Hydrogen peroxide-mediated synthesis of 2,4-substituted quinazolines: Via one-pot three-component reactions under metal-free conditions

Article abstract of DOI:10.1039/d0ra05040g

An efficient metal-free synthesis of 2,4-substituted quinazolines via a hydrogen peroxide-mediated one-pot three-component reaction of 2-aminoaryl ketones, aldehydes, and ammonium acetate has been developed. The transformation proceeded readily under mild conditions in the presence of commercially available hydrogen peroxide. The significant advantages of this approach are (1) the readily available atom-efficient and green hydrogen peroxide as oxidant; (2) no transition metal catalyst is required; (3) mild reaction conditions; and (4) wide substrate scope. To the best of our knowledge, utilizing hydrogen peroxide as an atom-efficient and green oxidant for the synthesis of 2,4-substituted quinazolines has not previously been reported in the literature. This method is complementary to previous protocols for the synthesis of 2,4-substituted quinazolines. This journal is

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PAPER
Hydrogen peroxide-mediated synthesis of 2,4-
substituted quinazolines via one-pot three-
component reactions under metal-free conditions†
Cite this: RSC Adv., 2020, 10, 29900
ab
ab
ab
Khang H. Trinh,
Tung T. Nguyen,
‡
Khang X. Nguyen,
‡
Phuc H. Pham,
ab
ab
ab
*
*
Anh N. Q. Phan
and Nam T. S. Phan
An efficient metal-free synthesis of 2,4-substituted quinazolines via a hydrogen peroxide-mediated one-
pot three-component reaction of 2-aminoaryl ketones, aldehydes, and ammonium acetate has been
developed. The transformation proceeded readily under mild conditions in the presence of commercially
available hydrogen peroxide. The significant advantages of this approach are (1) the readily available
atom-efficient and green hydrogen peroxide as oxidant; (2) no transition metal catalyst is required; (3)
mild reaction conditions; and (4) wide substrate scope. To the best of our knowledge, utilizing hydrogen
peroxide as an atom-efficient and green oxidant for the synthesis of 2,4-substituted quinazolines has not
previously been reported in the literature. This method is complementary to previous protocols for the
synthesis of 2,4-substituted quinazolines.
Received 8th June 2020
Accepted 3rd August 2020
DOI: 10.1039/d0ra05040g
rsc.li/rsc-advances
ammonium acetate.13 Saikia et al. achieved quinazolines by
a trimethylsilyltriuoromethane sulfonate-catalyzed activa-
tion of aliphatic and aromatic nitriles.14 Chen et al. prepared
quinazolines from DMSO-mediated transformation of
anilines, aromatic aldehydes, and ammonium iodide under
oxygen atmosphere.15
1. Introduction
Quinazolines and their derivatives are a privileged class of
nitrogen-containing heterocyclic compounds, normally
occurring in a variety of natural products and synthetic
chemicals with a wide spectrum of biological and medicinal
activities.1–4 Due to their pharmaceutical applications and
signicant biological value, a variety of methodologies have
been explored for the synthesis of these structures. Typical
approaches started from ortho-functionalized anilines and
derivatives, such as 2-carbonyl anilines,5 2-aminobenzyl-
amines,6 and 2-aminobenzonitriles.7 Recently, several new
strategies from diversied starting materials using transition
metal catalysts have been developed for the construction of
substituted quinazolines.8–11 Additionally, metal-free synthetic
pathways to these heterocyclic compounds have attracted
signicant interest. Zhang et al. previously achieved quinazo-
lines via a one-pot three-component reaction of 2-aminoaryl
ketones, aldehyde, and ammonium acetate in mixtures of
maltose-dimethylurea (DMU)–NH4Cl.12 Zhao et al. demon-
strated a KI-catalyzed three-component synthesis of quinazo-
lines utilizing 2-aminophenyl ketones, methylarenes, and
Hydrogen peroxide has been considered as an ideal oxidant
for liquid-phase green chemistry as it is non-toxic, environ-
mentally benign, and atom efficient, producing only water as
theoretical by-product.16–18 Additionally, utilizing hydrogen
peroxide as oxidant normally does not require temperatures
over 100 ꢀC for oxidation transformations.17 In organic
synthesis, low efficiency of hydrogen peroxide has limited its
applications, and organic peroxides are preferred in many
cases. There has been growing interest in employing hydrogen
peroxide as green oxidant in many synthetic strategies. Doherty
et al. successfully replaced strong oxidants by hydrogen
peroxide for sulfoxidation reactions.19 Devi et al. previously
employed hydrogen peroxide instead of organic peroxides for
the synthesis of N-(pyridin-2-yl)benzamides.20 Zhou et al.
