Synthesis of quinazolin-4(1 H)-ones via amination and annulation of amidines and benzamides

Article abstract of DOI:10.1039/c9ob00020h

Quinazolinones have broad applications in the biological, pharmaceutical and material fields. Studies on the synthesis of these compounds are therefore widely conducted. Herein, a novel and highly efficient copper-mediated tandem C(sp²)-H amination and annulation of benzamides and amidines for the synthesis of quinazolin-4(1H)-ones is proposed. This synthetic route can be useful for the construction of quinazolin-4(1H)-one frameworks.

Full text of DOI:10.1039/c9ob00020h

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Takeharu Haino et al.
Solvent-induced emission of organogels based on tris(phenylisoxazolyl)
benzene
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DOI: 10.1039/C9OB00020H
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Synthesis of Quinazolin-4(1H)-ones via Amination and Annulation
of Amidines and Benzamides
Fangpeng Hu,a Xinfeng Cui,a Zihui Ban,a Guoqiang Lu,a Nan Luoa and Guosheng Huang*a
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
www.rsc.org/
Quinazolinones have board applications in biological,
pharmaceutical and material fields. Studies on the synthesis of
these compounds are therefore widely conducted. Herein, a novel
and highly efficient copper-mediated tandem C(sp2)-H amination
and annulation of benzamides and amidines for the synthesis of
quinazolin-4(1H)-ones is proposed. This synthetic route can be
useful for the construction of quinazolin-4(1H)-ones frameworks.
Previous works
(a) Fu
O
O
N
H2N
COOH
NH2
Cu cat.
metal-free
Pd(OAc)2
NH
+
Br
(b) Li
O
O
H
R2
Ar
R2
H
H
N
N
+
R1
R1
H
Ar
Quinazolinone skeletons are widely prevalent in natural
products, biologically active compounds and other materials.1
Owing to their ubiquitous nature and their importance as a
pharmacophore in modern medicinal chemistry,2 these
N
NH2
(c) AIper
R
O
R1
I
R
R1
R2
N
N
+
heterocycles have been widely synthesized by various
R2
Cl
NH2
N
14b-c, 15c
methods.3,
Among these methods, the acid/base-
Our work
mediated condensation reaction of carboxylic acid derivatives
with 2-aminobenzoic acid and its derivatives, and the cascade
condensation reaction of aldehydes with o-aminobenzamides,
which is followed by oxidation of aminal intermediate, have
attracted considerable attention because of their extensive
potential applications.4 However, these methods suffer from
some unignorable drawbacks. For example, they have limited
scope due to their multi-step reactions, harsh reaction
conditions, and unsatisfactory yields, in addition to other
ineluctable disadvantages.5 As a result, development of an
efficient, environmentally benign catalyst system for the
preparation of heterocycle quinazolines is highly desirable.
Over the last few decades, several alternative strategies
have been established to synthesize quinazolinones.
For example, in 2014, Fu employed a copper-catalyzed domino
method to synthesize quinazolin-4(3H)-ones using readily
available α-amino acids as the substrates (Scheme 1, path a).6
Wang also investigated a novel cascade method, α-MnO2-
catalyzed oxidative cyclization, using anthranilamides or
O
N
O
H
N
NH
Cu(OAc)2
N
H
+
N
H
N
O
Scheme 1. Comparison of synthetic route to quinazolinones in previous works
(paths a-c) and that in our work.
aminobenzylamines and alcohols as the starting materials.7 Li
and colleagues also developed a novel metal-free oxidative
synthesis of quinazolinones via dual amination of sp3 C–H
bonds (Scheme 1, path b).8 Alper found that quinazolinones
can be prepared by palladium-catalyzed cyclocarbonylation of
o-iodoanilines, imidoyl chlorides and carbon monoxide
(Scheme 1, path c).9 Recently, Liu described a new strategy, a
copper-mediated tandem reaction of benzamides with 2-
aminopyridines, to produce 11H-pyrido[2,1-b]quinazolin-11-
ones.10
In synthetic organic chemistry transition-metal-catalyzed C-
N/C-H bonds formation have emerged as a powerful method
for the synthesis of nitrogen-containing compounds.11-12 In the
past few decades, rhodium-, palladium- and ruthenium-based
catalysts have been used mainly in the construction of C-C or
C-Het (Het = heteroatom) bond.13-14 Due to its low cost, high
reactivity and environmental friendliness, copper has recently
received tremendous attention.15-16 Meanwhile, the
aState Key Laboratory of Applied Organic Chemistry, Key Laboratory of
