Base-promoted Lewis acid catalyzed synthesis of quinazoline derivatives

Article abstract of DOI:10.1039/d0ob00225a

A one-pot protocol has been developed for the synthesis of quinazolinones from amide-oxazolines with TsCl via a cyclic 1,3-azaoxonium intermediate and 6π electron cyclization in the presence of a Lewis acid and base. The process is operationally simple and has a broad substrate scope. This method provides a unique strategy for the construction of quinazolinones.

Full text of DOI:10.1039/d0ob00225a

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DOI: 10.1039/D0OB00225A
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Base-promoted Lewis acid catalyzed synthesis of quinazoline
derivatives
Fang-Peng Hu, Xin-Feng Cui, Guo-Qiang Lu and Guo-Sheng Huang*
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
A one-pot protocol has been developed for the synthesis of
quinazolinones from amide-oxazolines with TsCl via a cyclic 1,3-
azaoxonium intermediate and 6π electron cyclization in the
presence of a Lewis acid and base. The process is operationally
simple and has a broad substrate scope. This method provides a
unique strategy for the construction of quinazolinones.
Previous work
O
O
O
O
OH
NH2
NH2
NH2
a-MnO2
NH
N
Ph
+
N2
+
Ph
N
TBHP
NH2
TFA
(a) Wang
(b) Cui
O
N
O
Cl
Lewis acid
Base
This work
Ph
N
+
TsCl
H
Ph
N
O
The synthesis of nitrogen-containing heterocycles has attracted
significant attention over the years because nitrogen- Scheme 1 Comparison of previously published synthetic routes to quinazolinones
(paths a–b) and the route in this work.
containing heterocycles are ubiquitous components of a variety
of biologically active compounds.1 Among these,
2-aminobenzamides14 with carboxylic acid derivatives.
quinazolinones are common structural motifs found in a large
However, these traditional methods have some limitations and
number of natural products and play a significant role in the
restrictions, including harsh reaction conditions, unsatisfactory
synthesis of pharmaceutical compounds. For example, luotonin
A from Peganum nigellastrum has powerful anti-tumor
yields, multi-step reactions, and the use of stoichiometric or
large excess amounts of toxic oxidants. More research is
properties in the murine leukemia P-388 cell line and stabilizes
required to overcome these limitations and achieve cost-
the human topoisomerase I-DNA covalent binary complex.2
Febrifugine, isolated from the Asian plant Dichroa febrifuga, an
effective, environmentally-friendly and easy to handle synthetic
approaches.
ingredient in a traditional Chinese herbal remedy, is effective
In recent years, several new synthetic approaches have been
against malaria.3 Chaetominine, an alkaloidal metabolite with a
new framework, isolated from Adenophora axilliflora, is more
cytotoxic than 5-fluorouracil against the human leukemia K562
established for the synthesis of quinazolinones. In 2015, Wang
et al. developed a highly active and selective method that
employed a-MnO2 as a catalyst and tert-butyl hydroperoxide
and colon cancer SW1116 cell lines.4 In addition, quinazolinone-
(TBHP) as the oxidant to synthesize quinazolinones and
containing compounds have a broad range of therapeutic
quinazolines using anthranilamides or aminobenzylamines as
activities, including anticonvulsant,5 antiviral,6 antidiabetic,7
the substrates (Scheme 1, path a).15 In 2014, Cui and co-workers
antibacterial,8
anti-inflammatory,9
and
anaesthetic10
reported a significant protocol for the synthesis of 4(3H)-
quinazolinones via the selective cleavage of the triple bond of
ketoalkynes under oxidant-, metal-, and ligand-free conditions
(Scheme 1, path b).16 Alternatively, an interesting palladium-
catalyzed cyclocarbonylation of o-iodoanilines with imidoyl
chlorides to produce quinazolin-4(3H)-ones has been described
by Kapdi and co-workers.17 In another report, Tripathi et al. have
developed a novel and efficient Cu(I)-catalyzed ligand- and
base-free multi-pathway domino method for synthesizing 2-
substituted quinazolinones.18 We have just published a copper-
mediated tandem-annulation reaction for the synthesis of
quinazolin-4(1H)-ones from aryl amide-oxazolines and
benzamides.19
properties. Some quinazolinones are undergoing clinical trials
as cancer treatments and are promising candidates for new
facile and practical synthesis approaches.11
In view of their remarkable therapeutic activity, great efforts
have been devoted toward developing efficient and convenient
strategies for the construction of the quinazolinone skeleton.
