A mild and convenient synthesis of quinoxalines via cyclization-oxidation process using DABCO as catalyst

Article abstract of DOI:10.1016/j.tetlet.2010.01.107

An efficient and general method has been described for the synthesis of quinoxalines by the reaction of 1,2-diamines with phenacyl bromides in the presence of DABCO. The method is suitable for the preparation of functionalized quinoxalines.

Full text of DOI:10.1016/j.tetlet.2010.01.107

Tetrahedron Letters 51 (2010) 2580–2585
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A mild and convenient synthesis of quinoxalines via cyclization–oxidation
process using DABCO as catalyst
*
H. M. Meshram , G. Santosh Kumar, P. Ramesh, 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:
An efficient and general method has been described for the synthesis of quinoxalines by the reaction of
1,2-diamines with phenacyl bromides in the presence of DABCO. The method is suitable for the prepara-
tion of functionalized quinoxalines.
Received 18 November 2009
Revised 27 January 2010
Accepted 29 January 2010
Available online 4 February 2010
Ó 2010 Elsevier Ltd. All rights reserved.
Table 1
Quinoxaline is a core constituent of many pharmaceuticals as
well as agrochemicals.1 Quinoxaline ring is also found in antibiot-
ics such as echinomycin, leromycin, and actinomycin.2 In addition
to this, quinoxaline ring is a part of several bioactive natural prod-
ucts. Some of the quinoxaline derivatives were found to exhibit
broad spectrum of biological activity,1c while the other derivatives
of quinoxaline have found wide application in dyes,3a efficient
electroluminescent material,3b organic semiconductors,3c dehydro-
annulenes3d, and chemically controllable switches.3e Therefore,
these compounds have distinguished themselves as heterocycles
with chemical and biological significance. As a result, synthesis
of these molecules attracted considerable attention. A traditional
method for the constitution of quinoxaline ring involves the con-
densation of aryl 1,2-diamines with 1,2-dicarbonyl compounds,4
1,4-addition of 1,2-diamines to diazenylbutens5, and oxidation-
Screened bases for the reaction of phenacyl bromides with diamines
Entry
1
Basea
Conversionb (%)
Yieldc (%)
60
65
N
N
2
3
4
100
50
95
47
52
N
N
N
N
N
N
55
trapping of a
-hydroxy ketones with 1,2-diamines.6 Other recently,
N
reported methods accomplished the synthesis of quinoxaline by
the reaction of 1,2-diamines with phenacyl bromides in solid-
phase,7 or using heterogeneous catalyst like HClO4–SiO2.8 In addi-
tion to this b-cyclodextrin (b-CD)9 has been employed for the syn-
thesis of quinoxaline in heating condition. Though the reported
a
In a typical experiment, the 1,2-diamine (1 equiv) was added to a mixture of the
base (20 mol %) and the phenacyl bromide (1 equiv) in THF and stirred at rt.
b
Conversion of quinoxaline evaluated by 1H NMR.
Isolated yields.
c
R
R1
R2
R
R1
R2
H2N
H2N
N
N
DABCO (20 mol%)
THF, RT
+
Br
O
R= H,CH3,Cl,Br,CN
R1= H,CH3,COOMe,NO2
R2= H,CH3
Scheme 1.
* Corresponding author.
E-mail address: hmmeshram@yahoo.com (H.M. Meshram).
0040-4039/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2010.01.107