Nonferrous Metal Chemistry and Resources Utilization of Gansu Province,
Department of Chemistry, Lanzhou University, Lanzhou 730000, China. E-mail:
hgs@lzu.edu.cn
†Electronic Supplementary Information (ESI) available: [details of any
supplementary information available should be included here]. See
DOI: 10.1039/x0xx00000x
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Table 1. Screening of reaction conditions.a)
Table 2. Substrate scope of benzamides.a)
View Article Online
DOI: 10.1039/C9OB00020H
O
N
O
O
N
N
O
H
R
NH
NH
conditions
Cu(OAc)2 (1.0 equiv), DMSO
N
N
N
H
R
H
+
N
+
N
90oC, air, 12h
H
H
H
N
O
N
O
1
1a
2a
3
2a
3a
O
N
O
N
N
O
N
O
Entry
1
Cu salt
Oxidant
-
Solvent
T [℃]
50
Yield [b] [％]
N
N
N
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2·H2O
Cu(OTf)2
CuI
DMSO
DMSO
DMSO
DMSO
DMF
44
MeO
N
2
3
-
70
110
90
90
90
90
90
90
90
90
90
90
90
90
90
90
90
71
72
-
3a, 75%
O
3c, 55%
3d, 27%
3b, 66%
O
4
-
75
Br
O
N
O
N
N
5
-
Trace
19
N
N
N
6
-
1,4-Dioxane
CH3CN
Toluene
DCE
Cl
N
F
N
Br
7
-
26
8
-
20
3e, 80%
3f, 74%
3g, 45%
3h, 71%
9
-
9
O
N
N
Cl
O
O
N
N
O
N
N
10
11
12
13
14
15
16
17
18
-
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
69
F3C
N
F3C
-
47
N
-
-
60
CuBr
Trace
0
3i, 37%
3j, 55%
3k, 57%
3l, 0%
-
-
O
N
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
O2
25
N
K2S2O8
BQ
BPO
23
NC
Trace
60
3m, 58%
a)Reaction conditions: amide 1a (0.1 mmol), 2a (0.16 mmol), Cu salt (0.1
mmol), solvent (1.0 mL), 90 ℃ under air for 12 h. b) Isolation yield.
3a
a)Reaction conditions: amide 1 (0.1 mmol), 2a (0.16 mmol), Cu salt (0.1
mmol), solvent (1.0 mL), 90 ℃ under air for 12 h.
precedents in which successive C-H activation/removal of
directing group have been reported.17, 10 Herein, we developed
a
copper-mediated tandem-annulation reaction for the
Using the optimal reaction conditions (Table 1, entry 4), we
subsequently investigated a wide range of amides substrates,
and the results are summarized in Table 2. The amides bearing
electron-donating groups (-Me, -OMe) and electron-
withdrawing groups (-F, -Cl, -Br, -CF3 and -CN) were moderately
compatible, thereby could afford the desired products with
moderate to good yield (3b–3k, 3m). For example, the
electron-rich methyl-substituted amides could afford the
desired quinazolinone derivatives 3b and 3c with 66% and 55%
yields, respectively. Additionally, the methoxy-substituted
amide gave the corresponding product 3d with 27% yield. On
the other hand, the electron-deficient amides bearing halogen
and trifluoromethyl groups resulted in the desired products in
moderate to good yields (3e-3k; 37-80% yield). Interestingly, o-
amides bearing bromide or chloride atom gave the
corresponding products 3g and 3i with 45% and 37% yields;
this could be attributed to steric hindrance effect. However,
the desired product 3l was not observed when 1-
naphthylamide was used as a substrate under the optimal
conditions.
synthesis of quinazolin-4(1H)-ones from amidines and
benzamides.
In
our
initial
studies,
1a
N-(2-(4,5-dihydrooxazol-2-
(0.1 mmol) and N-
yl)phenyl)benzamide
phenylbenzimidamide 2a (0.16 mmol) were chosen as model
substrates in the presence of Cu(OAc)2 (0.1 mmol) in DMSO
(1.0 mL) at 50 C for 12 h. To our delight, the desired product,
o
1,2-diphenylquinazolin-4(1H)-one 3a, was obtained with 44%
yield (Table 1, entry 1). Encouragingly, the yield was improved
to 75% when the temperature was increased to 90 °C (Table 1,
entry 4). We found that, DMSO was the most efficient solvent
among all solvents that were screened, Other non-polar
solvents, (such as DCE and toluene), and polar solvents, (such
as DMF, 1,4-dioxane and CH3CN), were poor solvents (Table 1,
entries 4-9). Furthermore, several copper salts were screened,
and Cu(OAc)2 was found to give the highest product yield
(entries 9-13). The screening of oxidants showed that they only
slightly improved the yields (entries 15-18). It is worth noting
that, in the absence of copper salts, the reaction could not
proceed. This indicates that the copper catalyst is necessary
for the reaction (entry 14).
We further investigated the reactions of N-aryl ring (R1)
substituted amidines (3aa-3ai). As shown in Table 3, various
2 | J. Name., 2012, 00, 1-3
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O
Table 3. Substrate scope of 2-aminopyridines.a)
O
View Article Online
N
DOI: 10.1039/C9OB00020H
H
O
N
NH
O
N
N
O
standard reaction
Tempo (3.0 equiv.)
