A general method for the synthesis of structurally diverse quinoxalines and pyrido-pyrazine derivatives using camphor sulfonic acid as an efficient organo-catalyst at room temperature

Article abstract of DOI:10.1080/00397911.2021.1873383

A mild, convenient, eco-friendly, general and practical approach has been developed for the synthesis of a series of structurally diverse quinoxaline derivatives via the condensation reactions of various 1,2-diaminobenzene derivatives and 1,2-dicarbonyls

Full text of DOI:10.1080/00397911.2021.1873383

Synthetic Communications
An International Journal for Rapid Communication of Synthetic Organic
Chemistry
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A general method for the synthesis of structurally
diverse quinoxalines and pyrido-pyrazine
derivatives using camphor sulfonic acid as an
efficient organo-catalyst at room temperature
Gurpreet Kaur, Arvind Singh, Navdeep Kaur & Bubun Banerjee
To cite this article: Gurpreet Kaur, Arvind Singh, Navdeep Kaur & Bubun Banerjee (2021)
A general method for the synthesis of structurally diverse quinoxalines and pyrido-pyrazine
derivatives using camphor sulfonic acid as an efficient organo-catalyst at room temperature,
Synthetic Communications, 51:7, 1121-1131, DOI: 10.1080/00397911.2021.1873383
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021, VOL. 51, NO. 7, 1121–1131
2
https://doi.org/10.1080/00397911.2021.1873383
A general method for the synthesis of structurally diverse
quinoxalines and pyrido-pyrazine derivatives using
camphor sulfonic acid as an efficient organo-catalyst at
room temperature
Gurpreet Kaur, Arvind Singh, Navdeep Kaur, and Bubun Banerjee
Department of Chemistry, Indus International University, Himachal Pradesh, India
ABSTRACT
ARTICLE HISTORY
A mild, convenient, eco-friendly, general and practical approach has
been developed for the synthesis of a series of structurally diverse
quinoxaline derivatives via the condensation reactions of various
Received 11 October 2020
KEYWORDS
1
,2-diaminobenzene derivatives and 1,2-dicarbonyls such as phenan-
Quinoxalines; pyrido-
pyrazine; camphor sulfonic
acid; room temperature;
organocatalysis
threne-9,10-dione, acenaphthylene-1,2-dione or benzil using a cata-
lytic amount of camphor sulfonic acid as an efficient, commercially
available, low cost, organo-catalyst in aqueous ethanol at room tem-
perature. Under the same optimized conditions we were also
able to synthesis dibenzo[f,h]pyrido[2,3-b]quinoxaline as well as
10-bromoacenaphtho[1,2-b]pyrido[2,3-e]pyrazine from the reactions
of pyridine-2,3-diamines and phenanthrene-9,10-dione or acenaph-
thylene-1,2-dione respectively.
GRAPHICAL ABSTRACT
Introduction
Quinoxaline skeleton is very common in commercially available drug molecules
[
1–6]
(Figure 1).
Many naturally occurring bioactive compounds such as echinomycin,
CONTACT Bubun Banerjee
banerjeebubun@gmail.com, bubun.banerjee@iiuedu.in
Department of Chemistry,
Indus International University, V.P.O. Bathu, Distt. Una, Himachal Pradesh 174301, India.
Supplemental data for this article can be accessed on the publisher’s website.
ß 2021 Taylor & Francis Group, LLC