H. M. Meshram et al. / Tetrahedron Letters 51 (2010) 2580–2585
2581
ethers.14 To the best of our knowledge, there is no report on the
synthesis of quinoxalines using organic bases. In continuation of
our work in the area of green chemistry15 and particularly in the
development of non-metallic reagents,16 herein we wish to report
a simple, efficient, and general method for the preparation of
substituted quinoxalines by the reaction of o-phenylenediamines
with phenacyl bromides in the presence of DABCO (Scheme 1).
We have initiated our study by the reaction of phenacyl bro-
mide with o-phenylenediamines in the presence of different organ-
ic bases such as quinuclidine, DABCO, urotropine, and Troger’s base
in THF (Table 1).
Table 2
Quinoxaline formation in different solvent conditions
Entry
Solvent
Yielda (%)
1
2
3
4
5
Benzene
Toluene
THF
CH3CN
CH2Cl2
65
67
95
75
56
a
All the reactions are carried at rt.
R
It was observed that the reaction proceeded efficiently using
DABCO and resulted in high yield of desired product in short reac-
tion time (30 min). However, with other bases the reaction was
comparatively slow and gave less yield of the product even after
stretching the reaction time (1 h). In addition to this we have
screened acyclic tertiary amines such as TEA and N1,N1,N2-tri-
ethyl-N2-methylethane-1,2-diamine and found that the reaction
was very sluggish with poor yield (10–20%) even with extended
reaction time (4–5 h). We have attempted different ratios of DAB-
CO (10, 15, 20, 25, 30, 40 mol %) and observed that 20 mol % was
suitable for the optimum conversion. The increase in the mole ratio
of DABCO also did not improve the yield.
Br
2
O
N
N
+
Br
N
N
R
O
1
3
H2N
R1
R2
-HBr
-H2O
H2N
4
Further to optimize the reaction conditions, the reaction was
studied in different solvents such as benzene, toluene, dichloro-
methane, and acetonitrile. The reaction proceeded in all the sol-
vents with different degrees of conversion (Table 2). However,
the THF was the solvent of choice in terms of reaction time and
yield.
R
R
N
R1
R2
N
N
R1
R2
(O)
N
H
5
6
The formation of product may be explained by the reaction of
phenacyl bromide (2) with DABCO (1) which forms the quaternary
salt 3.17 Later it reacts with diamine and subsequent cyclization
and dehydrogenation result in expected product (6) (Scheme 2).
The scope of this DABCO-catalyzed quinoxaline formation was
explored under optimal condition18 and the results are summa-
rized in Table 3. We have studied the electronic effects of the sub-
stituents on the rate of the reaction and the mode of formation of
quinoxalines. It was observed that electron-rich substituents on
the diamine influence the reaction. For example, the presence of
highly electron-rich substituents (entry 21) on the diamine ring
activates the amino group at para position, which further attack
on ion pair to form the single isomer through intermediate 7. This
phenomenon was not observed with weak electron-donating sub-
stituents like methyl. However, in the case of 4-methyl 1,2-phenyl-
enediamine (entries 2, 11, 14 and 18) gave the two isomeric
products depending on the course of cyclization. It was observed
Scheme 2. Plausible mechanism for the quinoxaline formation.
methods provide good yields, these methods suffer from tedious
work-up, longer reaction time, use of metal catalyst, and narrow
scope of substrates. Moreover, some of the methods have some
drawbacks such as unsatisfactory yields, expensive and detrimen-
tal metal reagents. In view of this, there is still need to develop a
general and efficient method for the synthesis of more functional-
ized quinoxaline derivatives.
Recently, use of non-metallic reagents is an area of growing
interest because of environmental regulations. Among the various
organic bases, 1,4-diazabicyclo[2,2,2]octane (DABCO) has been em-
ployed as a organic-hindered base to bring about various organic
transformations like deprotection of peptides,10 as a catalyst for
the Baylis–Hillman reaction,11 for isoxazoles preparation,12 o-alky-
lations of phenols13, and deprotection of benzylic trimethylsilyl
H2N
H2N
N
+
N
Br
N
D
H2N
R
D
N
O
H2N
D
N
+
R
7
Br
N
D = electron donating
substituents
R
N
N
O
+
Br
N
N
W
3
H2N
W
R
H2N
W
O
H2N
R
8
H2N
W = electron withdrawing
substituents
Scheme 3. Detailed mechanism for the quinoxaline formation.

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H. M. Meshram et al. / Tetrahedron Letters 51 (2010) 2580–2585
Table 3
Synthesis of quinoxalines in the presence of DABCOa
Entry
Phenacyl bromide
1,2-Diamine
Product
Time (min)
Yieldb (%)
H2N
N
N
Br
H2N
1
30
90
O
1
a
1a
H2N
H2N
N
N
2
3
26
25
92c
1b
b
H2N
N
N
H2N
93
c
1c
H2N
N
N
H2N
NO2
4
40
87
NO2
d
1d
H2N
N
N
H2N
CO2Me
5
6
7
37
50
32
89
84c
90
CO2Me
e
1e
H2N
N
N
N
H2N
H2N
H2N
N
1f
f
Cl
Cl
Cl
N
N
Br
O
a
2
2a
H2N
H2N
N
N
8
9
30
30
91
92
b
2b
3a
Br
H2N
H2N
Br
Br
N
N
Br
3
a
O
H2N
H2N
N
N
CO2Me
10
11
40
30
86
b
CO Me
2
3b
H2N
H2N
N
Br
90c
N
3c
c

