Sulfur-Promoted Synthesis of 2-Aroylquinazolin-4(3H)-ones by Oxidative Condensation of Anthranilamide and Acetophenones

Article abstract of DOI:10.1002/adsc.201900371

A sulfur-promoted three-component reaction of isatoic anhydride, primary aliphatic or aromatic amines, and acetophenones leading to densely substituted 3-substituted 2-aroylquinazolin-4(3H)-ones is reported. The key step involves a cascade reaction of selective oxidation of the methyl group of the acetophenones, followed by a condensation with anthranilamides. The scope of the reaction is applicable to the synthesis of tryptanthrin and various 3-unsubstituted 2-aroylquinazolin-4(3H)-ones. (Figure presented.).

Full text of DOI:10.1002/adsc.201900371

Title: Sulfur-Promoted Synthesis of 2-Aroylquinazolin-4(3H)-ones by
Oxidative Condensation of Anthranilamide and Acetophenones
Authors: Thanh Binh Nguyen, Jing-ya Hou, and pascal retailleau
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To be cited as: Adv. Synth. Catal. 10.1002/adsc.201900371
Link to VoR: http://dx.doi.org/10.1002/adsc.201900371

10.1002/adsc.201900371
Advanced Synthesis & Catalysis
COMMUNICATION
DOI: 10.1002/adsc.201((will be filled in by the editorial staff))
Sulfur-Promoted Synthesis of 2-Aroylquinazolin-4(3H)-ones by
Oxidative Condensation of Anthranilamide and Acetophenones
Thanh Binh Nguyen,* Hou Jing-ya, and Pascal Retailleau
Institut de Chimie des Substances Naturelles, CNRS UPR 2301, Université Paris-Sud, Université Paris-Saclay, 1
avenue de la Terrasse, 91198 Gif-sur-Yvette, France
Email: thanh-binh.nguyen@cnrs.fr
Received: ((will be filled in by the editorial staff))
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201######.((Please
delete if not appropriate))
best of our knowledge, this is the first report of
general sulfur-promoted oxidative coupling between
weakly nucleophilic and sterically hindered N-
substituted 2-aminobenzamides with acetophenones.
More importantly, we expand this concept to N-
unsubstituted 2-aminobenzamides.
Abstract. A sulfur-promoted three-component reaction
of isatoic anhydride, primary aliphatic or aromatic
amines, and acetophenones leading to densely
substituted 3-substituted 2-aroylquinazolin-4(3H)-ones
is reported. The key step involves a cascade reaction of
selective oxidation of the methyl group of the
acetophenones, followed by a condensation with
anthranilamides. The scope of the reaction is applicable
to the synthesis of tryptanthrin and various 3-
unsubstituted 2-aroylquinazolin-4(3H)-ones.
In 2013, Wu et al. reported an I2/DMSO promoted
oxidative
coupling
reaction
between
2-
aminobenzamides with acetophenones to provide a
range of 3-unsubstituted 2-benzoylquinazolin-4-ones
(Scheme 1).[5] Because of a side reaction between
molecular iodine with 2-aminobenzamides leading to
their 5-iodinated derivatives, the iodination step of
acetophenones should be performed prior to the
addition 2-aminobenzamides. Moreover, it appears
that this approach is working well when the amide
Keywords: sulfur; anthranilamide; acetophenone,
DMSO; oxidative condensation
Aza heterocycles constitute core structural function of 2-aminobenzamides is not substituted.
components in a variety of natural products and Indeed, the yields of N-methyl amides derivatives
biologically active compounds. Quinazolin-4(3H)-one
scaffold in particular are not only ubiquitous in
biologically active molecules[1] but also present in a
diverse set of natural products (Figure 1).[2]
Consequently, an increasing number of new
methodologies have been developed to enhance the
occurrence of the quinazolin-4(3H)-one scaffold in
corporate compound collections for biological
evaluations.[3] In order to increase the lipophilicity as
well as the activity of quinazolin-4(3H)-ones, one of
the simplest strategies is to incorporate an alkyl or
aryl substituents to the N-3 position.[4]
were described to be generally lower than that of their
NH2 amide analogues and no other larger substituents
were reported.