Many studies have reported the catalytic synthesis of
quinazolinones from aldehydes and amides using transition
metal catalysts like Fe, Pd, Ru, and Ir.12 Commonly,
quinazolinones have been prepared via the amidation of 2-
aminobenzoic acid and its derivatives13 or the condensation of
Substituted amide-oxazolines are present in many
pharmaceuticals, functional materials, and ligands,20 and have
been widely used in the functionalization of C-H bonds to form
State 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
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Table 1 Screening of reaction conditionsa
Table 2 Benzamide substrate scopea
R2
View Article Online
DOI: 10.1039/D0OB00225A
O
N
O
O
O
Cl
DMAP (0.2 equiv)
N
condition
Cl
N
N
+
TsCl
Cu(OAc)2 H2O (0.2 equiv)
R2
R
N
H
TsCl
+
H
N
O
DCE, 120oC, 10h
N
R
N
O
1a
2
3a
Entry
Base
Solvent
Lewis acid
Yield(%)b
T(℃)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
K2CO3
Na2CO3
DMAP
DABCO
-
DMAP
DMAP
DMAP
DMAP
DMAP
DMAP
DMAP
DMAP
DMAP
DMAP
DMAP
-
DCE
DCE
DCE
DCE
DCE
Toluene
Hexane
CH3CN
DMF
Dioxane
DCE
DCE
DCE
DCE
DCE
DCE
DCE
DCE
DCE
Cu(OAc)2·H2O
Cu(OAc)2·H2O
Cu(OAc)2·H2O
Cu(OAc)2·H2O
Cu(OAc)2·H2O
Cu(OAc)2·H2O
Cu(OAc)2·H2O
Cu(OAc)2·H2O
Cu(OAc)2·H2O
Cu(OAc)2·H2O
-
NiCl2
ZnCl2
Cu(OAc)2
FeCl3
BF3·O(C2H5)2
BF3·O(C2H5)2
BF3·O(C2H5)2
BF3·O(C2H5)2
Cu(OAc)2·H2O
Cu(OAc)2·H2O
Cu(OAc)2·H2O
120
120
120
120
120
120
120
120
120
120
120
120
120
120
120
120
100
80
9
39
84
66
46
65
41
78
trace
71
0
O
O
O
N
Cl
Cl
Cl
N
N
N
R2
N
R
N
R1
3q, R = 3,5-Me2C6H3 (70%)
3r, R = 2,4,6-Me3C6H2 (53%)
3s, R = 3,5-F2C6H3 (73%)
3t, R = 2,3-Cl2C6H3 (69%)
3u, R = 1-naphthyl (80%)
3v, R = 2-naphthyl (61%)
3w, R = 2-thienyl (63%)
3x, R = Me (43%)
3ba, R2 = 7-Me (60%)
3bb, R2 = 6-Cl (70%)
3bc, R2 = 6-Br (75%)
3bd, R2 = 7-Br (68%)
3be, R2 = 5-F (43%)
3a, R1 = H (84%)
3b, R1 = 2-Me (66%)
3c, R1 = 3-Me (85%)
3d, R1 = 4-Me (78%)
3e, R1 = 3-OMe (68%)
3f, R1 = 4-OMe (65%)
3g, R1 = 4-Et (83%)
3h, R1 = 2-F (74%)
3i, R1 = 3-F (86%)
0
42
79
0
19
12
trace
trace
50
59
66
3y, R = isopropyl (53%)
3aa, R = tertbutyl (trace)
-
-
60
80
100
140
3j, R1 = 4-F (79%)
DMAP
DMAP
DMAP
DCE
DCE
DCE
O
3k, R1 = 2-Cl (75%)
3l, R1 = 3-Cl (78%)
3m, R1 = 4-Cl (79%)
3n, R1 = 4-Br (77%)
3o, R1 = 3-CF3 (69%)
3p, R1 = 4-CH2Cl (66%)
Cl
N
a
N
Reaction conditions: aryl-oxazoline 1a (0.1 mmol), 2 (0.13 mmol), base (0.02
mmol), Lewis acid (0.02 mmol), solvent (1.0 mL), 120 °C under air for 10 h.