H. M. Meshram et al. / Tetrahedron Letters 51 (2010) 2580–2585
2583
Table 3 (continued)
Entry
Phenacyl bromide
1,2-Diamine
Product
Time (min)
35
Yieldb (%)
H2N
N
N
Br
12
90
H2N
4
a
O
4a
H2N
H2N
N
13
14
15
30
33
40
92
90c
88
b
c
N
N
4b
H2N
N
H2N
H2N
4c
4d
N
N
H2N
NO2
d
e
a
NO2
H2N
H2N
N
N
16
37
89
CO2Me
CO2Me
4e
NC
H2N
H2N
NC
N
17
18
27
28
93
Br
5
O
N
N
5a
H2N
NC
NC
92c
N
H2N
H2N
5b
b
N
N
19
H2N
NO2
30
90
c
5cNO
2
H2N
H2N
NC
N
N
20
21
30
30
90
90
dCO Me
2
5dCO Me
2
H2N
H2N
OMe
N
N
Br
OMe
O
g
a
1
1g
O2N
O2N
H2N
H2N
N
N
Br
22
23
45
35
85
O
6
7
6a
HO
HO
N
Br
91
O
N
7a
(continued on next page)

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H. M. Meshram et al. / Tetrahedron Letters 51 (2010) 2580–2585
Table 3 (continued)
Entry
Phenacyl bromide
1,2-Diamine
Product
Time (min)
25
Yieldb (%)
MeO
MeO
N
N
Br
Br
24
92
O
8
8a
9a
Et2N
Et2N
N
25
32
90
O
N
9
a
Reaction conditions: phenacyl bromide (1 equiv), 1,2-diamines (1 equiv), DABCO (20 mol %), in THF (4 ml).
Isolated products.
Mixture of isomers (8:2).
b
c
Suling, W. J.; Reynolds, R. C. J. Med. Chem. 2002, 45, 5604; (d) Gazit, A.; App, H.;
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2. Brown In, J. D., 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. J.; Velusamy, M.; Lin, J. T.; Chuen, C.-H.; Tao, Y.-T. Chem. Mater. 2005, 17,
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Mater. Chem 2001, 11, 2238; (d) Sascha, O.; Ru diger, F. Synlett. 2004, 1509; (e)
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Yao, C.-F. Tetrahedron Lett. 2005, 46, 6345; (d) Guo, W. X.; Jin, H. L.; Chen, J. X.;
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that the corresponding 2-aryl-7-methyl quinoxaline was the major
product, whereas the other isomer 2-aryl-6-methyl quinoxaline
was obtained as a minor product. While the symmetric diamines
like 4,5-dimethyl-1-2-phenylenediamine (entries 3, 8, 9, 13 and
17) with phenacyl bromides resulted in the corresponding quinox-
aline as a sole product in high yields. Further it is observed that the
presence of electron-withdrawing substituents (entries 4, 5, 10, 15,
16, 19, and 20) on the diamine ring deactivates the para amino
group. Due to this, another amino group first participates in the
reaction and leads to intermediate 8 which on cyclization and oxi-
dation gives the corresponding product (Scheme 3).
Next we have extended this protocol for the heterocyclic dia-
mines. Thus 1,2-pyridine diamine (entry 6) reacted with phenacyl
bromide and led to isomers of products in good yields. From Table
3 it can be seen that different substituted phenacyl bromides re-
acted with substituted 1,2-phenylenediamines and provided func-
tionalized quinoxalines. We have also examined phenacyl
bromides having different substituents such as NO2, CN, Cl, Br,
OH, OMe, N,N-dialkyl, and Me. The electron-rich functionalities
(entries 7–9, 10–16, and 23–25) influence the reaction and furnish
