): nO–H and nN–H = 3419 (br), nC–H = 2935, nSi–O = 1056.
Typical Procedure for the Cascade Reaction of Acetamidine
with 2-Iodobenzoic Acid to Synthesize Quinazolinone 3a
Experimental
General Methods
Under nitrogen atmosphere, a sealable reaction tube was charged
with 2-iodobenzoic acid (1a, 0.50 mmol), acetamidine hydrochlo-
ride (2a, 0.75 mmol), Catal. A (317 mg, containing Cu 0.05 mmol),
Cs2CO3 (1.0mmol) and DMF (3.0ml). The mixture was shaken at
room temperature for 10 h. After magnetic separation of the
catalyst, the organic material was extracted with ethyl acetate.
The resulting solution was dried by Na2SO4, then concentrated
under reduced pressure. The residue was purified by flash chro-
matography on silica gel (eluent: petroleum ether–ethyl acetate,
1:1–1:3, v/v) to give the desired product quinazolinone 3a (white
solid, 78 mg, 97% yield).
All reactions were carried out under nitrogen atmosphere. All chem-
ical reagents were purchased from commercial suppliers and used
without further purification. 1 H NMR and 13 C NMR spectra were
measured on a Bruker Avance NMR spectrometer (400 MHz and
100 MHz, respectively) with DMSO-d6 or CDCl3 as solvent and
recorded in ppm relative to internal tetramethylsilane standard.
The peak patterns are indicated as follows: s, singlet; d, doublet;
t, triplet; m, multiplet; q, quartet. The coupling constants, J, are
reported in hertz (Hz). IR spectra were obtained by using a
Nicolet NEXUS 470 spectrophotometer. High-resolution mass
spectroscopic data of the products were collected on a Waters
Micromass GCT instrument.
The following compounds have been characterized by compar-
ing their 1 H and 13 C spectral data (see supporting information)
with those reported in the literature:
Preparation of Fe3O4 Nanoparticle-Supported Copper(I)
catalyst, Catal. A
2-methylquinazolin-4(3 H)-one (3a)[12a]
2-phenylquinazolin-4(3 H)-one (3b)[12a]
2-cyclopropylquinazolin-4(3 H)-one (3c)[12a]
Fe3O4 magnetic nanoparticles (0.60 g, with an average diameter
of 20 nm, purchased from Aldrich) were diluted with 8.0 ml
deionized water and 40.0 ml i-PrOH, and the mixture was sonicated
for approximately 30 min (the average diameter of Fe3O4 was
about 10 nm according to the transmission electron microscope
(TEM) image). To this well-dispersed magnetic nanoparticle solu-
tion, 1.0 g tetraethyl orthosilicate and 0.60 g [3-(2-aminoethyl)
aminopropyl]trimethoxysilane in 2.0 ml i-PrOH was slowly added
and stirred for half an hour. Then 1.5 ml NH3.H2O was added to
the mixture drop by drop with mechanical stirring for a further
5 h at room temperature. The collected material was purified
6-fluoro-2-methylquinazolin-4(3 H)-one (3d)[18]
6-fluoro-2-phenylquinazolin-4(3 H)-one (3e)[19]
7-methoxy-2-methylquinazolin-4(3 H)-one (3 g)[20]
7-methoxy-2-phenylquinazolin-4(3 H)-one (3 h)[20]
2,8-dimethylquinazolin-4(3 H)-one (3j)[21]
8-methyl-2-phenylquinazolin-4(3 H)-one (3 k)[21]
2-methyl-5,6,7,8-tetrahydronquinazolin-4(3 H)-one (3 m)[12o]
2-phenyl-5,6,7,8-tetrahydronquinazolin-4(3 H)-one (3n)[12o]
2-cyclopropyl-5,6,7,8-tetrahydronquinazolin-4(3H)-one(3o)[12o]
2-methyl-6-nitroquinazolin-4(3H)-one (3p)[12a]
Scheme 1. Synthesis of magnetic nanoparticle-supported copper(I) catalyst and its application in the synthesis of quinazolinones and bicyclic pyrimi-
dinones: (a) Si(OEt)4/NH3.H2O; (b) H2NCH2CH2NHCH2CH2CH2Si(OEt)3/toluene; (c) CuI/CH3CN
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Fe3O4 nanoparticle-supported copper(I)
Table 1. Optimization of the reaction conditionsa
I
I
Entry
Base
Solvent
Yieldb (%)
1
Cs2CO3
Na3PO4
K3PO4
DMF
97
90
2
DMF
3
DMF
85
4
Na2CO3
K2CO3
KF
DMF
80
5
DMF
88
6
DMF
31
7
NaOAc
Et3N
DMF
43
8
DMF
30
9
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
MeOH
THF
Trace
Trace
Trace
77
10
11
12
13
14
15
16
17
18
19
20
Dioxane
EtOH
i-PrOH
CH3CN
Toluene
DMA
DMSO
DMF
69
88
83
75
85
63c
72d
76e
DMF
DMF
aReaction conditions: 2-iodobenzoic acid (1a, 0.50 mmol), acetamidine hydrochloride (2a, 0.75 mmol), Fe3O4@SiO2–Cu(I) (Catal. A, 317 mg,
containing Cu 0.05 mmol), base (1.0 mmol) in solvent (3.0 ml) at room temperature under nitrogen atmosphere for 10 h.