Scheme 1. 2-Aroylquinazolin-4(3H)-ones
Anthranilamides 3 and Methyl Ketones 2
4
from
Here, we propose an alternative strategy based on
the use of elemental sulfur[6] as an oxidant applicable
to anthranilamides 3 bearing a wide range of alkyl
and aryl substituent on the amide group.
For this purpose, we started the optimization
studies based on the oxidative coupling reaction
between 2-aminobenzanilide 3a with acetophenone
2a in the presence of elemental sulfur (twice the
stoichiometric amount) as oxidant (Table 1). The
Figure 1. Selected 2-Aryl-3-Aroylquinazolin-4(3H)-ones
Herein, we describe a convenient access to 3-
substituted 2-aroylquinazolin-4(3H)-ones 4 base on
three component one-pot two-step reaction of isatoic
anhydride, primary aliphatic or aromatic amines, and
acetophenones 2 promoted by elemental sulfur. To the
1
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10.1002/adsc.201900371
Advanced Synthesis & Catalysis
reaction between the three components under neat with halogeno groups (products 4c, 4d and 4i) and
condition (entry 1) or in a small amount of DMSO at with sterically hindered substituent at the ortho
100 ºC did not lead to the expected product 4a. position of the anilines (products 4e-g).
Gratifyingly, in the presence of N-methylpiperidine,
which was previously identified as an excellent sulfur
activator,[7] we observed the formation of
quinazolinone 4a (entry 3), especially in the presence
of DMSO[4d] (entries 5-7). The reaction worked well
with a slight excess of sulfur (entry 7). However,
although DMSO was thought to act as co-oxidant,
reaction with stoichiometric or sub-stoichiometric
amount of sulfur (entries 8-9) resulted in lower yields.
Finally, we found that the reaction is less efficient
with lower N-methylpiperidine amount (entry 10) or
at lower temperature (entry 11).
Table 1. Optimization of the Reaction Conditions
Entrya
1
2
3
4
5
6
7
x
6
6
6
6
6
6
4
3
2
4
4
y
0
0
1
1
1
1
1
1
1
0.5
1
z
0
0.1
0
0.1
0.2
0.5
0.5
0.5
0.5
0.5
0.5
Temp (°C)
100
100
100
100
100
100
100
100
Yield (%)b
0c
0c
25
45
67
70
75
67
35
45
38
8
9
100
100
80
10
11
a Reaction conditions: 2-aminobenzanilide 3a (1 mmol, 212
mg), acetophenone 2a (1.2 mmol, 144 mg), sulfur (x mmol,
32 mg/mmol), N-methylpiperidine (y mmol), DMSO (z
mL), 80-100 °C, 16 h. Isolated yield. Determined by 1H
b
c
NMR.
Next, the optimized conditions (entry 7) were
adapted to the syntheses of other quinazolinones 4
(Scheme 2). Since most of N-substituted 2-
aminobenzanilides were not commercially available,
we developed a convenient access to such compounds
based on thermal, uncatalyzed and solvent-free
reaction
between
isatoic
anhydride
with
stoichiometric amounts of amine.[8]
The decarboxylative coupling with aromatic
amines 1 with isatoic anhydride under solvent free
conditions was performed at 130-150 °C for 1-3 h.
Gratifying, once the process was completed, the CO2
evolution ceased. Acetophenone, sulfur, N-
methylpiperidine and DMSO were subsequently
added and the reaction mixtures were further heated at
100 °C for 16 h. One-pot reaction of unsubstituted
aniline led to the expected product 4a in slightly
lower yield (75% vs 70%). Similarly, p-anisidine
provided the desired product 4b in excellent yield.
Gratifyingly, the optimal conditions were compatible
2
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10.1002/adsc.201900371
Advanced Synthesis & Catalysis
Scheme 2. One-pot Synthesis of Quinazolinones 4 from
Isatoic Anhydride, Amines 1 and Methyl Ketones 2
Importantly, heteroaromatic amine such as 3-
aminopyridine could successfully be incorporated into
the quinazolinone 4i, albeit with a diminished yield.