described hydrogen peroxide-mediated transformations of
enamides to generate substituted a-acyloxyketones.21 Lindhorst
et al. conducted oxidations of aromatic hydrocarbons using
hydrogen peroxide as green oxidant.22 Yaremenko et al. con-
verted 1,5-diketones to ozonides in the presence of hydrogen
peroxide.23 Qiu et al. demonstrated an efficient oxidation of
methylene C–H in oxindoles or 2,3-dihydroquinolin-4-ones by
utilizing hydrogen peroxide.24 In this work, we would like to
report a metal-free synthesis of 2,4-substituted quinazolines via
hydrogen peroxide-mediated one-pot three-component reaction
of 2-aminoaryl ketones, aldehydes, and ammonium acetate
aFaculty of Chemical Engineering, Ho Chi Minh City University of Technology (HCMUT),
268 Ly Thuong Kiet, District 10, Ho Chi Minh City, Vietnam. E-mail: pnqanh@hcmut.
edu.vn; ptsnam@hcmut.edu.vn; Fax: +84 8 38637504; Tel: +84 8 38647256, ext. 5681
bVietnam National University Ho Chi Minh City, Linh Trung Ward, Thu Duc District,
Ho Chi Minh City, Vietnam
† Electronic supplementary information (ESI) available. See DOI:
10.1039/d0ra05040g
‡ These authors contributed equally to this work.
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Scheme 1 Synthesis of 2,4-substituted quinazolines via hydrogen peroxide-mediated one-pot three-component reactions.
(Scheme 1). High yields were achieved under mild reaction only 44% yield being recorded for the reaction performed at
conditions.
120 ꢀC. It should be noted that decreasing the reaction time
from 24 h to 6 h led to 90% yield of 3aa (entry 12). Indeed,
experimental results indicated that pyridine-3-carboxylic acid
was produced as by-product at high temperature or aer long
reaction time. Additionally, the reactant molar ratio exhibited
a noticeable inuence on the formation of 3aa (entries 7–17).
Utilizing excess amounts of 2a favored the transformation,
while signicantly lower yields were detected in the presence of
excess amounts of 1a.
2. Experimental
In
a representative experiment, a
mixture of 20-amino-
acetophenone (13.6 mg, 0.1 mmol), 3-pyridinecarboxaldehyde
(21.5 mg, 0.2 mmol), NH4OAc (23.2 mg, 0.3 mmol), and
diphenyl ether (17.1 mg, 0.1 mmol) as an internal standard in
dimethylsulfoxide (DMSO; 1 mL, 14 mmol) was added into
a 8 mL screw-cap vial. The reaction mixture was magnetically
stirred for 2 min to disperse entirely reactants in the liquid
phase, followed by the addition of hydrogen peroxide (H2O2;
30 wt% in H2O; 0.4 mmol, 41.2 mL). The resulting mixture was
With these results in hand, we subsequently investigated the
impact of solvent on the formation of 3aa. The reaction was
ꢀ
carried out at 60 C for 6 h, using 2 equivalents of 2a, 3 equiv-
alents of ammonium acetate, and 4 equivalents of hydrogen
peroxide, in different solvents including chlorobenzene, 1,2-
dichlorobenzene, dioxane, DMF, DMSO, NMP, and DMAc,
respectively (entries 18–23). It was noted that the solvent
exhibited a signicant impact on the reaction, and DMSO
emerged as the best option (entry 12). The transformation was
also controlled by the amount of the nitrogen source (entries
24–27). Using 1 equivalent of ammonium acetate afforded 44%
yield (entry 24), while 90% yield was obtained in the presence of
2 equivalents of ammonium acetate (entry 12). Nevertheless,
extending the amount of ammonium acetate resulted in lower
yields. Next, a series of oxidants were tested for the reaction,
including both organic and inorganic oxidants (entries 28–33).
The reaction conducted under air without any additional
oxidant afforded 55% yield (entry 29), and this value was
improved to 69% for the reaction carried out under molecular
oxygen (entry 30). Interestingly, utilizing the readily available
hydrogen peroxide afforded 90% yield of 3aa (entry 12). Organic
peroxides such as di-tert-butylperoxide or tert-butyl hydroper-
oxide in water exhibited lower efficiency than hydrogen
peroxide. Indeed, besides air and molecular oxygen, hydrogen
peroxide should be utilized as the most atom-efficient and
green oxidant. Furthermore, the transformation was controlled
by the amounts of hydrogen peroxide (entries 34–38), and
utilizing 4 equivalents offered best yield of 3aa (entry 12).