bIsolated yield.
cFe3O4@SiO2–Cu(I) catalyst (159 mg, containing Cu 0.025 mmol) was added.
dCs2CO3 (0.50 mmol) was added.
eReaction time was 6 h.
6-nitro-2-phenylquinazolin-4(3 H)-one (3q)[12a]
2-cyclopropyl-6-nitroquinazolin-4(3 H)-one (3r)[12a]
1.97À1.91 (m, 1 H, -CH), 1.11À0.97 (m, 4 H, -CH2); 13 C NMR
(100 MHz, DMSO-d6): d = 162.4, 158.2, 147.9, 134.8, 134.7,
125.0, 123.8, 120.9, 17.3, 13.9, 10.1. Elemental analysis: Calcd
for C12H12N2O: C, 71.98; H, 6.04; N, 13.99%. Found: C, 71.59; H,
5.92; N, 13.78%. HRMS (EI) ([M]+). Calcd for C12H12N2O:
200.0950. Found 200.0949.
2-Cyclopropyl-6-fluoroquinazolin-4(3 H)-one (3f). White solid,
m.p. 253.6À254.3ꢀ. 1 H NMR (400 MHz, DMSO-d6): d = 12.46
(s, br, 1 H, N-H), 7.65À7.62 (m, 1 H, Ar-H), 7.51À7.46 (m, 2 H, Ar-H),
1.94À1.90 (m, 1 H, -CH), 1.10À0.97 (m, 4 H, -CH2); 13 C NMR
(100MHz, DMSO-d6): d = 161.4, 159.6 (d, JC–F = 242.8 Hz), 158.8,
146.4, 129.6, 122.9 (d, JC–F = 20.6 Hz), 122.1, 110.6 (d, JC–F =22.7Hz),
13.8, 9.8. Elemental analysis: Calcd for C11H9N2OF: C, 64.70; H, 4.44; N,
13.72%. Found: C, 64.43; H, 4.70; N, 13.68%. HRMS (EI) ([M]+). Calcd
for C11H9N2OF: 204.0699. Found 204.0697.
2-Cyclopropyl-7-methoxyquinazolin-4(3 H)-one (3i). White
solid, m.p. 237.2À239.6 ꢀC. 1 H NMR (400 MHz, DMSO-d6):
d = 12.30 (s, br, 1 H, N-H), 7.41À7.38 (m, 2 H, Ar-H), 7.29À7.26
(m, 1 H, Ar-H), 3.80 (s, 3 H, -OCH3), 1.94À1.88 (m, 1 H, -CH),
1.05À0.93 (m, 4 H, -CH2); 13 C NMR (100 MHz, DMSO-d6):
d = 161.9, 157.2, 156.9, 143.9, 128.5, 124.1, 121.7, 106.2, 55.9,
13.7, 9.5. Elemental analysis: Calcd for C12H12N2O2: C, 66.65; H,
5.59; N, 12.96%. Found: C, 66.93; H, 5.28; N, 12.80%. HRMS (EI)
([M]+). Calcd. for C12H12N2O2: 216.0899. Found 216.0898.
