One-pot synthesis of 2-substituted quinoxalines using K10-montmorillonite as heterogeneous catalyst

Article abstract of DOI:10.1016/j.tetlet.2014.01.087

An efficient one-pot synthesis of 2-substituted quinoxalines from 1,2-diamines and phenacyl bromides is developed using K10-montmorillonite (K10 clay) as a catalyst at 50 C in acetonitrile medium. This method offers an easy route for the synthesis of subs

Full text of DOI:10.1016/j.tetlet.2014.01.087

Tetrahedron Letters 55 (2014) 1616–1620
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Tetrahedron Letters
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One-pot synthesis of 2-substituted quinoxalines using
K10-montmorillonite as heterogeneous catalyst
Mariappan Jeganathan a, Amarajothi Dhakshinamoorthy a,b, Kasi Pitchumani a,b,
⇑
a School of Chemistry, Madurai Kamaraj University, Madurai 625 021, India
b Centre for Green Chemistry Processes, School of Chemistry, Madurai Kamaraj University, Madurai 625 021, India
a r t i c l e i n f o
a b s t r a c t
Article history:
An efficient one-pot synthesis of 2-substituted quinoxalines from 1,2-diamines and phenacyl bromides is
developed using K10-montmorillonite (K10 clay) as a catalyst at 50 °C in acetonitrile medium. This
method offers an easy route for the synthesis of substituted quinoxalines in high yields. A plausible
mechanism is proposed in which quinoxalines are formed via dehydration–dehydrohalogenation–
cyclization sequence. Further, the K10 clay catalyst is recovered by simple filtration and reused six times
without any loss in its catalytic activity.
Received 26 November 2013
Revised 17 January 2014
Accepted 21 January 2014
Available online 28 January 2014
Keywords:
Ó 2014 Elsevier Ltd. All rights reserved.
Quinoxalines
K10-montmorillonite
Solid acids
1,2-Diamines
a-Bromoketones
Synthesis of quinoxalines and their derivatives is receiving
reagents, and the requirement of high temperature to conduct
the reaction. In particular, acetic acid and perchloric acid are more
hazardous and the current trend is to develop green and sustain-
able protocols toward the same.
considerable attention due to their biological activities and
pharmaceutical applications.1 Quinoxalines have been used in
anticancer,2 antiviral,3 antibiotic (echinomycin, leromycin and
actinomycin) anti-inflammatory, and kinase inhibition activities.4
Furthermore, they are also used as potential building blocks for
the synthesis of organic semiconductors,5 electroluminescent
materials,6 cavitands,7 dehydroannulenes,8 and dyes.9
In this context, considerable attention has been devoted to per-
form organic transformations using solid acids as heterogeneous
catalysts.25 In the present work, we report a new synthetic strategy
for the synthesis of quinoxaline derivatives catalyzed by K10 clay
under mild reaction conditions. K10 clay is a layered alumina-
silicate clay with a dioctahedral layer sandwiched between two
tetrahedral layers.26 K10 clay with a moderate acid strength and
a surface area of 250 m2/g can be used as heterogeneous catalyst
for various organic transformations due to their tunable Bronsted
and Lewis acidities27a,b and is considered to be an environmentally
benign solid acid catalyst that offers several advantages, such as
ease of handling, non-corrosiveness, low cost, and reusability.
The reaction conditions were optimized28 for the synthesis of
2-phenylquinoxaline using o-phenylenediamine and phenacyl
bromide as model substrates and the observed results are given
in Table 1. Blank control experiments in the absence of catalyst
showed 8% and 17% of product at room temperature and 50 °C in
8 and 3 h respectively in acetonitrile medium (Table 1, entries 1
and 2). In the absence of solvent, K 10 clay gave 13% and 69% yields
at room temperature and 50 °C respectively in 3 h (Table 1, entries
3 and 4). Further increasing the reaction time to 6 h at 50 °C
improved the yield to 77% (Table 1, entry 5) and it can be
considered as an encouraging result, from the green and sustain-
able process since it does not require any solvent in the reaction
A number of methods have been developed for the synthesis of
quinoxalines. One such method involves the condensation of a
1,2-diketone with aryl-1,2-diamine to give the corresponding
quinoxaline at refluxing temperature in ethanol, benzene, or acetic
acid.10 This reaction is catalyzed by iodine,11 indium(III) chloride,12
copper(II) sulfate,13 ceric ammonium nitrate,14 o-iodoxybenzoic
acid,15 phosphorus oxychloride,16 silica gel,17 gallium(III) tri-
flate,18a and clayzic.18b On the other hand, 1,4-addition of the
1,2-diamines to diazenylbutenes19 and oxidation of
a-hydroxyke-
tones with 1,2-diamines20 have also been reported for the synthe-
sis of the corresponding quinoxalines. Also, the synthesis of
quinoxaline has been reported by the reaction of 1,2-diamines
with substituted phenacyl bromides in solid phase,21 and using
catalysts like perchloric acid supported on silica,22a trimethylsilyl
chloride,22b KF-alumina,22c b-cyclodextrin,23 and 1,4-diazabicyclo
[2,2,2]octane.24 However, these reported procedures suffer from
limitations such as the need of excess catalyst loading, toxic
⇑
Corresponding author. Tel.: +91 452 2456614; fax: +91 452 2459181.
E-mail address: pit12399@yahoo.com (K. Pitchumani).
http://dx.doi.org/10.1016/j.tetlet.2014.01.087
0040-4039/Ó 2014 Elsevier Ltd. All rights reserved.