Subsequently, the one-pot protocol was applicable to
substituted acetophenones and their heteroaromatic
analogues 3-pyridyl and 2-thienyl to provide products
4l-4o in reasonable yields. Although the reaction of
alkyl methyl ketones (2-pentanone or 2-heptanone)
seems to be complicated (results not shown), we were
able to obtain the product 4p from pinacolone. In this
case, despite the low yield, the reaction mixture
remained clean, suggesting undoubtedly that the t-
butyl group slowed the conversion process.[9] When o-
phenylenediamine was used as starting amine, fused
tetracyclic compound 4q was formed in good yield.
Its structure was confirmed via X-ray crystallography.
Interestingly, our strategy could be applied to the
synthesis of tryptanthrin. For this purpose, o-
aminoacetophenone was used as the amine
component. Due to unfavorable electron withdrawing
effect of the acetyl group as well as its steric
hindrance, the decarboxylative coupling step should
be performed at 160 ºC to ensure significant CO2
evolution. Subsequent intramolecular oxidative
condensation providing tryptanthrin could be
achieved under the standard conditions. Despite low
global yield in which the first step of formation of the
corresponding anthranilamide could be improved, this
result showed that the reaction could be realized in an
intramolecular version.
Scheme 3. Synthesis of NH Quinazolinones 6
At this stage, with highly general and simple
conditions in place, we focused our attention on the
reaction of N-unsubstituted anthranilamides
(Scheme 3). Thus, we employed this substrate in the
reaction with a range of acetophenones.
6
When primary aliphatic amines were used as the
amine components, the formation of the
corresponding substituted anthranilamides could be
performed at significantly lower temperatures (rt-60
ºC). Subsequent oxidative condensation with
acetophenone led to the final products 4r-4t in high
yields.
This approach led to the synthesis of 3-NH-
quinazolin-4-ones 6a-6i in moderate to good yields
(43–75%). In general, acetophenone itself as well as
its analogues p-substituted by an electron donating
group gave better yields (6a-6d). On the other hand,
p-cyanoacetophenone displayed lower reactivity
(product 6e). Although the byproduct of the reaction,
i.e. hydrogen sulfide, is known to add to the nitrile
group to yield thioamide, such a reaction did not
happen under the present conditions. Other m-
substituted acetophenones afforded the expected
quinazolin-4-ones 6f-6i in moderate yields. The
structure of quinazolinone 6g derived from m-
chloroacetophenone was confirmed unambiguously
by X-ray crystallography. Interestingly, the reaction
proceeded in similar fashion with other
heteroaromatic methyl ketones.
Introducing an o-chloro group on the aromatic ring
of the acetophenone moiety afforded the products in
lower yield (6j). This observation suggested that the
efficiency of the oxidative coupling process depends
also on the steric hindrance of the methyl ketone
moiety.[10] Additionally, heteroaryl methyl ketones
such as 2-acetylthiophene and 3-acetylpyridine
afforded the corresponding products 6k-6l in
reasonable yields. Once again, pinacolone exhibited a
lower reactivity. It should be however noted that such
3
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10.1002/adsc.201900371
Advanced Synthesis & Catalysis
an example was not reported with molecular iodine- strategy in the one-pot synthesis of natural
promoted method.[6]
quinazolinone tryptanthrin. This new procedure of
sulfur-promoted oxidative coupling of anthranilamide
5 with methyl ketones 2 was also successfully utilized
to prepare NH 2-aroylquinazolin-4-ones 6. Further
exploration of new reactivities of elemental sulfur in
organic chemistry and applications are currently in
progress in our laboratory.
Experimental Section
One-pot procedure for the synthesis of quinazolinones 4
from isatoic anhydride, amines 1 and methyl ketones 2
From aromatic amines: A mixture of isatoic anhydride 1
(1 mmol), and aromatic amine (1.05 mmol) was heated
with magnetic stirring at 130-150 °C for 1-3 h in a 7-mL
glass test tube closed with a rubber septum under an argon
atmosphere. The CO2 gas formed during the course of the
reaction was evacuated by mean of a rubber argon balloon.
When the evolution of CO2 ceased, sulfur (4 mmol, 128
mg), methyl ketone (1.2 mmol), N-methylpiperidine (1
mmol, 99 mg), and DMSO (0.5 mL) were added and the
reaction tube was closed again, flushed with argon and
heated at 100 °C for 16 h. The reaction mixture was
purified by column chromatography on silica gel.
