Polyethylene glycol in water: A simple, efficient and green protocol for the synthesis of quinoxalines

Article abstract of DOI:10.1007/s12039-011-0081-8

A variety of biologically important quinoxaline derivatives has been efficiently synthesized in excellent yields under extremely mild conditions using PEG-600 and water. This inexpensive, non-toxic, ecofriendly and readily available system efficiently condensed several aromatic as well as aliphatic 1,2-diketones with aromatic and aliphatic 1,2-diamines to afford the products in excellent yield. Polyethylene glycol (PEG) can be recovered and recycled. Indian Academy of Sciences.

Full text of DOI:10.1007/s12039-011-0081-8

c
J. Chem. Sci. Vol. 123, No. 4, July 2011, pp. 477–483. ꢀ Indian Academy of Sciences.
Polyethylene glycol in water: A simple, efficient and green protocol for
the synthesis of quinoxalines
HEMANT V CHAVAN, LAXMAN K ADSUL and BABASAHEB P BANDGAR∗
Medicinal Chemistry Research Laboratory, School of Chemical Sciences, Solapur University,
Solapur 413 255, (MS) India
e-mail: bandgar_bp@yahoo.com
MS received 7 October 2010; accepted 28 February 2011
Abstract. A variety of biologically important quinoxaline derivatives has been efficiently synthesized in
excellent yields under extremely mild conditions using PEG-600 and water. This inexpensive, non-toxic, eco-
friendly and readily available system efficiently condensed several aromatic as well as aliphatic 1,2-diketones
with aromatic and aliphatic 1,2-diamines to afford the products in excellent yield. Polyethylene glycol (PEG)
can be recovered and recycled.
Keywords. Polyethylene glycol (PEG); water; 1,2-dicarbonyls; 1,2-diamines; recyclability; quinoxalines.
1. Introduction
in refluxing ethanol or acetic acid.13 Apart from
this, other methods such as solid phase synthe-
sis,14 oxidative cyclisation of α-hydroxy ketones with
1,2–diamines,15 cyclisation-oxidation of phenacyl bro-
mides with 1,2-diamines by HClO4-SiO2,16 cyclisation
of o-phenylenediamine with propiophenone by using
KOH,17 and oxidative coupling of epoxides with ene-
1,2-diamines18 have also been reported. Nevertheless,
most of the methods suffer from several drawbacks such
as critical product isolation, expensive metal catalyst,
harsh reaction conditions, and use of strong oxidizing
agents, long reaction time and low yields. Therefore,
the development of simple, more efficient and environ-
mentally benign method is useful in generating organic
compounds in drug discovery process.
Quinoxaline derivatives are important class of nitrogen-
containing heterocycles, having interesting therapeutic
properties such as antiviral, antibacterial, antibiotic,
antiinflammatory and kinase inhibition.1 They have al-
so been evaluated as anticancer, antimycobacterial, and
anthelmintic agents.2 Besides this, they are potential
building blocks for the synthesis of anion receptors,3
cavitands,4 dehydroannulenes,5 organic semiconductors,6
and dyes.7 Molecules like dipyrido[3,2-a:2’,3’-c]
phenazine (dppz),8 dipyrido[3,2-f:2’,3’-h]quinoxaline
(dpq)9 and tetrapyrido[3,2-a:2’,3’-c:3”,2”-h:2”’,3”’-
j]phenazine (tpphz)10 derivatives exhibit interesting
properties, such as bidentate coordination ability, rigid-
ity, π-accepting character and planar highly conjugated
aromatic structure (figure 1). All these interesting
properties and nitrogen sites enable them to act as ther-
apeutic agents that are capable of binding and cleaving
An increase in regulatory restrictions on the use,
manufacture and disposal of organic solvents has
focused attention on the development of non-hazardous
alternatives for the sustainable development of chemi-
DNA under the physiological condition.11 In addition, cal enterprise. Liquid polymers have been used as green
organometallic complexes of these ligands show inter- reaction media with unique properties such as ther-
esting optical, electrochemical and electroluminescent mal stability, commercial availability, non-volatility,
properties.12
immiscibility with organic solvents and recyclability.
Recently, polyethylene glycol (PEG) and its aqueous
solutions represent interesting solvent systems for sol-
vent replacement, and may stand comparison to other
currently favoured systems such as ionic liquids, super-
critical carbon dioxide, and micellar systems.19 PEGs
are selected instead of other polymers because they
are inexpensive, biodegradable, non-halogenated and
having low toxicity.
A number of methods have been developed for
the synthesis of substituted quinoxaline derivatives
and the most common method is the condensation of
an aryl 1,2-diamine with 1,2-dicarbonyl compounds
∗For correspondence
477