M. Jeganathan et al. / Tetrahedron Letters 55 (2014) 1616–1620
1617
Table 1
Optimization of reaction conditions for the synthesis of 2-phenylquinoxalinea
O
N
N
NH2
NH2
+
Br
Entry
Catalyst
Solvent
Time (h)
Temp (° C)
Yieldb (%)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
—
—
ACN
ACN
None
None
None
ACN
ACN
ACN
ACN
ACN
ACN
Methanol
Methanol
Methanol
Methanol
Methanol
THF
8
3
3
3
6
3
8
0.5
1
2
3
0.5
1
2
3
6
3
3
rt
50
rt
50
50
rt
8
17
13
69
77
33
90
18
40
71
92
10
29
56
80
82
85
75
70
68
59
60
62
K10 clay
K10 clay
K10 clay
K10 clay
K10 clay
K10 clay
K10 clay
K10 clay
K10 clay
K10 clay
K10 clay
K10 clay
K10 clay
K10 clay
K10 clay
K10 clay
K10 clay
K10 clay
K10 clay
K10 clay
K10 clay
rt
50
50
50
50
50
50
50
50
50
50
50
50
50
50
50
50
Figure 2. Effect of catalyst loading on the yield of 2-phenyl quinoxaline. Reaction
conditions: o-phenylenediamine (1 mmol), phenacyl bromide (1 mmol), K10 clay,
CH3CN (5 mL), 50 °C, 3 h.
catalyst loading. Further increase of catalyst amount fails to in-
crease the yield suggesting an optimal value of catalyst loading
for this reaction under the present experimental conditions.
These interesting results observed in the synthesis of 2-phenyl-
quinoxaline in high yield under mild reaction conditions encour-
aged us to check the generality of this methodology using a wide
variety of 1,2-diamines and phenacyl bromides. Under the opti-
mized conditions, both electron rich and electron deficient substit-
uents on diamines and phenacyl bromides resulted in high yield of
quinoxaline derivatives (Table 2). For example, the reaction of o-
phenlyenediamine with phenacyl bromide containing electron-
donating (4-OMe) and electron-withdrawing (3-Br, 3-F, 4-NO2)
substituents resulted in high yields of substituted quinoxalines
(Table 2, entries 2–5). On the other hand, substituted o-phenylen-
ediamines also gave the corresponding 2-substituted quinoxalines
with various phenacyl bromides in high yields (Table 2, entries 6–
13). Increasing the molecular dimension of 1,2-diamine as in the
case of 3,4-diaminobenzophenones, (Table 2, entries 14–17) with
various phenacyl bromides has also resulted in very high yield of
the desired products. It is also interesting to note that condensa-
tion between the ketone and the amino group is not observed un-
der the present experimental conditions. It is very clear from the
observed results that the nature of the substituents, steric hin-
drance, and molecular dimension of the reactants have a minimal
role to play in determining the rate of reaction and as a result, most
of the reactions afforded very high yields under mild reaction con-
ditions. Thus, the operational simplicity of the process, achieving
the desired products in high yields regardless of the kind of start-
ing materials, low cost of the catalyst, and the use of acetonitrile as
solvent make this protocol an alternative green chemical process
for the already existing methodologies.
One of the main advantages of using heterogeneous catalysts
such as K10 clay is that they can be recovered and reused effi-
ciently. In this context, the reusability of K10 clay was checked
in the synthesis of 2-phenylquinoxaline under optimized condi-
tions, as given in Table 1. After completion of the reaction, the cat-
alyst was recovered by filtration, washed thoroughly with
acetonitrile and dried at 80 °C for 3 h. The recovered catalyst was
used for consecutive runs under identical reaction conditions and
the observed results are given in Table 3. Hence, the catalyst exhib-
ited high activity up to six reuses with only a marginal decrease in
the yield which may be caused from the loss of catalyst during
recycling or adsorption of organic products over the catalyst by
poisoning their active sites. In any case, this catalyst exhibited high
potential by maintaining its activity while recycling experiments.
Chloroform
Acetone
Dichloromethane
DMF
Benzene
Toluene
3
3
3
3
3
a
Reaction conditions: o-phenylenediamine (1 mmol), phenacyl bromide
(1 mmol), K10 clay (50 mg), solvent (5 mL).
b
Isolated yield.
process. K10 clay showed highest yield of 92% in acetonitrile in 3 h
while methanol gave 80% under identical conditions (Fig. 1) and no
further increase in yield was noticed even after 6 h (Table 1, entries
8–16). Further, the reactions were performed using acetonitrile as
a solvent only from the perspective of yield but however perform-
ing reactions in methanol or under solvent-less conditions is
potentially more interesting from green and sustainable processes
points of view. On the other hand, 90% yield (Table 1, entry 7) of
the desired product was obtained in acetonitrile at room tempera-
ture in 8 h. Moderate to high yields were achieved with conven-
tional organic solvents (Table 1, entries 17–23).
On the other hand, efforts were also made to optimize the cat-
alyst loading in this reaction and the observed results are given in
Fig. 2. It can be seen very clearly that the percentage yield gradu-
ally increased from 15 to 50 and reaches a maximum at 75 mg of
100
(a)
(b)
80
60
40
20
0
0.0 0.5 1.0 1.5 2.0 2.5 3.0
Time (h)
Figure 1. Time conversion plot for the synthesis of 2-phenylquinoxaline in
acetonitrile (a) and methanol (b); reaction conditions: o-phenylenediamine
(1 mmol), phenacyl bromide (1 mmol), K10 clay (50 mg), solvent (5 mL), 50 °C.

