Catalyst-free synthesis of quinazoline derivatives using low melting sugar-urea-salt mixture as a solvent

Article abstract of DOI:10.1039/c2gc35258c

Low melting mixture of maltose-dimethylurea (DMU)-NH₄Cl was found to be an inexpensive, non-toxic, easily biodegradable and effective reaction medium in the catalyst-free synthesis of quinazoline derivatives. This simple and efficient method fu

Full text of DOI:10.1039/c2gc35258c

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PAPER
Catalyst-free synthesis of quinazoline derivatives using low melting
sugar–urea–salt mixture as a solvent†
Zhan-Hui Zhang,* Xiao-Nan Zhang, Li-Ping Mo, Yong-Xiao Li and Fei-Ping Ma
Received 21st February 2012, Accepted 13th March 2012
DOI: 10.1039/c2gc35258c
Low melting mixture of maltose–dimethylurea (DMU)–NH4Cl was found to be an inexpensive, non-
toxic, easily biodegradable and effective reaction medium in the catalyst-free synthesis of quinazoline
derivatives. This simple and efficient method furnished the corresponding quinazolines in high yields via
one-pot three-component reaction of 2-aminoaryl ketones, aldehyde, and ammonium acetate under
aerobic oxidation conditions.
therapeutic properties such as antibacterial,15 anti-inflamma-
Introduction
tory,16 antiplasmodial,17 antitumor,18 antimicrobial and anti-
oxidant.19 In addition, they have also been used as
photochemotherapeutic agents,20 DNA-gyrase, JAK2, PDE5,
and EGFR tyrosine kinase inhibitors,21 as well as CB2 receptor
agonists.22 Consequently, wide demands of diverse quinazoline
derivatives in various fields have promoted the development of
practical and diversified synthetic methods. A variety of pro-
cedures have been reported, such as (i) copper-catalyzed cascade
coupling of 2-bromobenzaldehyde with acetamidine hydrochlo-
ride;23 (ii) cyclization of substituted [2-(methyleneamino)
phenyl] methanoneoximes by photochemical methods;24 (iii) the
reaction of N-imidoyliminophosphorane and aldehyde using con-
ventional microwave oven;25 (iv) copper-catalyzed alkynylation
and cyclization of N-phenylbenzamidines;26 (v) tandem reaction
from 2-aminobenzophenones and benzylic amines followed by
sp3 C–H functionalization;27 (vi) the condensation of aldehydes
with 2-aminobenzylamine using sodium hypochlorite28 or
Solvent choice is a crucial step in organic synthesis. Despite a
small number of organic reactions which can be performed in
the solid state or solvent-free conditions, these approaches are
restricted due to the easy formation of undesired side products
and the difficult heat flow control.1 In the last decade, many
promising media have appeared as innocuous solvents, such as
water,2 ionic liquids,3 supercritical fluids,4 polyethylene glycol,5
glycerol,6 and perfluorinated solvents.7 However, the use of
these solvents is still limited by many problems: some com-
pounds, substrates, or reagents have a poor solubility or stability
in water; some ionic liquids lack of toxicity and biocompatibility
data with high prices; sophisticated equipment is usually
required when perfluorinated solvents are employed.
In recent years, low melting mixtures consisting of carbo-
hydrates, urea and inorganic salts have been introduced as new
alternative sustainable solvents for organic transformations.8
These solvents have been applied to Stille,9 Diels–Alder,10
Heck, and cycloaddition reactions.11 The synthesis of 5-hydroxy-
methylfurfural,12 glycosyl ureas,13 and 3,4-dihydropyrimidin-2-
ones,14 have been reported by using of low melting mixture of
carbohydrates, urea and inorganic salts as solvents. The peculiar
physical and chemical properties of low melting mixtures, such
as polarity, low toxicity, non-volatility, biodegradability, low
cost, thermal stability, and ready availability from bulk renewable
resources without any further modification, prompted us to
extend their use as green solvents in organic synthesis.