478
Hemant V Chavan et al.
N
N
N
N
N
N
N
N
N
N
N
N
N
N
dpq
dppz
tpphz
Figure 1. Representatives of quinoxaline ring containing compounds.
2.2b 2,3-Bis-(4-fluoro-phenyl)-quinoxaline (3b): Co-
lourless solid; yield 96%; mp 104◦C; IR (KBr): 3074,
N
N
H2N
H2N
O
O
1
3061, 1664, 1599, 1512 cm−1; H NMR (400 MHz,
PEG-600-H20
RT, 3 min
+
DMSO-d6): δ 7.24 (m, 4H), 7.52 (m, 2H), 7.90 (m,
2H), 8.05 (m, 2H), 8.20 (m, 2H); 13C NMR (100 MHz,
CDCl3): δ 128.4, 129.2, 130.1, 132.6, 133.4, 144.2,
155.1; MS (ESI): m/z319 (M+H)+.
1
2
3a
Scheme 1. Synthesis of quinoxaline.
2.2c Dipyrido[3,2-a:2’,3’-c]phenazine (dppz) (3c):
Light brown; yield 95%; mp 246◦C; IR (KBr):
As a part of ongoing program on the development
of novel methods in organic synthesis,20 we report here
a simple, efficient and green protocol for the synthe-
sis of quinoxalines. In this protocol, 1,2-diketone 1 and
1,2-diamine 2 in PEG-H2O after stirring at room tem-
perature for specified time resulted in the formation of
product 3a in 98% yield (scheme 1).
1
3079, 3052, 3025, 1590, 1492, 1081 cm−1; H NMR
(400 MHz, DMSO-d6): δ = 9.68 (dd, J = 8.2, 1.3 Hz,
2H); 7.95 (dd, J =8.2, 5.4 Hz, 2H); 8.30 (dd, J =5.4,
1.3 Hz, 2H); 8.42 (d, J = 8.0 Hz; 2H); 8.14 (d, J =
8.0 Hz, 2H); 13C NMR (100 MHz, CDCl3): δ 125.8,
129.6, 130.2, 130.8, 131.1, 138.4, 144.6, 147.8, 153.2;
MS (ESI): m/z 283 (M+H)+.
2. Experimental
2.2d Dibenzo[a,c]phenazine (3d): Yellow solid;
yield 97%; mp 218◦C; IR (KBr): 3059, 3032, 1604,
2.1 General procedure for the synthesis of
quinoxalines
1
1500 cm−1; H NMR (400 MHz, DMSO-d6): δ = 7.82
(m, 2H), 7.90 (m, 2H), 8.00 (m, 2H), 8.35 (m, 2H),
8.80 (d, J = 8 Hz, 2H), 9.28 (d, J = 8 Hz, 2H); 13C
NMR (100 MHz, CDCl3): δ 126.2, 127.1, 127.6, 128.1,
129.8, 130.7, 132.4, 135.9, 142.6, 151.2; MS (ESI):
m/z 281 (M+H)+.
A mixture containing 1,2-dicarbonyl compound 1
(1 mmol) and 1,2-diamine 2 (1 mmol) in PEG-600-H2O
(1:1, 5 ml) was stirred at room temperature for the
specified time. After completion of the reaction (TLC),
water (10 ml) was added to the reaction mixture. Pre-
cipitate obtained was filtered, washed with water and
dried to obtain quinoxaline 3 in almost pure form. All
2.2e 2,3-Difuran-2-yl-quinoxaline (3e): Pale brown
solid; yield 97%; mp 130◦C; IR (KBr): 3107, 3061,
1
the products were characterized by IR, H NMR, 13C
1
1572, 1529, 1400 cm−1; H NMR (400 MHz, DMSO-
NMR, and Mass Spectroscopy.
d6): δ = 6.72 (s, 4H), 7.90 (m, 4H), 8.10 (m, 2H); 13C
NMR (100 MHz, CDCl3): δ 120.1, 129.8, 132.2, 144.6,
146.5, 148.4, 156.9; MS (ESI): m/z263 (M+H)+.
2.2 Spectral data of some representative compounds
2.2a 2,3-Diphenyl-quinoxaline (3a): White solid;
yield 98%; mp 126◦C; IR (KBr): 3056, 1964, 1577,
2.2f 2,3-Diphenylpyrido[2,3-b]pyrazine (3g): Yel-
1
1556, 1540, 1495 cm−1; H NMR (400 MHz, DMSO-
low solid, yield 94%; mp 257◦C; IR (KBr): 1588, 1545,
d6): δ 7.35 (m, 6H), 7.50 (m, 4H), 7.90 (dd, J = 8, 2 Hz,
2H), 8.20 (d, J = 8, 2 Hz, 2H); 13C NMR (100 MHz,
CDCl3): δ 128.2, 128.8, 129.2, 129.8, 129.9, 139.1,
141.2, 153.5; MS (ESI): m/z 283 (M+H)+.
1
1430, 1382, 1328 cm−1; H NMR (400 MHz, DMSO-
d6): δ = 7.31–7.41 (m, 6H), 7.56 (d, J = 7.8 Hz, 2H),
7.64 (d, J =7.8 Hz, 2H), 7.74–7.76 (dd, J = 8.4, 4.1 Hz,
1H), 8.55–8.57 (d, J =8.2 Hz, 1H), 9.19 (d, J =4.2 Hz,

