One-pot synthesis of quinoxaline-2-carboxylate derivatives using ionic liquid as reusable reaction media

Article abstract of DOI:10.1016/j.tetlet.2010.05.099

The catalyst-free one-pot synthesis of quinoxaline-2-carboxylate is reported by the reaction of α-halo-β-ketoesters with 1,2-diamines using an ionic liquid as an environmentally benign solvent. The recovered ionic liquid was reused for four to five cycles

Full text of DOI:10.1016/j.tetlet.2010.05.099

Tetrahedron Letters 51 (2010) 4313–4316
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Tetrahedron Letters
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One-pot synthesis of quinoxaline-2-carboxylate derivatives using ionic liquid
as reusable reaction media
*
H. M. Meshram , P. Ramesh, G. Santosh Kumar, B. Chennakesava Reddy
Organic chemistry Division-I, Indian Institute of Chemical Technology, Hyderabad 500 007, India
a r t i c l e i n f o
a b s t r a c t
Article history:
The catalyst-free one-pot synthesis of quinoxaline-2-carboxylate is reported by the reaction of a-halo-b-
ketoesters with 1,2-diamines using an ionic liquid as an environmentally benign solvent. The recovered
ionic liquid was reused for four to five cycles. Moreover, the method is applicable for a variety of 1,2-dia-
mines and a-halo-b-ketoesters.
Received 6 April 2010
Revised 19 May 2010
Accepted 22 May 2010
Available online 2 June 2010
Ó 2010 Elsevier Ltd. All rights reserved.
Keywords:
1,2-Diamines
Ionic liquids (ILs)
Quinoxalines
a-Halo-b-ketoesters
Quinoxaline moiety is found in biologically active natural prod-
some of the methods have drawbacks such as unsatisfactory yields,
expensive and detrimental metal reagents. In view of this, there is
still a need to develop a general, efficient and catalyst-free method
for the synthesis of more functionalized quinoxaline derivatives.
Recently, ionic liquids have received much attention due to
their unique properties such as non-volatility, non-flammability,
reusability and great potential as environmentally benign media.13
Some of the ionic liquids have been proved to act as catalysts
because of their high polarity and the ability to solubilize both
inorganic and organic compounds, which can result in the
enhancement of the rate of the reaction. 1-Butyl-3-methylimidazo-
lium tetrafluoroborate [bmim]BF4 (Fig. 1) has gained more popu-
larity and is used in various organic transformations such as
vicinal diamines,14 one-pot syntheses of 2H-indazolo[2,1-b]-
phthalazine-triones15 and hydrative cyclization of 1,6-diynes.16 In
continuation of our work in the development of green methodolo-
gies17 and particularly in the development of non-metallic re-
agents18, herein we wish to report an efficient and mild synthesis
ucts, in many pharmaceuticals as well as in agrochemicals.1 Some
of the quinoxaline derivatives are found to exhibit a broad spec-
trum of biological activity.1c Many quinoxaline derivatives have a
wide application in dyes,2a as an efficient electroluminescent
material,2b as organic semiconductors,2c as dehydroannulenes2d
and in chemically controllable switches.2e The quinoxaline ring is
also found in antibiotics such as echinomycin, leromycin and acti-
nomycin.3 Due to the distinguished biological and physical proper-
ties of quinoxalines, there has been a tremendous interest to devise
a simple and efficient method for the synthesis of more functional-
ized quinoxaline derivatives.