Results and Discussion
The magnetic nanoparticle-supported Cu(I) catalyst was prepared
according to the synthetic route in Scheme 1. The Fe3O4 with an
average diameter of 10 nm (TEM result) after sonication was coated
with silica as shell to produce Fe3O4@SiO2 nanoparticles.[22] The
obtained silica coating not only protects the magnetic cores but
can also be easy modified with other functional groups through
the reaction of OH groups on the surface. TEM images of the
Fe3O4@SiO2 show the core–shell structure of the particles, and
the silica coating has a uniform thickness of 10 nm. Treatment of
the silica-coated nanoparticles with excess N-(3-(triethoxysilyl)
propyl)ethane-1,2-diamine in toluene at refluxing temperature
for 24 h afforded silica nanospheres functionalized with 1,2-
diamine groups. The magnetically Fe3O4 nanoparticle-supported
Cu(I) catalyst was obtained by simply dissolving CuI in CH3CN and
treating it with the above amine-functionalized Fe3O4@SiO2. The
2-Cyclopropyl-8-methylquinazolin-4(3 H)-one (3 l). White solid,
m.p. 227.6À229.4 ꢀC. 1 H NMR (400 MHz, DMSO-d6): d = 12.33
(s, br, 1 H, N-H), 7.85 (d, J = 4.0 Hz, 1 H, Ar-H), 7.49 (d, J = 8.0 Hz,
1 H, Ar-H), 7.20 (t, J = 8.0 Hz, 1 H, Ar-H), 2.37 (s, 3 H, -CH3),
Appl. Organometal. Chem. (2012),
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Lin Yu et al.
Table 2. The cascade reactions for the preparation of quinazolinone and bicyclic pyrimidinone derivativesa
Entry
1
1
2
Product, 3
Yield (%)b
97
1a
1a
2a
2b
3a
3b
2
3
99
99
1a
2c
3c
4
5
1b
1b
2a
2b
3a
3b
90
95
6
1b
2c
3c
94
7
8
1c
1c
2a
2b
3d
3e
84
90
9
1c
2c
2a
3f
93
81
10
1d
3g
11
12
1d
1d
2b
2c
3h
3i
92
98
(Continues)
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Fe3O4 nanoparticle-supported copper(I)
Table 2. (Continued)
13
1e
1e
2a
2b
3j
73
82
14
15
3k
1e
2c
3l
87
16
17
1f
1f
2a
2b
3m
3n
72
78
18
1f
2c
3o
86
19
20
1g
1g
2a
2b
3a
3b
74c
85c
21
1g
2c
3c
90c
22
23
1h
1h
2a
2b
3p
3q
68c
76c
24
1h
2c
3r
80c
a
Reaction conditions: 1 (0.50 mmol), 2 (0.75 mmol), Fe3O4@SiO2–Cu(I) (Catal. A, 317 mg, containing Cu 0.05 mmol), Cs2CO3 (1.0 mmol), DMF (3.0 ml)
at room temperature under nitrogen atmosphere for 10 h.
Isolated yield.
b
c
Reaction temperature was 50 ꢀC.
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Lin Yu et al.
Table 3. Recycling of Fe3O4 nanoparticle-supported Cu(I) Catal. Aa
Run
Yieldb (%)
Run
Yieldb (%)
1
2
3
4
5
97
97
96
97
95
6
7
94
93
94
94
93
8
9
10
aReaction conditions: 2-iodobenzoic acid (1a, 0.50 mmol), acetamidine hydrochloride (2a, 0.75 mmol), reused Fe3O4@SiO2–Cu(I) (Catal. A, 317 mg,
containing Cu 0.05 mmol), Cs2CO3 (1.0 mmol), DMF (3.0 ml) at room temperature under nitrogen atmosphere for 10 h.
bIsolated yields.
generated Catal. A was found to be with a loading of 0.158 mmol
of Cu gÀ1 determined via ICP analysis. X-ray diffraction measure-
ments of Catal. A exhibit diffraction peaks corresponding to the
typical spinal magnetite structure; the diffraction peak of the lay-
ered amorphous silica was not obvious and no peaks characteristic
for Cu(0) nanoparticles were observed.
2-iodo- and 2-bromobenzoic acids in the cascade reactions under
the same reaction conditions, while 2-iodobenzoic acid showed
the highest reactivity (Table 2, entries 1–3). We were delighted that
moderate to good yields were obtained when the reaction temper-
ature was increased to 50 ꢀC in the reactions of 2-chlorobenzoic
acid and 2-chloro-5-nitrobenzoic acid with amidines (Table 2,
entries 19–24). Generally, the reaction efficiency was insensitive
to the electronic properties of the groups on the phenyl ring of
2-halobenzoic acid 1, while unsubstituted 2-halobenzoic acids
gave higher yields than that of substituted ones, whether electron-
withdrawing or electron-donating groups (Table 2, entries 4 vs. 7,
10 and 13; 5 vs. 8, 11 and 14). The hindrance of the phenyl ring of
1 had a slight effect on the efficiency (Table 2, entries 13–15). More-
over, 2-bromocyclohex-1-enecarboxylic acid could also react with
amidines under the present reaction conditions, and bicyclic
pyrimidinone derivatives were isolated in good yields (Table 2,
entries 16–18). As for amidines, it is obvious that benzimidamide
and cyclopropanecarboximidamide exhibited higher reactivity than
acetimidamide. For example, the reaction of 2-iodobenzoic acid with
benzimidamide or cyclopropanecarboximidamide, or 2-bromo-4-
methoxybenzoic acid with cyclopropanecarboximidamide, pro-
vided the corresponding quinazolinones in almost quantitative
yields (Table 2, entries 2, 3 and 12).