1
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G. KAUR ET AL.
Figure 1. Drug molecules containing quinoxaline as an important structural subunit.
Figure 2. Glimpse of bioactive synthetic scaffolds containing quinoxaline skeleton.
[
7]
triostin A etc possess quinoxaline as the main structural unit. Various synthetic qui-
noxaline derivatives or quinoxaline fused heterocycles showed potent biological effica-
cies such as anti-inflammatory, anti-bacterial, anti-microbial, anti-dengue, anti-cancer
[
8–13]
etc activities (Figure 2).
After noticing the importance of quinoxaline derivatives, a large number of methods
were reported for the synthesis of structurally diverse quinoxaline derivatives under
[
10,14–28]
various reaction conditions.
Recently, among many others, fused quinoxalines
such as dibenzo[a,c]phenazines or acenaphtho[1,2-b]quinoxalines have also gained con-
siderable attention. Synthesis of dibenzo[a,c]phenazines was accomplished via the reac-
tions of benzene-1,2-diamines and phenanthrene-9,10-dione in the presence of a
number of metal containing homogeneous or heterogeneous catalysts such as
[
29]
[30]
[31]
[32]
CuFe O ,
PbCl2,
MgSO .7H O,
molybdate sulfuric acid,
nano-TiO2,
silica bonded S-sul-
under various reaction condi-
tions. Synthesis of dibenzo[a,c]phenazines required six hours using zeolite-HY as
2
4
4
2
[
33]
[34]
[15]
fonic acid,
tunestate sulfuric acid,
[
35]
catalyst.
nano-Fe O
On the other hand acenaphtho[1,2-b]quinoxalines were synthesized by using
[
4
21]
[36]
as catalysts or by employing ultrasonic irradiation
in water.
3
Therefore, search for a general method for the synthesis of both the scaffolds by avoid-
ing metal containing catalyst under greener conditions still remains a valid exercise.

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Scheme 1. Synthesis of dibenzo[a,c]phenazines, acenaphtho[1,2-b]quinoxalines and 2,3-
diphenylquinoxaline.
Scheme 2. CSA-catalyzed synthesis of dibenzo[f,h]pyrido[2,3-b]quinoxaline (9) and 10-bromoacenaph-
tho[1,2-b]pyrido[2,3-e]pyrazine (10).
In recent years, metal-free organocatalysts have gained tremendous attention due to
[
37–42]
environmental friendliness.
Among many others, camphor sulfonic acid (CSA) has
also drawn significant attention and regarded as an efficient, commercially available,
low cost organocatalyst. Recently, we have reviewed the catalytic efficiency of camphor
[
43]
sulfonic acid for diverse organic transformations.
develop organo-catalyzed protocols
In continuation of our efforts to
[
44–48]
herein we wish to report camphor sulfonic
acid catalyzed a general method for the synthesis of dibenzo[a,c]phenazines, acenaph-
tho[1,2-b]quinoxalines, 2,3-diphenylquinoxaline and pyrido-pyrazine derivatives in
aqueous ethanol at room temperature (Schemes 1 & 2).