Commonly, a practicable method comprises the reaction of con-
densation of aryl 1,2-diamines with 1,2-dicarbonyl compounds,4
1,4-addition of 1,2-diamines to diazenylbutens5 and oxidation-
trapping of a
-hydroxy ketones with 1,2-diamines.6 Other reported
methods accomplished the synthesis of quinoxalines by the reaction
of 1,2-diamines with phenacyl bromides in solid-phase7 or using
8
heterogeneous catalyst such as HClO4–SiO2 and b-cyclodextrin
of quinoxalines from a-halo-b-ketoesters using ionic liquid as a
(b-CD).9 In addition to this,
a
-ketoesters,10 3-{[(tert-butoxy)car-
reaction medium in the absence of catalyst. To the best of our knowl-
edge this is the first report for the one-pot synthesis of functional-
ized quinoxalines.
bonyl]diazenyl}but-2-enoats11 and N@N polymer-bound 1,2-dia-
za-1,3-butadiene12 have been reported for the synthesis of
quinoxaline. Moreover, the attempted reaction of
a
-halo-b-ketoest-
Thus, the reaction of 1,2-phenylenediamine with
ketoesters in ionic liquid [bmim]BF4 at rt gave the expected quin-
a-halo-b-
ers with 1,2-diamines also reported to give an uncyclized product.11
Although the reported methods provide good isolated yields,
these methods suffer from tedious work-up, longer reaction time,
use of metal catalyst and narrow scope of substrates. Moreover,
N
N
⊕
BF4
* Corresponding author. Tel.: +91 40 27160123 2642; fax: +91 40 27160512.
E-mail address: hmmeshram@yahoo.com (H.M. Meshram).
Figure 1. Chemical structure of representative ionic liquid (IL).
0040-4039/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2010.05.099

4314
H. M. Meshram et al. / Tetrahedron Letters 51 (2010) 4313–4316
R2
NH2
N
O
R
ref. 12
OR1
R3
O
O
H2N
H2N
R2
R3
X
uncyclised product
R
OR1
+
O
X
1
R2
2
N
R2 = H,CH3, COOMe, NO
OR1
[Bmim]BF4
rt
R = CH3, Ph, CF3, isopropyle
R1 = Me, Et, Bn
2
R3 = H,CH3
R3
N
R
X = Cl, Br
3
Scheme 1.
vents such as CH2Cl2, THF and CH3CN. Though the reaction of 1,2-
diamine and
-halo-b-ketoester is reported11 to give an uncyclized
a
product. The same reaction was forced to give the expected cy-
clized product in the present reaction conditions. This fact clearly
indicated that in the present reaction, the ionic liquid plays the
dual role of solvent and promoter19 (Fig. 2). The reaction in ionic
liquid is more advantageous, because ionic liquid can be recycled
and reused in subsequent reactions. After the separation of the
product by extraction of ionic liquid, it was thoroughly washed
with ether and activated at 80 °C under reduced pressure. The reac-
tivated ionic liquid was used for three cycles without any substan-
tial loss in activity, while the reactivity gradually decreased for the
next few cycles. For example, the reaction of 1,2-phenylenedi-
H2N
NH2
R
O
COOR1
Br
Q+ X
Q+X- = [Bmim] BF4
amine with a-halo-b-ketoesters in ionic liquid [bmim]BF4 afforded
Figure 2. Plausible mechanistic pathway.
93%, 92%, 92%, 85% and 80%, respectively, over five cycles. Encour-
aged by these results, we have extended this procedure20 for differ-
oxalines in high yield (93%) (Scheme 1). The reaction proceeded
readily at rt and after work-up, the quinoxaline was the sole prod-
uct. However, the reaction did not proceed in common organic sol-
ent 1,2-phenylenediamines and
Both the chloro and bromo ketoesters gave comparable results
for the formation of quinoxaline. Similarly, the electronic effect
a-halo-b-ketoesters (Table 1).