the corresponding quinoxalines in high yield. Whereas the elec-
tron-withdrawing substituents (entries 17–20 and 22) on phenacyl
bromide gave comparatively low yield of quinoxaline under iden-
tical conditions. It is worthy to mention that the present method
provides access for the synthesis of new functionalized quinoxa-
lines (entry 5, 10, 16–19, and 20) which have not been synthesized
earlier. These quinoxalines bearing the nitrile and ester functional-
ities may provide scope for further extension to build up pharma-
ceutically important molecules.
14. Sharafi, T.; Heravi, M. M. Phosphorus, Sulfur Silicon 2004, 179, 2437.
15. (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.;
Kumar, D. A.; Prasad, B. R. V.; Goud, P. R. Helv.Chemi. Acta., in press.
16. (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.
In conclusion, we have demonstrated an efficient and mild
method for the synthesis of functionalized quinoxalines using
DABCO as a catalyst. This method is applicable for a variety of
phenacyl bromides and o-phenylenediamines. Moreover, this pro-
tocol provides access for the synthesis of functionalized
quinoxalines.
17. Fan, M.; Guo, L.; Liu, X.; Liu, W.; Liang, Y. Synthesis 2005, 391.
18. General procedure:
A mixture of phenacyl bromide (1 equiv) and DABCO
(20 mol %) was stirred at rt for 5 min. Then 0-phenylenediamine (1 equiv) was
added slowly and the resultant mixture was stirred at rt for stipulated time
(see Table 3). After completion of the reaction, as indicated by TLC, the mixture
was poured into water. It was extracted with ethylacetate (3 Â 15 ml), dried
over Na2SO4, and evaporated under reduced pressure. The crude product was
purified by passing through small pad of silica gel to give pure product (ethyl
acetate:hexane). All the compounds were characterized by 1H NMR, 13C NMR,
mass, and IR spectral data.19
Acknowledgments
G.S.K., P.R., and B.C.K.R. thank CSIR-UGC for the award of a fel-
lowship and to Dr. J. S. Yadav, Director IICT, for his support and
encouragement.
19. Spectral data for new compounds:
Compound 1e: mp 152–154 °C; 1H NMR (300 MHz, CDCl3): d 4.0 (s, 3H), 7.58
(m, 3H), 8.16 (d, 1H, J = 8.309 Hz), 8.24 (d, 2H, J = 8.309 Hz), 8.35 (d, 1H,
J = 2.26 Hz), 8.78 (s, 1H), 9.38 (s, 1H). 13C NMR (75 MHz, CDCl3): 52.5, 127.6,
129.1, 129.6, 129.7, 130.7, 131.5, 135.9, 140.4, 144.2, 153.1, 166.1. IR (KBr)
References and notes
1. (a) Sakata, G.; Makino, K.; Kurasawa, Y. Heterocycles 1988, 27, 2481; (b) Sato, N.
In Comprehensive Heterocyclic Chemistry II; Katritzky, A. R., Rees, C. W., Scriven,
E. F., Eds.; Elsevier Science Ltd: Oxford, 1996; p 6. Chapter 6.03; (c) Seitz, L. E.;
m
= 2923, 2852, 1714, 1542, 1444, 1291, 1251, 1172, 1089, 770, 686 cmÀ1. MS
(ESI) m/z 265 (M+1). Compound 3b: mp 134–136 °C; 1H NMR (300 MHz, CDCl3):
d 4.05 (s, 3H), 7.7 (d, 2H, J = 1.88 Hz), 8.16 (dd, 3H, J = 2.83, J = 3.02 Hz), 8.38 (d,