Based on these results, the scope was then extended to the
synthesis of many substituted quinazolines via the hydrogen
peroxide-mediated three-component reaction of 2-aminoaryl
ketones, aldehydes, and ammonium acetate (Table 2). The
reaction was carried out in DMSO at 60 ꢀC for 6 h, with 2
equivalents of the aldehyde, using 3 equivalents of ammonium
ꢀ
subsequently stirred at 60 C for 6 h. The reaction yield moni-
tored by withdrawing aliquots from the reaction mixture, and
quenched with brine. The organic components were conse-
quently extracted into ethyl acetate (2 mL), dried over anhy-
drous Na2SO4, and analyzed by GC with reference to diphenyl
ether. To isolate the desired product, aer disappearance of the
reactant (monitored by TLC), the mixture was slowly cooled to
room temperature and diluted with ethyl acetate (20 mL),
washed with saturated NaHCO3 solution (3 ꢁ 5 mL), dried over
anhydrous Na2SO4, and concentrated under vacuum. The crude
product was puried by column chromatography on silica gel
with hexane/ethyl acetate solvent system to give pure product.
The product structure was conrmed by 1H NMR, and 13C NMR.
3. Results and discussion
Initially, the three-component reaction between 20-amino-
acetophenone (1a), 3-pyridinecarboxaldehyde (2a), and ammo-
nium acetate to produce 4-methyl-2-(pyridin-3-yl)quinazoline
(3aa) was investigated (Table 1). Preliminary studies indicated
that an oxidant was required for this transformation. Reaction
conditions were screened to maximize the yield of 3aa, con-
cerning temperature, reactant molar ratio, solvent, ammonium
acetate amount, oxidant, and oxidant amount. The reaction was
conducted in DMSO for 24 h, using 2 equivalents of 2a, 3
equivalents of ammonium acetate, and 4 equivalents of
hydrogen peroxide, at temperature ranging from ambient to
ꢀ
120 C (entries 1–6). Best result was obtained for the reaction
conducted at 60 ꢀC with 84% yield of 3aa being detected (entry
3). Increasing the temperature resulted in lower yields, with
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Table 1 Screening reaction conditionsa
Temperature
(ꢀC)
1a : 2a
(mol : mol)
NH4OAc amount
(equiv.)
Entry
Solvent
Oxidant
Oxidant amount (equiv.)
Yieldb (%)
1
2
3
4
5
6
7
8
RTc
40c
60c
80c
100c
120c
60
60
60
60
60
60
60
60
60
60
60
60
60
60
60
60
60
60
60
60
60
60
60
60
60
60
60
60
60
60
60
60
1 : 2
1 : 2
1 : 2
1 : 2
1 : 2
1 : 2
1 : 1
1 : 1.2
1 : 1.4
1 : 1.6
1 : 1.8
1 : 2
1 : 3
1 : 4
2 : 1
3 : 1
4 : 1
1 : 2
1 : 2
1 : 2
1 : 2
1 : 2
1 : 2
1 : 2
1 : 2
1 : 2
1 : 2
1 : 2
1 : 2
1 : 2
1 : 2
1 : 2
1 : 2
1 : 2
1 : 2
1 : 2
1 : 2
1 : 2
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DCB
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
1
2
4
5
3
3
3
3
3
3
3
3
3
3
3
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
TEMPO
Air
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
—
—
4
4
4
0
1
2
3
5
42
45
84
83
62
44
51
58
71
78
81
90
59
31
54
59
60
17
28
42
62
71
72
44
73
84
80
22
55
69
61
67
83
55
72
75
85
80
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
PhCl
Dioxane
DMF
DMAc
NMP
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
O2
DTBP
K2S2O8
aqTBHP
H2O2
H2O2
H2O2
H2O2
H2O2
a
Reaction conditions: 20-aminoacetophenone (0.1 mmol); solvent (1 mL); under air; 6 h. DMSO: dimethyl sulfoxide; DMF: N,N-dimethylformamide;
DMAc: N,N-dimethylacetamide; DCB: 1,2-dichlorobenzene; NMP: N-methyl-2-pyrrolidone; DTBP: di-tert-butylperoxide; aqTBHP: tert-butyl
hydroperoxide in water; dcTBHP: tert-butyl hydroperoxide in decane. b GC yield. c The reaction was carried out in 24 h.
acetate, and 4 equivalents of hydrogen peroxide. Products were with aliphatic aldehydes was also feasible, yielding 2,4-dia-
consequently puried by column chromatography. In the rst lkylsubstituted quinazolines 3ae, 3ag, 3ah in good yields
series, several aromatic aldehydes were utilized for the reaction (entries 5–7). Next, 1-(6-aminobenzo[d][1,3]dioxol-5-yl)ethan-1-
with 20-aminoacetophenones and ammonium acetate. Under one was employed for the reaction with different aldehydes,
these conditions, 3aa, 3ab, 3ac, and 3ad were achieved in 88%, producing 3ba, 3bb, 3bc, and 3bd in 74%, 78%, 75%, and 72%
89%, 75%, and 74% yields, respectively (entries 1–4). Coupling yields, respectively (entries 8–11). Moving to the transformation
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Table 2 Synthesis of 2,4-substituted quinazolines via one-pot three-component reaction of 2-aminoaryl ketones, aldehydes, and ammonium
acetatea
Entry
Reactant 1
Reactant 2
Product
Yieldb (%)
1
88
2
89
3
4
75
74
5
6
70
75
7
85
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Table 2 (Contd.)