N
N
NH
+
H
+
N
O
N
3
H
H
NH
N
O
Cu(OAc)2 (1.0 equiv), DMSO
N
N
H
+
N
R1
90oC, air, 12h
1a
H
2a
3a 70%
S
R2
H
N
O
Detected by HRMS-ESI
R2
R1
1a
2
Cl
O
Cl
O
NH
N
O
N
O
N
O
O
N
N
NH
standard reaction
N
H
+
N
N
N
N
H
Cl
N
O
Cl
5, not observed
N
2a
4
Scheme 2. Reactions carried out in control experiments.
OMe
3aa, 66%
3ab, 70%
3ac, 72%
3ad, 65%
and 2-naphthyl amidines gave products 3ak (70% yield) and
3aj (67% yield) with remarkable yields, the desired product 3al
was not obtained. The desired products (3ba-3bf) were
obtained in moderate to excellent yields (57-80%) when
another aryl ring (R2) was added.
O
N
N
O
N
N
O
N
O
N
N
N
Cl
Effects of other directing groups were also examined. The
monodentate coordinated benzamides (Table 4, C-E) failed to
produce the corresponding product 3a, while other
representative bidentate coordinated benzamides (Table 4, A
and B) gave the corresponding product 3a in 41% and 10%
yields, respectively.
F
Cl
3af, 60%
3ae, 64%
3ag, 65%
3ah, 63%
O
N
N
O
N
O
N
N
O
N
N
N
N
Cl
To gain insights into the reaction mechanism, a series of
control experiments were carried out, as shown in Scheme 2.
First, a stoichiometric amount of the radical inhibitor 2,2,6,6-
tetramethylpiperidine-N-oxyl (TEMPO) was used under the
optimal reaction conditions, and the desired product 3a was
obtained with 70% yield, which is a slight decrease compared
with the yield obtained from the optimal reaction conditions.
This indicates that a free radical pathway is not involved in the
3ak, 70%
3al, 0%
3ai, 62%
3aj, 67%
O
N
N
O
N
N
O
N
N
O
N
N
F
CF3
3bb, 71%
3bc, 58%
3bd, 65%
3ba, 79%
reaction. Fortunately, the potential intermediate
S was
O
N
N
O
N
N
detected by HRMS-ESI (m/z = 461) (see the Supporting
Information). However, the ortho-blocked amide 4 failed to
give the intermediate 5. These control experiments prompted
us to interpret that the tandem reaction is likely initiated with
C(sp2)-H amination of benzamides and amidines. Amide
carbonyl group then induce intramolecular nucleophilic
substitution, which in turn gives quinazolin-4(1H)-ones.
Based on these results and the literature data,15c, 10, 18 we
propose a plausible mechanism for the tandem reaction of N-
(2-(4,5-dihydrooxazol-2-yl)phenyl)benzamides and amidines in
the synthesis of 1,2-diphenylquinazolin-4(1H)-one (Scheme 3).
Br
Br
3be, 57%
3bf, 80%
a)Reaction conditions: amide 1a (0.1 mmol), 2 (0.16 mmol), Cu salt (0.1
mmol), solvent (1.0 mL), 90 ℃ under air for 12 h.
electron-donating
substituted N-aryl ring gave the 1,2-diphenylquinazolin-4(1H)-
and
electron-withdrawing
groups
ones in moderate to good yields (60-72%). While 1-naphthyl
O
O
O
Cu(OAc)2
Cu(OAc)
Cu(OAc)2
-HOAc
N
-HOAc
N
N
1a
Table 4. Other directing groups
II
III
II
Cu
Cu
Cu
N
O
N
O
H
N
O
AcO
AcO
O
O
O
O
B
C
A
OPiv
N
O
O
N
N
N
H
H
H
N
N
N
N
III
2a
H
Cu
N
N
O
N
O
N
-HOAc
-Q-NH2
C, 0%
NH
A, 41%
O
N
B, 10%
O
CuI
HN
3a
D
S
OMe
N
H
N
H
Scheme 3. Plausible mechanistic pathway.
D, 0%
E, 0%
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C-H cupration to give the species B. Cu(OAc)2-promoted
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5
undergoes
a reductive elimination to produce the key
intermediate S (as detected by HRMS-ESI). Finally, the target
product 3a is produced by intramolecular nucleophilic
substitution of S.
6
7
We designed and developed a convenient, operationally
simple, and highly efficient protocol for the synthesis of
quinazolinone derivatives. Notably, one feature of this new
protocol is that it can used novel starting material N-(2-(4,5-
dihydrooxazol-2-yl)phenyl)benzamides as bidentate-directing
groups. The reaction uses copper as the catalyst, thus the use
of expensive noble metals can be avoided. Unfortunately, we
cannot find the possible directing group after the reaction.
Currently, the application of this protocol in the synthesis of
other products is under investigation in our laboratory.
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Conflicts of interest
There are no conflicts to declare.
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