Polyethylene glycol in water: a simple, efficient and green protocol for the synthesis of quinoxalines
479
N
N
O
O
H2N
H2N
N
N
N
N
N
N
N
N
PEG-600-H2O
RT, 30 min
+
4
5
6
Scheme 2. Synthesis of tetrapyrido[3,2-a:2’,3’-c:3”,2”-h:2”’,3”’-j]phenazine (tpphz).
1H); 13C NMR (100 MHz, CDCl3): δ 125.2, 128.2, 2.2j Tetrapyrido[3,2-a:2’,3’-c:3”,2”-h:2”’,3”’-j]phe-
128.5, 129.4, 129.6, 129.8, 130.3, 136.2, 138.0, 138.5, nazine (tpphz) (scheme 2, compound 6): Yellow solid;
149.4, 153.6, 155.0, 156.6; MS (ESI): m/z 283 (M+).
Yield 73%; mp > 295◦C; IR (KBr): 3082, 3061, 3026,
1
1595, 1496, 1082 cm−1; H NMR (400 MHz, CDCl3):
δ = 7.92 (dd, J = 8.4, 5.2 Hz, 4H); 9.40 (dd, J = 5.2,
1.7 Hz, 4H); 9.87 (dd, J = 8.4, 1.7 Hz, 4H); 13C NMR
(100 MHz, CDCl3): δ 125.2, 130.6, 131.1, 138.5 146.8,
155.4; MS (ESI): m/z 385 (M+H)+
2.2g 5,6-Diphenyl-2,3-dihydro-pyrazine (3l): White
solid; yield 94%; mp 156◦C; IR (KBr): 3081, 2943,
2832, 1964, 1896, 1610, 1572 cm−1; 1H NMR (DMSO-
d6): δ = 3.60 (s, 4H), 7.30 (m, 10H); 13C NMR
(100 MHz, CDCl3): δ 52.4, 128.2, 129.4, 130.8, 136.8,
161.6; MS (ESI): m/z 235 (M+H)+.
3. Results and discussion
In the beginning, a reaction of benzil and o-
phenylenediamine in water was carried out at room
temperature, which resulted in the formation of a con-
densation product 3a after 6 hours (59%). With sim-
ilar substrates, reaction was carried out in PEG-600
afforded the title compound 3a in 20 min (83% yield).
Inspired by these results, we introduced PEG–H2O as a
solvent system and found that the reaction rate was sig-
nificantly improved. By changing proportion of PEG–
H2O, dramatic effect on the conversion rate of quinox-
aline has been observed (table 1). As shown in table 1,
when pure PEG was used as a solvent, the reaction
was completed in 20 min. However, addition of water
to PEG increased the rate of the reaction as well as
yield of the product (table 1, entries 2, 3). When the
proportion of PEG–H2O was 1:1, the highest reaction
rate was observed (table 1, entry 3). On the other hand,
2.2h 1,2,3,4-Tetrahydro-phenazine (3m): white so-
lid, yield 90%, mp 178◦C, IR (KBr): 1459, 1423, 1384,
1
1330, 1291, 1238 cm−1; H NMR (400 MHz, CDCl3)δ
= 2.04 (m, 4H), 3.16 (m, 4H), 7.65 (m, 2H), 7.97 (m,
2H); 13C NMR (100 MHz, CDCl3): δ 22.8, 33.2, 128.3,
128.9, 141.2, 154.1; MS (ESI): m/z 184 (M+).
2.2i 2,3,2’,3’-Tetraphenyl-[6,6’] biquinoxalinyl (3q):
Yellow solid; yield 89%; mp > 295◦C; IR (KBr): 3084,
1
3055, 3032, 1612, 1599 cm−1; H NMR (DMSO-d6):
δ = 7.35 (m, 12H), 7.55 (d, J = 8.1 Hz, 8H), 8.23 (d, J
= 8.5 Hz, 2H), 8.32 (d, J = 8.5 Hz, 2H), 8.60 (s, 2H);
13C NMR (100 MHz, CDCl3): δ 155.8, 154.2, 142.1,
141.7, 141.3, 140.0, 131.1, 130.8, 130.5, 130.1, 129.0,
128.3; MS (ESI): m/z 563 (M+H)+.
Table 1. Effect of the PEG-600 to H2O volume ratio on
quinoxaline synthesis.
Table 2. Optimisation of reaction conditions using differ-
ent PEG–H2O systems.
Entry PEG (ml) H2O (ml) Time (min/hr) Yield (%)a
Entry
Solventa
Time (min)
Yield (%)b
1
2
3
4
5
5
4
2.5
1
0
1
2.5
4
20 min
15 min
3 min
1.5 hr
6 hr
83
89
98
82
59
1
2
3
4
5
PEG-200-H2O
PEG-300-H2O
PEG-400-H2O
PEG-600-H2O
PEG-800-H2O
12
8
5
3
5
87
94
97
98
96
0
5
Reaction conditions: Benzil (1 mmol), o-phenylenediamine
(1 mmol), PEG–H2O, RT
aPEG-H2O volume ratio: (1:1). bIsolated yields after
purification
aIsolated yields after purification