1618
M. Jeganathan et al. / Tetrahedron Letters 55 (2014) 1616–1620
Table 2
Synthesis of various substituted quinoxalines in the presence of K10 clay as heterogeneous catalysta
Entry
1
Diamine
NH2
Phenacyl bromide
Quinoxaline
Yieldb (%)
92
O
N
N
NH2
Br
O
NH2
NH2
N
N
2
90
Br
H3CO
OCH3
Br
NH2
NH2
O
N
N
Br
3
4
95
91
Br
NH2
NH2
O
N
N
F
F
Br
O
NH2
NH2
N
N
5
6
7
93
89
85
Br
O2N
NO2
NO2
NH2
O
NO2
N
Br
NH2
N
NO2
NH2
O
NO2
N
Br
Br
O
Br
Br
NH2
N
NO2
NH2
NO2
N
8
86
Br
Br
NH2
N
Cl
NH2
NH2
O
Cl
N
N
9
87
91
93
Br
Br
Br
Cl
NH2
O
N
N
Cl
10
11
NH2
Br
O
NH2
NH2
N
N
Br
Br
Br
N
H3COOC
NH2
NH2
O
H3COOC
12
13
N
87
89
Br
H3CO
OCH3
Cl
H3COOC
O
NH2
NH2
O
H3COOC
O
N
N
Cl
Br
O
NH2
N
N
14
15
Br
83
86
NH2
H3CO
OCH3
O
O
O
O
O
NH2
NH2
N
N
Br
Br
Br
O
NH2
NH2
N
N
16
17
Br
87
85
O2N
NO2
O
O
O
NH2
NH2
N
N
Br
a
Reaction conditions: diamine (1 mmol), phenacyl bromide (1 mmol), K10 clay (50 mg), acetonitrile (5 mL), 50 °C, 3 h.
Isolated yield.
b
The surface acidity of natural clays with Na+ and NH4þ as inter-
by IR studies using adsorption of ammonia as a probe molecule.
Two absorption bands have been observed at 1445 and
1630 cmꢀ1. The band at 1630 cmꢀ1 was attributed to the bending
stitial cations ranges from +1.5 to ꢀ3 on Hammett scale.27c The
presence of Lewis and Bronsted acid sites has been reported earlier