1
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G. KAUR ET AL.
Table 1. Optimization of reaction conditions for the synthesis of dibenzo[a,c]phenazines.
a,b
Entry
Catalyst (mol%)
Catalyst-free
Catalyst-free
Condition
neat
EtOH
H O
2
EtOH
Time (h)
Yield (%)
1
2
3
4
5
6
7
8
9
1
1
1
1
1
a
.
6
6
2
2
2
2
2
2
2
2
2
1
1
1
0
trace
42
56
52
32
78
68
49
44
82
92
81
93
Mandelic acid (20)
Mandelic acid (20)
Mandelic acid (20)
Mandelic acid (20)
Mandelic acid (20)
Itaconic acid (20)
Palmitic acid (20)
Shikimic acid (20)
Acetic acid (two drops)
CSA (20)
MeOH
MeCN
H
H
H
H
H
H
H
H
2
O:EtOH
2
O:EtOH
2
O:EtOH
2
O:EtOH
2
O:EtOH
2
O:EtOH
2
O:EtOH
2
O:EtOH
0
1
2
3
4
CSA (15)
CSA (25)
Reaction conditions: o-phenylenediamine (1; 1 mmol) and phenanthrene-9,10-dione (2; 1 mmol) in the absence or pres-
ꢀ
b
ence of catalyst in neat/4 mL of water/ethanol/aqueous ethanol at 28–32 C. Isolated yields.
Results and discussion
During optimization, we carried out a number of trial reactions between o-phenylenedi-
amine (1a; 0.5 mmol) and phenanthrene-9,10-dione (2; 0.5 mmol) under various reac-
tion conditions at room temperature. Initially, we performed the reaction in absence of
any catalyst under neat conditions at room temperature which failed to produce even
trace amount of the desired product after 6 hours (Table 1, entry 1). It may be due to
poor miscibility as both the reactants are solid at room temperature. Under catalyst-free
conditions the same reaction afforded trace amount of yield in ethanol as a solvent after
6
hours (Table 1, entry 2). After noticing the poor results under catalyst-free conditions
we realized that a catalyst is required to promote the reaction. In continuation of our
[
46–48]
efforts with mandelic acid as catalyst,
initially we were interested to check the
catalytic efficiency of mandelic acid for this reaction also. For that, we carried out the
same reaction by employing 20 mol% mandelic acid as catalyst in water as solvent which
afforded only 42% of the corresponding dibenzo[a,c]phenazine (3a) after two hours
(Table 1, entry 3). Using mandelic acid as catalyst, the same reaction in ethanol yielded
56% of 3a after two hours (Table 1, entry 4). By using methanol (Table 1, entry 5) or
acetonitrile (Table 1, entry 6) as solvent the corresponding yields were 52% or 32%
respectively. Yield was increased (78%) when the same reaction carried out in aqueous-
ethanol (1:1 v/v) though time required still two hours (Table 1, entry 7). From these ini-
tial studies it was established that aqueous-ethanol is the best suitable solvent to carry
out this reaction under greener condition. But we were not satisfied with the catalytic
performance of mandelic acid that’s why we interested to reinvestigate the catalytic effi-
ciency by employing some other metal-free organo-catalysts. As a result, for this reac-
tion we used 20 mol% of itaconic acid (Table 1, entry 8), palmitic acid (Table 1, entry

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9
) and shikimic acid (Table 1, entry 10) as catalysts in aqueous-ethanol as solvent.
Itaconic acid produced 68% yield of compound 3a whereas palmitic acid and shikimic
acid afforded below fifty percent yield after two hours. With two drops acetic acid as
catalyst the same reaction in aqueous ethanol afforded the desired product with 82%
yield after two hours (Table 1, entry 11). Surprisingly, when we employed 20 mol%
camphor sulfonic acid (CSA) as catalyst in aqueous ethanol, the reaction completed
within just one hour and produced 92% yield of the desired product (Table 1, entry
1
2). We tried to standardize the required catalyst amount maintaining other parameters
remain same. Lesser amount of product (81%) was isolated using 15 mol% of CSA
Table 1, entry 13). There was no significant improvement in the reaction rate even
(
after increasing the catalyst amount to 25 mol% (Table 1, entry 14). Therefore, it was
came out that 20 mol% of camphor sulfonic acid (CSA) is an efficient organo-catalyst
for the synthesis of dibenzo[a,c]phenazine (3a) from the reaction of o-phenylenediamine
(1a) and phenanthrene-9,10-dione (2) in aqueous ethanol at room temperature. Under
the same optimized reaction conditions, we were successfully synthesized 10-methyldi-
benzo[a,c]phenazine (3b) with excellent yields (87) within one hour from the reactions
of 3-methylbenzene-1,2-diamine (1b) with phenanthrene-9,10-dione (2) (Table 2, entry
2). To establish the effectiveness of our optimized reaction conditions, we then carried
out the reactions of benzene-1,2-diamines (1a–1d, 0.5 mmol) with acenaphthylene-1,2-
dione (4, 0.5 mmol) instead of phenanthrene-9,10-dione (2, 0.5 mmol) under the same
reaction conditions which afforded the corresponding acenaphtho[1,2-b]quinoxalines
(5a–5d) with excellent yields (82–96%) within 45 minutes (Table 2, entries 3–6).
Moreover, synthesis of 2,3-diphenylquinoxaline (7) was also achieved with 92% yield
under the same optimized conditions from the reaction of o-phenylenediamine (1a) and
benzil (6) (Table 2, entry 7). To extend the scope of our developed protocol, we were
then motivated to carry out the same batch of reactions with pyridine-2,3-diamines
(8a,8b) instead of o-phenylenediamine (1a). It is our delight to mention that under
the same optimized reaction conditions we were also able to synthesize
dibenzo[f,h]pyrido[2,3-b]quinoxaline (9) (Table 2, entry 8) and 10-bromoacenaph-
tho[1,2-b]pyrido[2,3-e]pyrazine (10) (Table 2, entry 9) starting from pyridine-2,3-dia-
mines (8a,8b) and phenanthrene-9,10-dione (2) or acenaphthylene-1,2-dione (4)
respectively.
All the synthesized compounds were isolated pure just by simple filtration and subse-
quent washing with aqueous ethanol; no column chromatographic purification was
required. Gram scale production of dibenzo[a,c]phenazine (3a) was also achieved within
three hours from the reactions of 10 mmol o-phenylenediamine (1a) and 10 mmol phen-
anthrene-9,10-dione (2) using 20 mol% CSA in aqueous ethanol at room temperature.
All the compounds synthesized were well characterized by the detail spectroscopic anal-
1
13
yses of H NMR, C NMR and HRMS.
Experimental section
General
Melting points were recorded on a Digital Melting Point Apparatus (Model No. MT-
1
9
34) and are uncorrected. TLC was performed on silica gel 60 F254 (Merck) plates. H