29
MnO2 as oxidant; (vii) copper-catalyzed Ullmann N-arylation
coupling process;30 (viii) microwave irradiations of 2-(ami-
noaryl)alkanone O-phenyl oximes and carbonyl compounds;31
Nevertheless, those methods suffer from limitations of substrate
generality, the availability of starting materials, multistep syn-
thesis, use of expensive catalyst, ligand or additives, lower
product yields, and harsh conditions. Therefore, the design of
improved and environmentally benign approaches that allow for
the rapid, cost-effective synthesis of quinazolines from readily
available precursors would be highly desired.
Quinazoline is one of the most important nitrogen hetero-
cycles commonly found in a wide variety of natural products,
pharmaceutical molecules, and functional materials. Quinazoline
derivatives have been reported to possess diverse biological and
One such way is to use multicomponent reactions (MCRs)
that can construct complex molecules from common starting
materials in an one-pot manner, which provide significant advan-
tages over conventional linear-type syntheses due to their
flexible, convergent and atom efficient nature. These reactions
can avoid time-consuming and costly processes for purification
of the intermediates and tedious steps of protection and deprotec-
tion of functional groups, thereby enhancing the greenness of
transformations. Thus, MCRs have become an important area of
research in organic, medicinal and combinatorial chemistry for
College of Chemistry & Material Science, Hebei Normal University,
Shijiazhuang 050024, People’s Republic of China. E-mail:
zhanhui@126.com; Fax: +86 31189632795
†Electronic supplementary information (ESI) available: 1H NMR and
13C NMR spectra of all compounds. See DOI: 10.1039/c2gc35258c
1502 | Green Chem., 2012, 14, 1502–1506
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Table 1 Three-component reaction of 2-amino-benzophenone, 4-
nitrobenzaldehyde and ammonium acetate in various solventsa
Scheme 1 Synthesis of quinazoline derivatives in maltose–DMU–
NH4Cl.
Temp
(°C)
Time
(min)
Yield
(%)
assembling compounds and lead to the identification of bioactive
ones.32 If such reactions could be run in innocuous solvents,
they would comply with most of the green chemistry
principles.33
As part of our continuing interest in developing efficient and
environmental benign synthetic methodologies,34 herein, we
describe the use of low melting mixtures of maltose–dimethyl-
urea (DMU)–NH4Cl as a green solvent for the synthesis of qui-
nazoline derivatives via a one-pot three-component reaction of
2-aminoaryl ketones, aldehydes, and ammonium acetate under
aerobic oxidation conditions (Scheme 1).
Entry Solvent
1
2
EtOH
H2O
Reflux
Reflux
90
Reflux
Reflux
Reflux
Reflux
Reflux
65
180
180
180
180
180
180
180
600
200
300
300
Trace
Trace
10
19
20
3
4
No
CH3CN
5
6
DMSO
DMF
13
7
8
9
Toluene
18
CH3COOHb
Citric acid–DMU (40 : 60)
5035
85
10
11
D-(−)-Fructose–DMU (70 : 30) 71
75
82
L-(+)-Tartaric acid–DMU
(30 : 70)
70
90
89
88
84
90
12
13
14
15
L-(+)-Tartaric acid–choline
chloride (50 : 50)
Mannose–DMU–NH4Cl
(50 : 40 : 10)
Lactose–DMU–NH4Cl
(50 : 40 : 10)
Maltose–DMU–NH4Cl
(50 : 40 : 10)
250
250
250
150
89
82
86
92
Results and discussion
The initial attempt was guided by the model reaction of 2-amino-
benzophenone with 4-nitrobenzaldehyde and ammonium acetate
in different solvents under aerobic oxidation conditions, and the
results are summarised in Table 1. Only a trace amount of quina-
zoline (4ag) was detected when the reactions were carried out in
EtOH or H2O. Poor to low yields were observed when the reac-
tion proceeded in CH3CN, DMF, DMSO, toluene or in neat con-
ditions (Table 1, entries 3–7). From an environmental point of
view, these procedures do not meet the requirement of green
chemistry, although a good result was obtained in refluxing
acetic acid, where a mixture of dihydroquinazoline and quinazo-
line was formed.35 Considering the fact that sugar–urea–salt mix-
tures are high polar, have low melting temperatures (65–90 °C),
and have small vapour pressures, like ionic liquids, they can be
used as an alternative green solvent. The model reaction was
carried out in various melt mixtures, including citric acid–DMU,
D-(−)-fructose–DMU, L-(+)-tartaric acid–DMU, L-(+)-tartaric
acid–choline chloride, mannose–DMU–NH4Cl, lactose–DMU–
NH4Cl, and maltose–DMU–NH4Cl at their minimal melting
temperature. As expected, the reaction proceeded in these melt
mixtures, and the corresponding product was obtained in
75–92% yields (Table 1, entries 9–15). Further investigation of
this reaction was achieved by using these melt mixtures at 90 °C.