Table 1
Synthesis of quinoxaline-2-carboxylate derivatives using ionic liquid [bmim]BF4
Entry
1
a
-Halo, b-keto ester
1,2-Diamine
Producta
Time (min)
60
Yieldb (%)
90
Cl
H2N
O
N
N
OEt
EtO
H2N
a
O
O
1
1a
H2N
O
N
N
EtO
H2N
b
2
3
4
56
50
80
92
93
87
1b
1c
1d
1e
H2N
O
N
N
EtO
H2N
c
H2N
O
N
N
EtO
H2N
NO2
d
e
NO2
H2N
H2N
O
N
N
EtO
CO2Me
5
6
90
50
84
89
CO2Me
Br
2
H2N
H2N
O
OBn
N
BnO
O
a
O
N
2a

H. M. Meshram et al. / Tetrahedron Letters 51 (2010) 4313–4316
4315
Table 1 (continued)
Entry
a
-Halo, b-keto ester
1,2-Diamine
Producta
Time (min)
59
Yieldb (%)
H2N
O
N
N
BnO
7
8
H2N
b
91
93
89
94
2b
Br
H2N
O
EtO
N
OEt
F3C
H2N
a
45
50
40
O
O
F3C
N
3a
3
H2N
O
EtO
N
N
9
H2N
b
F3C
3b
3c
H2N
O
EtO
N
N
H2N
c
10
F3C
H2N
O
EtO
N
N
NO2
H2N
11
70
86
d
F3C
NO2
3d
3e
H2N
H2N
O
EtO
N
N
CO2Me
e
12
13
14
80
45
40
82
92
94
F3C
CO2Me
Br
H2N
H2N
O
MeO
Ph
N
Ph
OMe
O
O
a
b
N
4a
4
H2N
H2N
O
MeO
Ph
N
N
4b
Br
H2N
H2N
O
EtO
Ph
N
Ph
OEt
OEt
15
16
17
18
70
50
80
85
90
92
O
a
b
O
N
5
5a
H2N
H2N
O
EtO
Ph
N
N
5b
6a
Br
H2N
H2N
O
N
N
EtO
87
O
O
a
6
H2N
H2N
O
N
N
89c
EtO
b
6b
6c
H2N
H2N
O
N
N
EtO
19
20
75
90
c
H2N
H2N
O
N
N
EtO
NO2
95
99
87
85
d
e
NO2
6d
6e
H2N
H2N
O
N
N
EtO
CO2Me
21
CO2Me
a
Reaction conditions:
Isolated yields.
Isomeric products.
a-halo, b-keto ester (1.1 equiv), 1,2-phenylene diamine (1 equiv), ionic liquid [bmim]BF4 (2 mL) at rt.
b
c
of substituents on 1,2-diamine was studied in detail. The electron-
donating substituents enhance the rate of reaction and gave the
corresponding products in good yields (entries 3, 7, 10, 14, 16
and 19). It was interesting to note that the presence of methyl
group at fourth position of 1,2-phenylenediamine (entries 2, 9
and 18) gave two isomeric products (80:20) depending on the
course of cyclization. This phenomenon was not observed in the
case of electron-withdrawing substituents. This fact may be attrib-

4316
H. M. Meshram et al. / Tetrahedron Letters 51 (2010) 4313–4316
Kumar, D. A.; Prasad, B. R. V.; Goud, P. R. Helv. Chemi. Acta. 2010, 93, 648; (d)
Meshram, H. M.; Prasad, B. R. V.; Kumar, D. A. Tetrahedron Lett. In press.
17. (a) Varma, R. S.; Saini, R. K.; Meshram, H. M. Tetrahedron Lett. 1997, 38, 6525;
(b) Meshram, H. M.; Srinivas, D.; Yadav, J. S. Tetrahedron Lett. 1997, 38, 8743;
(c) Meshram, H. M.; Reddy, G. S.; Yadav, J. S. Tetrahedron Lett. 1997, 38, 891; (d)
Meshram, H. M.; Reddy, G. S.; Reddy, M. M.; Yadav, J. S. Tetrahedron Lett. 1998,
39, 4103; (e) Meshram, H. M.; Reddy, B. C.; Goud, P. R. Synth. Commun. 2009, 39,
2297; (f) Meshram, H. M.; Kumar, G. S.; Ramesh, P.; Reddy, B. C. Tetrahedron
Lett. 2010, 51, 2559.
uted to the electron-donating nature of methyl group which may
favour to increase the nucleophilic character of amine group. It
was noticed that electron-withdrawing substituents suppress the
reaction (entries 4, 5, 11, 12, 20 and 21) but favour the formation
of only one desired product. In addition, the functionalities like es-
ter remain unaffected. We believe that the procedure is simple,
convenient and does not require any aqueous work-up, thereby
avoiding the generation of waste, and may contribute to the area
of green chemistry.