Entry
Reactant 1
Reactant 2
Product
Yieldb (%)
8
74
9
78
10
75
11
72
12
72
13
75
14
70
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Table 2 (Contd.)
Entry
Reactant 1
Reactant 2
Product
Yieldb (%)
15
69
16
84
17
85
18
78
19
68
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Table 2 (Contd.)
Entry
Reactant 1
Reactant 2
Product
Yieldb (%)
20
69
21
70
22
68
23
61
a
Reaction conditions: reactant 1 (0.1 mmol); reactant 2 (0.2 mmol); NH4OAc (0.3 mmol); H2O2 (0.4 mmol); DMSO (1 mL); 60 ꢀC; under air; 6 h.
Isolated yields.
b
of 1-(2-amino-4,5-dimethoxyphenyl)ethan-1-one with several 18). Similarly, 2-aminobenzophenone derivatives containing
aldehydes, 3ca, 3cb, 3cc, and 3cd were generated in 72%, 70%, different substituents were employed for the reaction,
75%, and 69% yields, respectively (entries 12–15). In the second producing corresponding products in reasonable yields (3ea,
series, many 2-aminobenzophenones were used for the three- 3fa, 3ga, and 3ha) (entries 19–23).
component reaction with various aldehydes. It was found that
To gain insight into the possible mechanism on the formation
2-aminobenzophenones were also reactive towards the trans- of the quinazoline products, several control experiments were
formation. Under standard conditions, 3db, 3dc, and 3dd were conducted. The reaction between 1a and 2a was performed in the
obtained in 85%, 78%, and 68% yields, respectively (entries 16– absence of hydrogen peroxide. Except for the generation of desired
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Scheme 2 Control experiments.
Scheme 3 Proposed reaction pathway.
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product 3aa in 55% yield, the dihydroquinazoline intermediate
3aa0 was observed by GC-MS analysis in trace amount (Scheme 2a).
In another control experiment, hydrogen peroxide was subse-
quently added into the reaction mixture depicted in Scheme 2a
and the resulting solution was stirred for a further 3 h (Scheme
2b). As expected, 90% yield of target product 3aa was obtained in
the presence of 3 equivalents of hydrogen peroxide. It should be
noted that 64% and 78% yields of 3aa was detected when 1 and 2
equivalents of hydrogen peroxide were utilized, respectively. These
observations suggested that compound 3aa0 was the reaction
intermediate. The similar result was achieved when the reaction
between 1a and 2a was conducted under argon atmosphere
(Scheme 2c). These observations conrmed the essential role of
active oxygen species for the transformation.
Based on experimental observations and previous
reports,6,12,15 the proposed pathway for the formation of quina-
zoline derivatives was shown in Scheme 3. Firstly, ammonium
acetate was decomposed to NH3 and AcOH by heating.
Condensation between 20-aminoacetophenone 1a with NH3
occurred to give imine A. Subsequent condensation between the
amino moiety of imine A with aldehyde 2a, followed by nucle-
ophilic cyclization, generated the dihydroquinazoline interme-
diate 3aa0. The key intermediate 3aa0 can be rapidly oxidized to
the nal product 3aa in the presence of hydrogen peroxide and
DMSO.
Acknowledgements
We would like to thank the Viet Nam National Foundation for
Science and Technology Development (NAFOSTED) for nancial
support under Project code 104.05-2018.330 (PI: Anh N. Q. Phan).
Ms Thu T. H. Nguyen is acknowledged for her help in taking
samples.
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In summary, we have developed an efficient metal-free
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transformation proceeded readily under mild conditions in the
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formation of 2,4-substituted quinazolines. Reaction conditions
were compatible with numerous functionalities. Aromatic,
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quinazolines in good yields. The signicant advantages of this
approach are the (1) easily available atom-efficient and green
hydrogen peroxide as oxidant; (2) no transition metal catalyst is
required; (3) mild reaction conditions; and (4) wide substrate
scope. To the best of our knowledge, utilizing hydrogen
peroxide as atom-efficient and green oxidant for the synthesis of
2,4-substituted quinazolines was not previously reported in the
literature. This strategy provides an efficient and environmen-
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There are no conicts to declare.
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