Maltose–DMU–NH4Cl was found to be superior to other melts,
which gave 93% yield of the product. In addition, other eutectic
mixture such as choline chloride–urea was also examined and
an 85% yield of the desired product was obtained (Table 1,
entry 22).
16
17
18
Citric acid–DMU (40 : 60)
150
150
150
90
80
85
D-(–)-Fructose–DMU (70 : 30) 90
L-(+)-Tartaric acid–DMU
(30 : 70)
90
90
90
90
90
90
90
90
90
90
84
19
20
21
22
23
24
25
26
27
28
Mannose–DMU–NH4Cl
(50 : 40 : 10)
Lactose–DMU–NH4Cl
(50 : 40 : 10)
Maltose–DMU–NH4Cl
(50 : 40 : 10)
Choline chloride–urea
(54.1 : 45.9)
Maltose–DMU–NH4Cl
(50 : 40 : 10)
Maltose–DMU–NH4Cl
(50 : 40 : 10)
Maltose–DMU–NH4Cl
(50 : 40 : 10)
Maltose–DMU–NH4Cl
(50 : 40 : 10)
150
150
150
150
150
150
150
150
150
180
86
88
93
85
64c
70d
65e
78f
55g
90h
Maltose–DMU–NH4Cl
(50 : 40 : 10)
Maltose–DMU–NH4Cl
(50 : 40 : 10)
a Reaction conditions: 2-aminobenzophenone (1 mmol), 4-
nitrobenzaldehyde (1 mmol), ammonium acetate (1 mmol), solvent
(1.5 g). b The reaction of 2-aminobenzophenone, benzaldehyde and
ammonium acetate in refluxing acetic acid gave dihydroquinazoline and
quinazoline in a combined yield of 50%. c NH4F was used. d (NH4)2SO4
was used. e (NH4)2CO3 was used. f Urea was used. g The reaction was
carried out in the absence of ammonium acetate. h 50 mmol scale.
We also tried our methodology by employing other ammonia
sources such as NH4F, (NH4)2SO4, (NH4)2CO3, and urea in
place of ammonium acetate under identical reaction conditions.
The yield of the reaction was decreased when these ammonia
sources were used (Table 1, entries 23–26). Noteworthy, when
maltose–DMU–NH4Cl was used in the absence of ammonium
acetate, the reaction can be proceeded, albeit affording the
desired product with diminished yield (55%, Table 1, entry 27).
In this case NH4Cl itself acts as an ammonia source in the for-
mation of quinazoline.