Isolation yield.
b
3z, 51%
a Reaction conditions: aryl-oxazoline 1a (0.1 mmol), 2 (0.13 mmol), Cu(OAc)2·H2O
(0.02 mmol), DMAP (0.02 mmol), DCE (1.0 mL), 120 °C under air for 10 h. b Isolation
yield.
carbon-carbon and carbon-heteroatom bonds because of the
presence of the bidentate auxiliary directing group.21 Thus, their
development and utilization have attracted significant interest
in the chemical community. Herein, we performed the synthesis
of quinazolinones from amide-oxazolines with TsCl.
We began our experiment with the reaction of 2-(4,5-
dihydrooxazol-2-yl) aniline, benzoyl chloride with TsCl, but the
experimental results were not satisfactory (see supporting
information for details). We had to choose amide-oxazoline (1a)
and TsCl as model substrates, and screened different solvents,
temperatures, bases and Lewis acids (Table 1).
Initially, the reaction was performed in the presence of
Cu(OAc)2·H2O (0.02 mmol) and K2CO3 (0.02 mmol) in DCE (1.0
mL) at 120 °C for 10 h. As expected, the desired reaction took
place, leading to the formation of the product 3a in 9% yield
(Table 1, entry 1). A series of bases were then examined (entries
1-5), and the results showed that the DMAP provided the
highest yield of 84% (entry 3). The product was still obtained
with 46% yield even in the absence of a base (entry 5). Various
solvents, including non-polar solvents (toluene and hexane) and
polar solvents (DMF, dioxane and CH3CN), were also tested
(entries 6-10). However, DCE was found to be the best solvent
for this reaction. The effects of different Lewis acids were also
investigated (entries 11-16). The yield did not change
significantly with different Lewis acids. However, no product
was obtained in the absence of a Lewis acid, indicating that a
Lewis acid is necessary for the reaction (entry 11). In addition,
we also conducted a series of reactions with BF3·O(C2H5)2 at a
lower temperature without adding DMAP (entries 17-19). To
further improve the yield of the reaction, different reaction
temperatures were used. Unfortunately, no improvement in
the reaction yield was found (entries 20-21). Furthermore,
several “Cl” sources (e.g., NH4Cl, KCl, NaCl and NCS) were used.
However, under these conditions, no appreciable amount of
product was produced (for details see the Supporting
Information).
The optimized reaction conditions (Table 1, entry 3) were
then used to assess the scope and generality of this reaction for
producing quinazolinones (Table 2). First, R-substituted aryl
amide-oxazoline substrates with different substituents were
evaluated (3b-3w). Mono-substituted (ortho-, para- and meta-)
aryl amide-oxazoline substrates (3b-3p) with electron-donating
groups or electron-withdrawing groups afford the desired
products with moderate to good yields of 65−86%. Remarkably,
for poly-substituted aryl amide-oxazoline substrates (3q-3t),
the corresponding products 3r were only obtained with 53%
yield. This is probably due to a small amount of steric hindrance.
It is worth noting that the substituents in 1-naphthylamide-
oxazoline and 2-naphthylamide-oxazoline survived the reaction
and the desired quinazolinones were obtained in 80% and 61%
yield (3u-3v). Interestingly, the reaction of heteroatom-
substituted 2-thiopheneamide-oxazoline with TsCl also
provided the homologous heterocyclic compound 3w in 63%
yield. We subsequently extended the reaction to R-substituted
alkyl amide-oxazolines under the optimized conditions (3x-3aa).
Unexpectedly, those substrates showed lower reactivity,
providing the desired products in 43-53% yields (3x-3z).