To evaluate the efficiency of supported Cu(I) catalyst, it was
tested by means of the cascade reaction of 2-halobenzoic acid
with amidine (Table 1). To our delight, the reaction of 0.50 mmol
of 2-iodobenzoic acid (1a) with 0.75 mmol acetamidine hydro-
chloride (2a) in DMF in the presence of Catal. A (10 mol%,
relative to the amount of 1a) using 2 equiv. of Cs2CO3 as the base
afforded the quinazolinone 3a in 98% yield (Table 1, entry 1). We
then began the following investigation on the model reaction to
optimize the other reaction parameters, including base and
solvent, and the results are summarized in Table 1. It is evident
that Cs2CO3 is the most effective base for the model reaction
(Table 1, entry 1), and lower yields were obtained by using
Na3PO4, K3PO4, Na2CO3 or K2CO3 as base (Table 1, entries 2–5).
Poor results were observed using KF, NaOAc or Et3N (Table 1,
entries 6–8). The effect of solvents on the reaction was also
screened. Only trace amounts of quinazolinone 3a were
observed when the reaction was carried out in MeOH, THF or
dioxane (Table 1, entries 9–11) although the reactions in EtOH,
i-PrOH, CH3CN, toluene, N,N-dimethyl acetamide (DMA) and
DMSO gave the desired product in moderate yields (Table 1,
entries 12–17). Decreasing the amount of catalyst or base or
shortening the reaction time also decreased the yield (Table 1,
entries 18–20). After surveying a variety of catalysts, bases and
solvents, we found that the combination of 10 mol% Fe3O4
nanoparticle-supported Catal. A and 2 equiv of Cs2CO3 in DMF
at room temperature for 10 h served as the optimal conditions
for this transformation.
Recovery of the catalyst is easy and efficient. After the reaction
was completed, Fe3O4 nanoparticle-supported Cu(I) Catal. A was
recovered by decantation of the reaction mixture in the presence
of an external magnet. The catalyst was then washed with ethyl
acetate, dried under high vacuum, and used directly for the next
round of reaction without further purification. For the reaction of
2-iodobenzoic acid with acetamidine, the supported copper
catalyst could be recycled and reused for 10 consecutive trials
without any significant loss in activity (Table 3).
Next, a variety of substituted 2-halobenzoic acids with amidines
were examined under the optimized reaction conditions, and the
results are listed in Table 2. In all cases, the reactions took place
smoothly, giving quinazolinone derivatives in high yields. The most
probable reason for the higher reactivity of Fe3O4 nanoparticle-
supported copper(I) catalyst is that nanoparticles have a much
larger surface area to volume ratio, which can provide a higher
catalytic activity. As expected, due to the relative higher strength
of C-Cl bond, 2-chlorobenzoic acid showed lower reactivity than
Conclusions
We have developed a Fe3O4 nanoparticle-supported copper(I)
catalyst which exhibits excellent reactivity in the cascade reactions
of 2-halobenzoic acids and 2-bromocyclohex-1-enecarboxylic acid
with amidines. The reactions generated the corresponding quina-
zolinone and bicyclic pyrimidinone derivatives in good to excellent
yields. Magnetically, nanocatalyst has a much larger surface area to
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Fe3O4 nanoparticle-supported copper(I)
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volume ratio, which can provide a higher catalytic activity. Recovery
of the catalyst by decantation of the reaction mixture in the
presence of an external magnet is easy and efficient. The catalyst
was recycled over ten times in reactions without any obvious loss
in its activity.
Acknowledgments
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This work was financially supported by the National Science Foun-
dation of China (nos. 21172092, 20102039 and 20972057) and the
Key Project of Science and Technology of Anhui Education Depart-
ment, China (no. KJ2012A253).
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