Importantly, the isolation and purification steps of this pro-
cedure are very simple. After completion of the reaction, water
was added. The components of the melt dissolved in water, and
products precipitated amorphously. The solid was isolated by
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Table 2 Synthesis of quinazoline derivatives in maltose–DMU–NH4Cl melta
m.p. (°C)
Found
Entry
X
R1
R2
Product
Time (min)
Yieldb (%)
Reported
18536
1
2
3
4
5
6
7
8
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
2-ClC6H4
2-ClC6H4
Me
Me
Me
C6H5
4a
4b
4c
4d
4e
4f
4g
4h
4i
4j
4k
4l
4m
4n
4o
4p
4q
4r
4s
4t
4u
4v
4w
4x
4y
4z
4aa
4ab
4ac
4ad
4ae
4af
4ag
4ah
4ai
4aj
4ak
4al
4am
4an
4ao
4ap
4aq
4ar
4as
180
170
150
90
86
88
91
93
88
89
90
88
90
86
84
87
91
81
91
91
93
86
87
91
89
91
87
90
88
90
85
86
83
85
85
88
93
88
90
86
82
79
80
82
90
86
86
89
88
185–186
216–218
208–210
180–181
213–214
174–175
172–174
95–96
187–188
186–187
163–164
177–179
194–195
126–127
220–223
160–161
161–162
172–173
190–192
225–226
108–109
46–47
120–121
165–166
155–156
185–186
115–117
172–174
98–99
140–143
159–161
182–183
194–195
152–153
124–125
143–144
146–147
204–206
215–217
198–199
178–179
195–196
87–88
4-CH3C6H5
4-OCH3C6H5
3,4-(OMe)2C6H3
2-OHC6H4
3-FC6H4
210–21527d
150
180
180
180
180
200
240
220
210
270
200
200
140
200
200
170
180
160
200
180
200
150
200
200
250
250
190
180
150
200
175
200
200
250
250
200
240
300
180
170
200
214–21537
17336
4-FC6H4
175–18027d
2-ClC6H4
3-ClC6H4
4-ClC6H4
2,4-Cl2C6H3
3-BrC6H4
4-BrC6H4
2-NO2C6H4
4-NO2C6H4
3-CF3C6H4
4-CF3C6H4
3-Pyridyl
4-Pyridyl
2-Thienyl
CH3CH2
CH3(CH2)7
C6H5
4-CH3C6H5
4-OCH3C6H5
4-OHC6H4
3-ClC6H4
4-ClC6H4
3-BrC6H3
4-BrC6H4
2-NO2C6H4
3-NO2C6H4
4-NO2C6H4
3-CF3C6H4
4-CF3C6H4
3-Pyridyl
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
185–18727d
16236
17836
12836
222–22437
16039
17336
19238
220–22337
11038
118–12027d
167–17027d
159–16227d
116–11838
193–19627d
9737
140–14527d
181–18338
19537
126–12927d
14236
2-Thienyl
3-FC6H4
14536
NO2
NO2
NO2
Cl
Cl
H
3-ClC6H4
3-CF3C6H4
3-CF3C6H4
2-Thienyl
3-ClC6H4
3-NO2C6H4
3-Pyridyl
H
H
138–139
104–105
105–10610
a Reaction conditions: 2-aminoaryl ketone (1 mmol), aldehyde (1 mmol), ammonium acetate (1 mmol) in maltose–DMU–NH4Cl melt (1.5 g) at
90 °C. b Isolated yield.
filtration, and pure product was obtained by crystallization from
ethanol. Alternatively, after completion of the reaction, the reac-
tion mixture was cooled to room temperature, the product was
extracted with ethyl acetate. The melt mixture was dried under
vacuum and was directly reused for the next round without
further purification. The melt mixture maintained high efficiency
even after being reused three times. The product 4ag was
obtained in 92%, 90%, and 89% yields after successive cycles.
after the reaction did not show any significant change, which
proved its stability under the reaction conditions.
Moreover, this simple procedure allowed easy scale-up of the
reaction, and as shown in Table 1, 90% yield was obtained in the
50 mmol scale reaction (Table 1, entry 28), indicating the prac-
ticability of our protocol.
To evaluate the substrate scope and limitations of this method-
ology, we extended our studies with a wide range of substrate
combinations. As shown in Table 2, this three-component
1
Furthermore, the H and 13C NMR spectra of the reaction media
1504 | Green Chem., 2012, 14, 1502–1506
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much easier than that of ketimine (II). Therefore, it is evidently
reasonable that the first mechanism is the right way to go.
Conclusion
In conclusion, we have developed a general, highly efficient, cat-
alyst-free, step-economic, and eco-friendly method for the syn-
thesis of quinazoline derivatives via the one-pot three-
component coupling reaction of 2-aminoaryl ketones, aldehydes,
and ammonium acetate under aerobic oxidation conditions using
low melting mixtures of maltose–dimethylurea (DMU)–NH4Cl
as a novel and green reaction medium. The simple work-up,
mild reaction condition and high yields make this new strategy
attractive for the preparation of a wide variety of biologically
relevant quinazolines.