M. Jeganathan et al. / Tetrahedron Letters 55 (2014) 1616–1620
1619
Table 3
with aromatization as the driving force. The clay catalyst is re-
leased for further cycle of reaction.
Reusability of K10 clay in the synthesis of 2-phenylquinoxalinea
The activity and efficiency of the present work are compared
with the reported catalytic systems for the synthesis of 2-substi-
tuted quinoxaline (Table 4). Solid phase synthesis of quinoxaline
using polymer as a support required multistep synthesis and no
data were found on reusability. Although KF-alumina showed
higher yields under solvent-less conditions at room temperature,
it required high catalyst loading (0.5 g) and its reusability was
not reported. In another precedent, b-cyclodextrin was used as cat-
alyst at 70 °C in water but however reusability of catalyst was not
reported. The present catalytic system reports high yield of the
product at moderate reaction temperature (50 °C) in acetonitrile
and it can be reused up to six times which were lacking in the
above examples.
In conclusion, we have developed an efficient one-pot synthesis
of quinoxaline derivatives from substituted o-phenylenediamines
and phenacyl bromides in the presence of K10 clay in acetonitrile
at 50 °C. This methodology allowed us to synthesize a series of
substituted quinoxaline analogues in high yields irrespective of
the kind of functional groups in the starting reagents and above
all the reaction conditions are milder and greener. The other
advantages of this strategy are low cost of catalyst, achieving good
yield of products in high purity, operational simplicity, milder
Run
1st
90
2nd
88
3rd
87
4th
85
5th
83
6th
82
Yieldb (%)
a
Reaction conditions: o-phenyleneamine (1 mmol), phenacyl bromide (1 mmol),
K10 clay (50 mg), acetonitrile (5 mL), 50 °C, 3 h.
b
Isolated yield.
vibration of ammonia coordinatively linked to a Lewis acid centre.
The absorption band in the region at 1445 cmꢀ1 was assigned to
the vibration of the NHþ4 ion indicating the presence of Bronsted
acidic sites.27d
Based on the understanding about the different types of acid
sites in K 10 clay, a tentative mechanism is proposed involving
the reaction of diamine and phenacyl bromide. K10 clay has been
used as solid acid catalysts due to the existence of both Lewis
and Bronsted acid29 sites. In the proposed mechanism, K10 clay
acting as a Bronsted acid polarizes the carbonyl group of phenacyl
bromide giving a carbocationic intermediate as shown in Scheme 1,
subsequent nucleophilic attack by o-phenylenediamine followed
by dehydration gives an imine intermediate II. This is followed
by the SN2 type attack by the second amino group leading to dehy-
drohalogenation and cyclization, giving dihydroquionoxaline III.
Subsequent clay promoted dehydrogenation gives quinoxaline,
Br
N
Ph
O
H+
N
Ph
K10 clay
H2O
oxidation
Br
air
Br
Ph
O
H
N
1 O2
H
H
/
Ph
O
2
H+
H
Ph
N
III
H2
..
NH2
N
H
NH2
..
-HBr
N
H2
H
NH2
..
NH
Br
OH
Ph
..
Br
H
II
N
N
Ph
H2O
Scheme 1. Proposed mechanism for the formation of 2-phenylquinoxaline catalyzed by K10 clay.
Table 4
Comparison of the present catalytic system with the earlier reported procedures for the synthesis of 2-substituted quinoxaline from substituted o-phenylenediamine and
phenacyl bromide
Entry
Catalyst (weight)
Solvent
Temp ( °C)
Time
Yield (%)
Reusability
Ref.
a
a
a
1
2
3
4
5
6
7
Wang resin as polymer support (100 mg)
Perchloric acid supported on silica (50 mg)
Trimethylsilyl chloride (1 mmol)
KF-alumina (0.5 g)
b-Cyclodextrin (1 mmol)
1,4-Diazabicyclo[2,2,2] octane (20 mol %)
K10 clay (50 mg)
—
—
rt
—
78
NR
3b
21b
22a
22b
22c
23
24
Acetonitrile
Water
None
Water
THF
15–60 min
8 h
1.5–5 h
2–2.5 h
20–50 min
3 h
80–95
57–91
82–94
83–92
84–93
83–95
70
rt
70
rt
NR
NR
NR
NR
6(82)
Acetonitrile
50
Present system
a
Required different solvents, temperatures and time due to multistep.
Data were not reported; NR stands for Not Reported.
b

1620
M. Jeganathan et al. / Tetrahedron Letters 55 (2014) 1616–1620
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Acknowledgements
K.P. thanks Department of Science and Technology, New Delhi,
India for the financial assistance. A.D.M. thanks University Grants
Commission, New Delhi for the award of Assistant Professorship
under its Faculty Recharge Program.
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.tetlet.2014.01.
087.
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