18. (a) Boon, J. A.; Levinsky, J. A.; Pflug, J. L.; Wilkes, J. S. J. Org. Chem. 1986, 51, 480;
(b) Sheldon, R. Chem. Commun. 2001, 2399; (c) Harjani, J. R.; Nara, S. J.;
Salunkhe, M. M. Tetrahedron Lett. 2002, 43, 1127.
In summary, the ionic liquid was shown to be an effective and
useful alternative reaction medium for the preparation of 2-car-
boxylate quinoxaline derivatives. The present procedure offers sev-
eral unique advantages such as enhanced yields, shorter reaction
times, operational simplicity, mild reaction conditions, ease of iso-
lation of products and a greener aspect by avoiding the need for a
catalyst.
19. General procedure: A mixture of 1,2-phenylenediamine (1 mmol) and a-halo-b-
ketoesters (1.1 mmol) in [bmim]BF4 (2 mL) was stirred at rt for the appropriate
time (see Table 1). After completion of the reaction, as indicated by TLC, the
reaction mixture was extracted with diethyl ether (3 Â 10 mL). The combined
organic extracts were concentrated under vacuum and the resulting product
was directly charged on a silica gel (Merck, 60–120 mesh) column and eluted
with a mixture of ethyl acetate/n-hexane (1:9) to afford the corresponding
pure product. The residual ionic liquid was dried under vacuum and reused. All
the products were prepared by following the same procedure and
characterized by IR, mass and NMR.20
20. Spectral data for new compounds:
Acknowledgements
Compound 1b: Semi solid. 1H NMR (300 MHz, CDCl3): d 1.50 (3H, t, J = 6.83 Hz),
2.62 (3H, s), 2.90 (3H, s), 4.51 (2H, q, J = 6.83 Hz), 7.54 (1H, d, J = 8.78 Hz), 7.78
(1H, s), 8.02 (1H, d, J = 8.78 Hz). 13C NMR (75 MHz, CDCl3): d 14.1, 21.2, 23.1,
70.0, 127.7, 129.0, 136.6, 142.1, 148.4, 154.0, 161.0. MS (ESI) m/z 243 (M+Na),
P.R., G.S.K. and B.C.K.R. thank CSIR-UGC for the award of a fel-
lowship and Dr. J. S. Yadav, Director IICT, for his support and
encouragement.
231 (M+1); IR (KBr)
m = 2924, 1724, 1669, 1629, 1451, 1409, 1259, 1083,
804 cmÀ1. Compound 1d: Solid. Mp 73–74 °C; 1H NMR (300 MHz, CDCl3): d
1.52 (3H, t, J = 7.17 Hz), 2.98 (3H, s), 4.55 (2H, q, J = 7.17 Hz), 8.16 (1H, d,
J = 9.25 Hz), 8.60 (1H, dd, J = 2.45 Hz, J = 6.61 Hz), 9.07 (1H, d, J = 2.45 Hz). 13C
NMR (75 MHz, CDCl3): d 14.0, 23.1, 60.8, 122.4, 122.7, 129.3, 141.5, 143.2,
152.6, 158.6, 161. MS (ESI) m/z 284 (M+Na), 262 (M+1). IR (KBr): 3098, 2921,
2849, 1746, 1576, 1535, 1350, 1300, 1153, 1114, 1030, 906. Compound 1e:
Solid. Mp 57–58 °C. 1H NMR (300 MHz, CDCl3): d 1.51 (3H, t, J = 7.28 Hz), 2.98
(3H, s), 4.05 (3H, s), 4.55 (2H, q, J = 7.28 Hz), 8.07 (1H, d, J = 9.37 Hz), 8.40 (1H,
d, J = 9.37 Hz), 8.87 (1H, s). 13C NMR (75 MHz, CDCl3): d 14.0, 23.1, 51.6, 70.0,
127.5, 130.2, 133.2, 141.1, 143.1, 150.9, 156.4, 161.0, 166.0. MS (ESI) m/z 297
References and notes
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Crossley, M. J.; Johnston, L. A. Chem. Commun. 2002, 1122.