Scheme 2 A proposed mechanism for the synthesis of product 4k.
reaction was performed well for most of the substrates. Both aro-
matic aldehydes and aliphatic aldehydes, were applicable in this
system. It was found that there was no remarkable electron and
position effects from the aromatic aldehydes for this reaction, as
evidenced by benzaldehydes with either an o-, m- or p-Cl substi-
tuent (Table 2, entries 8–10), which resulted in the correspond-
ing products (86–90%). Both 4-methoxybenzaldehyde (Table 2,
entry 3) and 4-nitrobenzaldehyde (Table 2, entry 15) were suit-
able substrates in this reaction. Of particular note, acid-sensitive
aldehydes such as thiophene-2-carbaldehyde and pyridin-2-alde-
hyde also worked well for this reaction. The reaction was well
tolerated with many other functional groups such as nitro,
halides, hydroxy, methoxy, and trifluoromethyl group on the sub-
strates. Nevertheless, a limitation was found in the reaction of
anthracene-9-carbaldehyde, which is less reactive in this system
and only a trace amount of desired product was detected. This
may indicate that the steric effect is serious enough to prevent
the reaction from taking place.
Experimental
General
Melting points were determined by using an X-4 melting point
apparatus. IR spectra were recorded on a Shimadzu FTIR-8900
1
spectrometer using KBr plates. The H NMR (500 MHz) and
13C NMR (125 MHz) spectra were recorded on a Bruker
DRX-500 spectrometer using CDCl3 as solvent and TMS as
internal standard. Elemental analyses were carried out on a Vario
EL III CHNOS elemental analyzer. Commercially available
reagents were used without further purification.
General procedure for the synthesis of quinazoline derivatives
To a round-bottomed flask containing 1.5 g of maltose–DMU–
NH4Cl (50 : 40 : 10), was added 2-aminoaryl ketone (1.0 mmol),
aldehyde (1.0 mmol) and ammonium acetate (1.0 mmol). The
mixture was heated at 90 °C under stirring, while air was
bubbled into the reaction. The progress of reaction was moni-
tored by TLC. After completion of the reaction, the mixture was
cooled to room temperature. Water was added, the precipitated
solid was collected by filtration and washed with water. This was
further purified by crystallisation from ethanol or by short
column chromatography on silica gel using ethyl acetate–
petroleum ether as the eluant.
Different substituents on the ketone moiety were also exam-
ined. It was found that the performance of this three-component
reaction strongly depends on the electronic property of the sub-
stituents on the aniline ring of 2-aminobenzophenone. In
general, electron-withdrawing groups worked well, affording
good-to-excellent yields in all cases. Unexpectedly, when 2-ami-
nobenzophenone with an electron-donating group, such as 2-
amino-5-methylbenzophenone, was used as the substrate, the
corresponding product failed to generate, even after prolonging
reaction time. Expediently, when 2-amino-benzophenone was
replaced by 1-(2-aminophenyl)ethanone, the reaction also led to
the formation of the desired quinazolines in high yields (Table 2,
entries 43–45).
Acknowledgements
Although the detailed mechanism for this three-component
reaction has not been established, according to the suggestions
from Sarma and Prajapati,35 product 4k could be formed via two
possible pathways (Scheme 2). To elucidate the reaction mechan-
ism, the reaction of (2-amino-5-chlorophenyl)(phenyl)metha-
none with 2,4-dichlorobenzaldehyde and ammonium acetate was
quenched at 40 min. It was found that 6-chloro-2-(2,4-dichloro-
phenyl)-4-phenyl-1,2-dihydroquinazoline (intermediate IV) was
formed. Furthermore, only a trace amount of product 4k was
obtained in the absence of air or under a nitrogen atmosphere.
This result demonstrated that air is necessary in the process for
the preparation of quinazoline derivatives. We think that the aro-
matisation of dihydroquinazoline is the rate determining step for
this three-component reaction. The formation of aldimine (I) is
We gratefully acknowledge the National Natural Science Foun-
dation of China (21072042 and 20872025) and Nature Science
Foundation of Hebei Province (B2011205031) for financial
support.
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