H. M. Meshram et al. / Tetrahedron Letters 51 (2010) 2580–2585
2585
1H, J = 1.88 Hz), 8.79 (d, 1H, J = 1.88 Hz), 9.37 (s, 1H). 13C NMR (75 MHz, CDCl3):
52.3, 127.2, 127.6, 128.1, 130.7, 131.9, 132.8, 134.3, 135.2, 137.9, 141.5, 149.9,
165.8. IR (KBr) = 2925, 2854, 1726, 1584, 1458, 1291, 1170, 1088, 1005, 828,
756, 558 cmÀ1. MS (ESI) m/z 341 (M+2). Compound 3c: mp 118–120 °C; 1H NMR
(300 MHz, CDCl3): 2.62 (s, 3H), 7.58 (d, 1H, J = 8.49 Hz), 7.68 (d, 3H,
1021, 842, 546 cmÀ1. MS (ESI) m/z 259 (M+). Compound 5b: mp 159–161 °C; 1
H
NMR (300 MHz, CDCl3): d 2.62 (s, 3H), 7.6 (t, 1H, J = 8.309 Hz), 7.82 (d, 2H,
J = 8.309 Hz), 7.86 (d, 1H, J = 4.34 Hz), 8.0 (d, 1H, J = 2.63 Hz), 8.34 (d, 2H,
J = 8.309 Hz), 9.25 (s, 1H). 13C NMR (75 MHz, CDCl3): 21.6, 113.3, 117.4, 126.5,
m
d
132.0, 133.6, 139.5, 140.4, 140.8, 142.5, 148.2. IR (KBr) m = 2923, 2853, 2224,
J = 8.49 Hz), 7.88 (d, 1H, J = 7.74 Hz), 7.98 (d, 1H, J = 8.49 Hz), 8.10 (d, 2H,
1606, 1492, 1440, 1308, 1196, 1049, 959, 843, 718, 539 cmÀ1. MS (ESI) m/z 246
(M+1). Compound 5c: mp 209–211 °C; 1H NMR (300 MHz, CDCl3): d 7.9 (d, 2H,
J = 8.39 Hz), 8.32 (d, 1H, J = 8.39 Hz), 8.5 (d, 2H, J = 8.39 Hz), 8.6 (d, 1H,
J = 8.39 Hz), 9.0 (s, 1H), 9.66 (s, 1H). MS (ESI) m/z 276 (M+). 13C NMR (75 MHz,
CDCl3): 97.9, 112.6, 117.8, 124.1, 124.5, 126.4, 133.9, 135.2, 139.2, 142.2, 143.4,
J = 8.49 Hz), 9.2 (s, 1H). 13C NMR (75 MHz, CDCl3): 21.8, 124.8, 126.1, 127.6,
129.0, 132.2, 132.7, 135.5, 140.7, 141.2, 141.5, 142.1, 150.5. IR (KBr)
m = 2925,
2854, 1584, 1458, 1086, 959, 757, 709 cmÀ1. MS (ESI) m/z 299 (M+). Compound
4e: mp 149–151 °C; 1H NMR (300 MHz, CDCl3): d 2.47 (s, 3H), 4.03 (s, 3H), 7.35
(d, 2H, J = 7.554 Hz), 8.13 (d, 3H, J = 8.309 Hz), 8.35 (dd, 1H, J = 1,51 Hz), 8.77 (d,
1H, J = 1.51 Hz), 9.66 (s, 1H). 13C NMR (75 MHz, CDCl3): 21.4, 52.5, 127.5, 128.7,
150.2, 150.5. IR (KBr)
m .
= 2928, 2843, 2236, 1570, 1459, 1263, 1112, 830 cmÀ1
Compound 5d: mp 212–214 °C; 1H NMR (300 MHz, CDCl3): d 4.0 (s, 3H), 7.84 (d,
2H, J = 7.55 Hz), 8.2 (d, 1H, J = 9.06 Hz), 8.4 (d, 3H, J = 7.554 Hz), 8.83 (d, 1H,
J = 9.06 Hz), 9.42 (s, 1H). 13C NMR (75 MHz, CDCl3): 51.1, 112.4, 116.7, 124.2,
127.9, 129.2, 131.2, 132.6, 133.9, 134.8, 138.2, 141.4, 142.2, 148.4, 165.9. IR
129.1, 129.9, 131.6, 133.2, 140.4, 141.2, 144.7, 166.2. IR (KBr)
m = 2923, 2854,
1721, 1606, 1541, 1431, 1293, 1172, 1088, 760 cmÀ1. MS (ESI) m/z 279 (M+1).
Compound 5a: mp 157–160 °C; 1H NMR (300 MHz, CDCl3): d 2.55 (s, 6H), 7.8 (s,
1H), 7.85 (s, 1H), 8.05 (d, 2H, J = 8.309 Hz), 8.33 (d, 2H, J = 8.309 Hz), 9.2 (s, 1H).
13C NMR (75 MHz, CDCl3): 20.3, 113.1, 117.7, 127.6, 132.3, 132.6, 139.7, 140.6,
(KBr)
m
= 2924, 2853, 2221, 1725, 1535, 1458, 1247, 1089, 955, 759 cmÀ1. MS
(ESI) m/z 290 (M+1).
140.9, 141.5, 148.4. IR (KBr)
m = 2924, 2854, 2221, 1688, 1456, 1260, 1108,