480
Hemant V Chavan et al.
Table 3. Synthesis of quinoxaline using different aromatic, heterocyclic and aliphatic 1,2-diketones.
a
Entry
Dicarbonyls
Diamines
Product
Time
(min)
Yield (%)b
3a
O
O
N
N
H2N
H2N
3
2
98c
F
F
F
3b
H2N
H2N
O
O
N
N
96
F
3c
3d
3e
N
N
O
N
N
N
N
H2N
H2N
3
5
95
97
O
O
O
N
N
H2N
H2N
O
O
N
N
H2N
H2N
O
O
O
O
5
5
97
92
O
3f
N
H2N
H2N
O
N
N
N
H
H
3g
O
O
N
N
H2N
5
5
94
90
N
N
N
H2N
N
N
3h
N
N
O
O
N
N
N
N
H2N
H2N
3i
3j
N
N
O
O
H2N
H2N
5
3
94
95
N
N
F
F
F
F
H2N
H2N
O
N
N
O
N

Polyethylene glycol in water: a simple, efficient and green protocol for the synthesis of quinoxalines
Table 3. (continued).
481
b
Entry
Dicarbonyls
Diamines
Product
Time
(min)
Yield (%)
O
O
N
N
H2N
O
O
3k
O
O
5
2
95
N
H2N
N
O
O
N
N
H2N
H2N
3l
94
O
O
H2N
N
N
3m
3n
3o
5
2
5
5
90
92
89
85
H2N
O
O
H2N
H2N
N
N
O
O
H2N
H2N
N
N
O
O
H2N
H2N
N
N
3p
Ph
Ph
NH2
N
NH2
N
O
O
5
89
3q
N
H2N
N
NH2
Ph
Ph
a
Reaction conditions: PEG-600-H2O. All products were characterised by IR,1H NMR,13C NMR and MS.
c
bIsolated yields after purification. PEG was recovered and reused for three consecutive runs
further addition of water resulted in decrease reac- from PEG-200 to PEG-600 and decreased when the
tion rate due to decreased solubility of substrates in molecular weight was over 600. This could be attributed
PEG–H2O. In summary, to obtain high reactivity within to the lower viscosity and better hydrophilic charac-
a short period of time, an optimum volume ratio of ter but the low solubility of the substrates in PEG
PEG to H2O was necessary, for example, 1:1 during with low molecular weight. When PEGs with molec-
quinoxaline synthesis.
ular weight over 600 were used, decreased rate of
We have also studied the effect of PEG with dif- reaction was observed due to higher viscosity of the
ferent molecular weights on the rate of quinoxaline reaction medium. As a result of the above studied
formation. The rate of conversion increased continu- parameters, PEG-600-H2O (1:1) system, found to be
ously with the increase in the molecular weight of PEG effective for the synthesis of quinoxalines at room

482
Hemant V Chavan et al.
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4. Conclusion
In conclusion, we have developed a novel, efficient and
eco-friendly method for the synthesis of quinoxalines
from various 1,2-diketones and 1,2-diamines using
PEG–H2O as a new reaction medium. This medium
rendered this procedure attractive and environmentally
benign. In addition to its efficiency and simplicity,
this method provided high yields of biologically potent
quinoxalines in short reaction time.
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Junior Research Fellowship.

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