1
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G. KAUR ET AL.
Table 2. Synthesis of dibenzo[a,c]phenazine (3a–3b), acenaphtho[1,2-b]quinoxalines (5a–5d), 2,3-
diphenylquinoxaline (7), dibenzo[f,h]pyrido[2,3-b]quinoxaline (9) and 10-bromoacenaphtho[1,2-b]pyr-
ido[2,3-e]pyrazine (10) using camphor sulfonic acid as catalyst at room temperature.
Entry 1,2-diamines
1,2-
Product
Time (h)
Yield (%)a,b
dicarbonyls
1
1
92
2
3
1
87
94
0.75
4
5
0.75
0.75
96
89
6
7
8
0.75
0.75
1.5
82
92
72
9
1.5
76
a
Reaction conditions: o-phenylenediamines (1a–1d; 0.5 mmol) or pyridine-2,3-diamines (8a–8b; 0.5 mmol) and phenan-
threne-9,10-dione (2; 0.5 mmol) or acenaphthylene-1,2-dione (4; 0.5 mmol) or benzil (6; 0.5 mmol) in the presence of
2
ꢀ
0 mol% camphor sulfonic acid (0.023 g) as catalyst in aqueous ethanol at 28–32 C. Isolated yields.
b
1
3
and C NMR spectra were obtained at 500 MHz Jeol (JNM ECX-500) NMR machines