However, the desired product 3aa was not observed, most
likely due to the high steric hindrance. Finally, we explored R2-
2 | J. Name., 2012, 00, 1-3
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Table 3 Investigation of other sulfonyl chlorides.
Then, electron transfer occurs to remove the LAVaienwdArt-iTclseOOn- litnoe
obtain
DOI: 10.1039/D0OB00225A
O
S
O
S
O
S
O
S
Cl
O
Cl
O
Cl
O
Cl
O
OTs
TsCl
1a + LA
N
MeO
Cl
F
F3C
N
N
N
N
Ts
N
O
LA
A1
A, 69%
B, 72%
D, 75%
C, 77%
N
N
S1
O
S
Cl
NH2
O
O
O
F3C S Cl
O
Cl S Cl
O
F, 0%
E, 9%
G, (no product)
OTs
Ph
LA
N
Cl
OTs
O
N
N
N
DCE, 120oC, 10h
DMAP (0.2 equiv)
Cu(OAc)2 H2O (0.2 equiv)
O
N
Cl
O
O
N
O
-OTs
-LA
LA
N
Ph
Cl
N
N
H
A2
A4
A3
Cl
+
TsCl
N
O
TEMPO (1.2 equiv): 51%
galvinoxyl (1.2 equiv): 71%
1a
2
3a
Cl
O
DCE, 120oC, 10h
DMAP (0.2 equiv)
Cu(OAc)2 H2O (0.2 equiv)
Cl
O
O
N
3a
Cl
N
N
Ph
N
N
A5 (1,3-azaoxonium)
N
Ph
A4
Scheme 3 Plausible mechanistic pathways.
3a (78%)
Scheme 2 Control experiments.
intermediate A4, followed by a 1,3-O → N shift of the
chloroethyl groups via a cyclic 1,3-azaoxonium intermediate
(A5), giving the desired product 3a.
substituted aryl amide-oxazoline substrates (3ba-3be).
Obviously, the substrates 3ba-3bd show moderate to good
yields (60-75%). However, the yield of substrate 3be is
significantly reduced.
The effects of other sulfonyl chlorides were also examined.
Para-substituted benzenesulfonyl chlorides (Table 3, A-D) gave
the target product 3a in 69-77% yield. However, substrate E
only provided a yield of 9% of the product 3a and substrate F
failed to produce the corresponding product. Furthermore,
substrate G could not afford the corresponding product 3-(2-
aminoethyl)-2-phenylquinazoline-4(3H)–one.
In conclusion, we have developed an efficient, operationally
simple and practical one-pot process for the synthesis of
quinazolinone derivatives via 6π electron cyclization of amide-
oxazolines with TsCl in the presence of DMAP and a Lewis acid.
This methodology not only tolerates a range of functional
groups, affording the desired products in moderate to good
yields, but also enriches the construction of quinazolinone
derivatives.
To obtain evidence about the mechanism of this reaction, a
series of control experiments were carried out, as shown in
Scheme 2. First, a stoichiometric amount of the radical inhibitor
TEMPO (2,2,6,6-tetramethylpiperidine-N-oxyl) and galvinoxyl
were used under the optimal reaction conditions. In the
presence of these radical inhibitors, the target product 3a was
obtained with 51% and 71% yield, respectively. This shows that
a free radical pathway is not involved in the reaction. In
addition, we selected A4 as the initial substrate and obtained
the target product 3a under standard conditions with a yield of
78%. Additionally, the potential intermediates A4 and A1 were
detected by HRMS-ESI (see the Supporting Information), which
further validates our proposed mechanism.
Based on these results and the literature data,22 we propose
a plausible mechanism for the reaction of amide-oxazolines
with TsCl to produce quinazolinones (Scheme 3). The reaction
initially transfers a -Ts group from TsCl to DMAP to form
intermediate S1, which reacts with 1a and the Lewis acid (LA) to
produce intermediate A1, with loss of DMAP. Subsequently, Cl-
attacked the intermediate oxazoline in A1 to produce
intermediate A2. A2 further undergoes a 6π electron
cyclization, resulting in the generation of intermediate A3.
Conflicts of interest
There are no conflicts to declare.
Notes and references
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