3. Brown, J. D.. In Taylor, C. E., Wipf, P., Eds.; The Chemistry of Heterocyclic
Compounds, Quinoxalines: Supplements II; John Wiley and Sons: New Jersey,
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R.; Pawar, R. P. Tetrahedron Lett. 2005, 46, 7183; (b) More, S. V.; Sastry, M. N. V.;
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(M+Na), 275 (M+1); IR (KBr)
m = 2925, 2854, 1719, 1617, 1553, 1445, 1318,
1236, 1086, 1020, 857, 758. Compound 3b: Semi solid. 1H NMR (300 MHz,
CDCl3): d 1.48 (3H, t, J = 6.83 Hz), 2.68 (3H, s), 4.53 (2H, q, J = 6.83 Hz), 7.78 (1H,
t, J = 7.80 Hz), 8.01 (1H, d, J = 8.78 Hz), 8.13 (1H, d, J = 8.78 Hz). 13C NMR
(75 MHz, CDCl3): d 14.1, 21.2, 61.0, 119.4, 129.3, 129.5, 138.2, 141.1, 142.0,
142.3, 161.0. MS (ESI) m/z 307 (M+Na), 285 (M+1); IR (KBr)
m = 2924, 2855,
1745, 1625, 1419, 1443, 1277, 1192, 1151, 1034, 827, 599 cmÀ1. Compound 3c:
Solid. Mp 66–68 °C. 1H NMR (300 MHz, CDCl3): d 1.49 (3H, t, J = 7.17 Hz), 2.57
(6H, s), 4.52 (2H, q, J = 7.17 Hz), 7.98 (2H, s). 13C NMR (75 MHz, CDCl3): d 14.0,
18.8, 60.9, 119.8, 129.2, 129.7, 140.3, 140.9, 151.1, 151.8, 161.0. MS (ESI) m/z
299 (M+1); IR (KBr)
m = 3075, 2926, 2855, 1737, 1628, 1594, 1418, 1336, 1203,
1083, 806, 616. Compound 3d: Semi solid. 1H NMR (300 MHz, CDCl3): d 1.50
(3H, t, J = 7.28 Hz), 4.57 (2H, q, J = 7.28 Hz), 8.44 (1H, d, J = 8.32 Hz), 8.72 (1H, d,
J = 8.32 Hz), 9.13 (1H, s). 13C NMR (75 MHz, CDCl3): d 14.0, 70.0, 119.7, 124.4,
125.8, 141.9, 144.9, 145.1, 146.5, 146.7, 160.0. MS (ESI) m/z 338 (M+Na). IR
(KBr): 2972, 2934, 1734, 1619, 1532, 1467, 1352 cmÀ1. Compound 3e: Semi
solid. 1H NMR (300 MHz, CDCl3): d 1.49 (2H, t, J = 6.83 Hz), 4.04 (3H, s), 4.55
(2H, q, J = 6.83 Hz), 8.29 (1H, t, J = 7.80 Hz), 8.52 (1H, t, J = 7.80 Hz), 8.92 (1H, d,
J = 8.78 Hz). 13C NMR (75 MHz, CDCl3): d 14.1, 51.5, 60.8, 119.8, 131.0, 133.6,
135.1, 142.0, 144.4, 145.2, 161.0, 165.9;. MS (ESI) m/z 351 (M+Na), 329 (M+1).
IR (KBr)
m = 2926, 2853, 1737, 1628, 1594, 1550, 1418, 1201, 1054, 806,
616 cmÀ1. Compound 6b: Semi solid. 1H NMR (300 MHz, CDCl3): d 1.40 (6H, d,
J = 6.79 Hz), 1.49 (3H, t, J = 7.17 Hz), 2.61 (3H, s), 3.65 (1H, m), 4.50 (2H, q,
J = 7.17 Hz), 7.40 (1H, dd, J = 1.70, J = 6.79 Hz), 7.85 (1H, d, J = 8.49 Hz), 8.0 (1H,
d, J = 8.49 Hz). 13C NMR (75 MHz, CDCl3): d 14.1, 21.3, 22.2, 32.4, 60.9, 127.87,
128.7, 136.6, 142.0, 148.4, 152.4, 161.2; MS (ESI) m/z 281 (M+Na), 259 (M+1).