From aliphatic amines: Aliphatic amine (1.05 mmol) was
added to a mixture of isatoic anhydride 1 (1 mmol) in
DMSO in a 7-mL glass test tube. The resulting mixture was
stirred at rt for 5-10 min, the tube was next closed with a
rubber septum under an argon atmosphere. The CO2 gas
formed during the course of the reaction was evacuated by
mean of a rubber argon balloon. The tube was heat at 60 °C.
When the evolution of CO2 ceased, sulfur (4 mmol, 128
mg), methyl ketone (1.2 mmol), and N-methylpiperidine (1
mmol, 99 mg) were added and the reaction tube was closed
again, flushed with argon and heated at 100 °C for 16 h.
The reaction mixture was purified by column
chromatography on silica gel.
Scheme 4. Proposed Mechanism
Based on the results previously reported by our
group,[7] we proposed a plausible mechanism depicted
in Scheme 4. The formation of quinazolinone 6 could
proceed via two possible pathways. In the first
pathway,[7c] methyl ketone 2 would react with sulfur
activated by N-methylpiperidine according to
Willgerodt type mechanism. While its methyl group
is oxidized and trapped with anthranilamide 5 to form
an amidine moiety, its ketone group is reduced into a
methylene group to yield quinazolinone A.[11]
Oxidation of the benzylic by S/DMSO would lead to
the final product 6. Alternatively, the methyl group of
ketone 2 could be directly oxidized by sulfur to
aldehyde B, which could subsequently condense with
5 to provide aminal C and then quinazolinone 6. In
both pathways, the oxidation of A and C to 6 could be
favored by the formation of the tautomers A’ from A
and C’ from C.
Procedure for the synthesis of quinazolinones 6 from
anthraniliamide 5 and methyl ketones 2
A mixture of anthranilamide 5 (1 mmol 136 mg), sulfur (4
mmol, 128 mg), methyl ketone 2 (1.2 mmol), N-
methylpiperidine (1 mmol, 99 mg) and DMSO (0.5 mL)
was heated in a 7-mL glass test tube under an argon
atmosphere at 100 °C for 16 h. The reaction mixture was
purified by column chromatography on silica gel.
CCDC-1881910 and CCDC-1881911 (compounds 6g and
4p
respectively)
contain
the
supplementary
crystallographic data for this paper. These data can be
obtained free of charge from The Cambridge
Crystallographic
www.ccdc.cam.ac.uk/data_request/cif.
Data
Centre
via
To confirm the oxidation step of A to 6, A1 (Ar =
Ph) was synthesized independently[12] and allowed to
react under the same conditions. The formation of 6a
in moderate yield in the presence of both sulfur and
DMSO as oxidants suggested the feasibility of this
pathway.
Acknowledgements
We thank ICSN-CNRS and Dr. A. Marinetti (ICSN-CNRS) for
helpful support.
In summary, we have developed a one-pot two-step
three-component reaction of isatoic anhydride,
primary aliphatic or aromatic amines 1, and methyl
ketones 2 (acetophenones or pinacolone) promoted by
elemental sulfur to provide a range of 3-substituted 2-
aroylquinazolin-4(3H)-ones 4. The use of o-
aminoacetophenone as both amine and methyl ketone
component has provided a proof-of-concept of our
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Advanced Synthesis & Catalysis
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5
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10.1002/adsc.201900371
Advanced Synthesis & Catalysis
COMMUNICATION
Sulfur-Promoted Synthesis of 2-Aroylquinazolin-
4(3H)-ones by Oxidative Condensation of
Anthranilamide and Acetophenones
S8
R
O
O
3N
N
O
O
R
N-methylpiperidine
N
+
H3C
R’
H
R’
DMSO
100 ºC, 16 h
NH2
ArNH2
or
AlkNH2
34 examples
R = Ar, Alkyl, H
R’ = Ar, t-Bu
one-pot
Adv. Synth. Catal. Year, Volume, Page – Page
O
N
isatoic anhydride
N
Thanh Binh Nguyen,* Hou Jing-ya, and Pascal
Retailleau
O
tryptanthrin
6
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