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þ
with CDCl as the solvent. Mass spectra (TOF-MS ES ) were measured on a Bruker
3
Impact HD QTOF Micro mass spectrometer.
Synthesis of dibenzo[a,c]phenazine (3a)
In an oven dried clean reaction tube o-phenylenediamine (1; 0.5 mmol), phenanthrene-
9,10-dione (2; 0.5 mmol) and a catalytic amount of camphor sulfonic acid (20 mol%)
were taken sequentially. The reaction mixture was then stirred vigorously in aqueous
ethanol as solvent at room temperature. Progress of the reaction was monitored by
TLC. After completion of the reaction, synthesized dibenzo[a,c]phenazine (3a) was iso-
lated pure with 92% yield just by simple filtration and subsequent washing with aqueous
ethanol (EtOH:H O ¼ 1:1). The structure of the synthesized compound was determined
2
1
13
by the detail spectral analysis including H NMR, C NMR and HRMS spectroscopy.
ꢀ
Dibenzo[a,c]phenazine (3a): White solid; yield 92%; mp 228–230 C (lit.
ꢀ
[29] 1
2
29–231 C) ; H NMR (500 MHz, CDCl ) d/ppm: 9.39 (2H, dd, J ¼ 8.3 & 1.5 Hz, aro-
3
matic H), 8.55 (2H, d, J ¼ 8.0 Hz, aromatic H), 8.33–8.31 (2H, m, aromatic H),
.85–7.84 (2H, m, aromatic H), 7.79 (2H, td, J ¼ 8.0 & 1.5 Hz, aromatic H), 7.74 (2H,
7
1
3
td, J ¼ 8.0 & 1.5 Hz, aromatic H); C NMR (125 MHz, CDCl ) d/ppm: 142.5 (2 C),
3
1
1
2
42.3 (2 C), 132.1 (2 C), 130.4 (2 C), 130.3 (2 C), 129.9 (2 C), 129.5 (2 C), 128.0 (2 C),
26.3 (2 C), 123.0 (2 C); HRMS (ESI-TOF) m/z: For C H N Calcd. [M þ H]þ
20
12 2
þ
81.1079; Found [M þ H] 281.1356.
Synthesis of acenaphtho[1,2-b]quinoxaline (5a)
By repeating the above mentioned procedure, acenaphtho[1,2-b]quinoxaline (5a) was
also synthesized from the reactions of o-phenylenediamine (1; 0.5 mmol) and acenaph-
thylene-1,2-dione (4; 0.5 mmol) by using camphor sulfonic acid as catalyst under the
same optimized conditions.
ꢀ
Acenaphtho[1,2-b]quinoxaline (5a): White solid; yield 94%; mp 232–234 C (lit.
ꢀ
[29] 1
2
28–230 C) ; H NMR (500 MHz, CDCl ) d/ppm: 8.42 (2H, d, J ¼ 7.0 Hz, aromatic
3
H), 8.22–8.20 (2H, m, aromatic H), 8.10 (2H, d, J ¼ 8.0 Hz, aromatic H), 7.84 (2H, t,
13
J ¼ 7.5, aromatic H), 7.77–7.75 (2H, m, aromatic H); C NMR (125 MHz, CDCl )
3
d/ppm: 154.2 (2 C), 141.4 (2 C), 136.6, 131.9 (2 C), 130.1, 129.7 (2 C), 129.6 (2 C), 129.3
þ
(
2
2 C), 128.8 (2 C), 121.9 (2 C); HRMS (ESI-TOF) m/z: For C H N Calcd. [M þ H]
18
10 2
þ
55.0922; Found [M þ H] 255.0734.
Supporting information
1
13
Full experimental detail, scanned spectra including H-NMR, C-NMR and HRMS of
all the synthesized scaffolds are supplemented in supporting information. This material
can be found via the “Supplementary Content” section of this article’s webpage.’
Conclusions
In conclusion, we have developed a simple and facile method for the synthesis of a
series of structurally diverse quinoxaline derivatives via the condensation reactions of
various 1,2-diaminobenzene derivatives and 1,2-dicarbonyls such as phenanthrene-9,10-

1
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G. KAUR ET AL.
dione, acenaphthylene-1,2-dione or benzil using a catalytic amount of camphor sulfonic
acid as a commercially available metal-free organo-catalyst in aqueous ethanol at
room temperature. Synthesis of dibenzo[f,h]pyrido[2,3-b]quinoxaline as well as 10-bro-
moacenaphtho[1,2-b]pyrido[2,3-e]pyrazine was also accomplished from the reactions of
pyridine-2,3-diamines and phenanthrene-9,10-dione or acenaphthylene-1,2-dione
respectively under the same optimized reaction conditions. Mild reaction conditions,
use of metal-free organocatalyst, high yields, short reaction times, column-free purifica-
tion procedure are some of the major advantages of this developed protocol.
Acknowledgements
Dr. B. Banerjee is thankful to the Indus International University, Una, Himachal Pradesh, India
and the Kartha Education Society, Mumbai, India for the support. Authors are grateful to
1
13
AMRC, IIT Mandi, Himachal Pradesh, India for the spectral measurements such as H and
C
NMR and HRMS data.
Disclosure statement
No potential conflict of interest was reported by the author(s).
ORCID
Bubun Banerjee
http://orcid.org/0000-0001-7119-9377
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