IR (KBr)
m = 2972, 2929, 1731, 1621, 1552, 1322, 1229, 1182, 1101, 1057, 828.
Compound 6c: Solid. mp 67–69 °C. 1H NMR (300 MHz, CDCl3): d 1.30 (6H, d,
J = 6.24 Hz), 1.45 (3H, t, J = 7.28 Hz), 2.42 (3H, s), 2.44 (3H, s), 3.6 (1H, m), 4.44
(2H, q, J = 7.28 Hz), 7.77 (1H, s), 7.74 (1H, s). 13C NMR (75 MHz, CDCl3): d 14.0,
18.8, 22.1, 32.3, 60.9, 127.5, 129.1, 137.1, 141.9, 147.6, 150.0, 161.0. MS (ESI)
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Loh, T.-P. Synlett 2005, 959.
13. Yadav, J. S.; Reddy, B. V. S.; Premalatha, K. Adv. Synth. Catal. 2003, 345, 948.
14. Khurana, J. M.; Magoo, D. Tetrahedron Lett. 2009, 50, 7300.
15. Cui, D. M.; Ke, Y. K.; Zhuang, D. W.; Wang, Q.; Zhang, C. Tetrahedron Lett. 2010,
52, 980.
m/z 295 (M+Na), 273 (M+1). IR (KBr):
m = 2970, 2931, 1732, 1552, 1459, 1320,
1230, 1182, 1103, 1055, 827. Compound 6d: Semi solid. 1H NMR (300 MHz,
CDCl3): d 1.42 (6H, d, J = 6.79 Hz), 1.51 (3H, t, J = 6.79 Hz), 3.68 (1H, m), 4.54
(2H, q, J = 6.79 Hz), 8.20 (1H, d, J = 9.06 Hz), 8.55 (1H, dd, J = 9.06 Hz,
J = 11.33 Hz), 9.1 (1H, s). 13C NMR (75 MHz, CDCl3): d 14.1, 22.2, 32.2, 60.9,
122.4, 422.9, 141.5, 142.9, 152.6, 155.8, 161.0. MS (ESI) m/z 312 (M+Na), 290
(M+1). IR (KBr)
m = 2976, 2932, 2874, 1736, 1532, 1467, 1350, 1243, 1109,
1058, 849. Compound 6e: Semi solid. 1H NMR (300 MHz, CDCl3): d 1.42 (2H, d,
J = 7.28 Hz), 1.50 (3H, t, J = 7.28 Hz), 3.67 (1H, m), 4.0 (3H, s), 4.57 (2H, q,
J = 7.28 Hz), 8.10 (1H, d, J = 8.32 Hz), 8.37 (1H, d, J = 8.32 Hz), 8.82 (1H, s). 13C
NMR (75 MHz, CDCl3): d 14.0, 22.1, 32.3, 51.8, 60.9, 127.5, 130.4, 131.9, 133.4,
141.1, 143.1, 151.8, 154.5, 161.0, 165.9. MS (ESI) m/z 325 (M+Na). IR (KBr)
16. (a) Meshram, H. M.; Reddy, P. N.; Vishnu, P.; Sadhashiv, K.; Yadav, J. S.
Tetrahedron Lett. 2005, 46, 6607; (b) Meshram, H. M.; Reddy, P. N.; Vishnu, P.;
Sadhashiv, K.; Yadav, J. S. Tetrahedron Lett. 2006, 47, 991; (c) Meshram, H. M.;
m
= 2935, 2855, 1759, 1616, 1557, 1444, 1319, 1226, 1078, 1021, 850, 755.