Zirconium(IV) chloride as versatile catalyst for the expeditious synthesis of quinoxalines and pyrido[2,3-b]pyrazines under ambient conditions

Article abstract of DOI:10.1007/s11243-009-9294-9

Among the various transition metal chlorides, zirconium(IV) chloride was found to be an efficient catalyst for the rapid synthesis of a wide range of 2,3-dialkyl- and 2,3-diaryl-quinoxaline and pyrido[2,3-b]pyrazine derivatives in excellent yields at room temperature. The remarkable features of this catalytic process are the mild reaction conditions, quantitative yields, short reaction times, high conversions, tolerability of various functional groups, clean reaction profiles, and operational simplicity. Graphical Abstract: Among the various transition metal chlorides, zirconium(IV) chloride was found to be an efficient catalyst for the rapid synthesis of a wide range of 2,3-dialkyl- and 2,3-diaryl-quinoxaline and pyrido[2,3-b]pyrazine derivatives in excellent yields at room temperature. The remarkable features of this catalytic process are the mild reaction conditions, quantitative yields, short reaction times, high conversions, tolerability of various functional groups, clean reaction profiles, and operational simplicity.

Full text of DOI:10.1007/s11243-009-9294-9

Transition Met Chem (2010) 35:49–53
DOI 10.1007/s11243-009-9294-9
Zirconium(IV) chloride as versatile catalyst for the expeditious
synthesis of quinoxalines and pyrido[2,3-b]pyrazines
under ambient conditions
Kioumars Aghapoor
Farshid Mohsenzadeh
Hesam Daneshyar
•
Hossein Reza Darabi
Yadollah Balavar
•
•
•
Received: 1 September 2009 / Accepted: 5 October 2009 / Published online: 24 October 2009
Ó Springer Science+Business Media B.V. 2009
Abstract Among the various transition metal chlorides,
zirconium(IV) chloride was found to be an efficient catalyst
for the rapid synthesis of a wide range of 2,3-dialkyl- and 2,3-
diaryl-quinoxaline and pyrido[2,3-b]pyrazine derivatives in
excellent yields at room temperature. The remarkable fea-
tures of this catalytic process are the mild reaction condi-
tions, quantitative yields, short reaction times, high
conversions, tolerability of various functional groups, clean
reaction profiles, and operational simplicity.
iodine [26, 27], o-iodoxybenzoic acid [28], montmoril-
lonite K-10 [29], polyaniline sulfate [30], and metal
precursors such as cerium(IV) ammonium nitrate [31],
Zn[(L)proline] [32], Ni-nanoparticles [33], and zirconium
tetrakis(dodecyl sulfate) [34]. Although the various meth-
ods have some synthetic advantages individually, they still
suffer from one or more drawbacks, such as long reaction
time [29], the use of toxic [30] or corrosive solvent [28,
32], special apparatus [14–23, 25], high reaction tempera-
ture [24], not readily available materials [30, 32–34], and
the use of strong oxidants [31], strong acids [28], and toxic
catalysts [26, 27]. Besides, some procedures have restricted
activity and are not applicable to the entire family of
quinoxaline derivatives, the yields of some products are not
satisfactory, and the reactions often require cumbersome
product isolation. Thus, a practical and more efficient
alternative using an inexpensive, readily available and
green catalyst is still of interest for direct synthesis of
quinoxalines and pyrido[2,3-b]pyrazines under mild
conditions.
Introduction
One-stage (or direct) double condensation of 1,2-dicar-
bonyls with arene-1,2-diamines affording quinoxalines and
pyrido[2,3-b]pyrazines is an interesting target in modern
organic chemistry [1, 2]. These compounds play a key role
and have great synthetic potential for applications in aca-
demia and in many aspects of pharmaceutical and medic-
inal chemistry [3–12].
The traditional processes for the synthesis of quinoxa-
line rings generally require high reaction temperature,
strong acidic media, and mostly long reaction time in the
presence of ethanol or acetic acid with 34–85% yields [13].
During the last decade, several improved methods for
the synthesis of quinoxalines have been developed using
microwave [14–23], classical [24], or ball mill heating
Zirconium(IV) chloride is an eco-friendly, readily
available and low-cost Lewis acid catalyst possessing low
-
toxicity [LD50 (ZrCl , oral rat) = 1,688 mg kg ] and high
1
4
stability toward water and oxygen. The strong coordinating
4
?
2
2
-10
ability of Zr (Z /r is 22.22 e m ), ease and safety of
handling, and high catalytic activity makes it a potential
green catalyst. Its ability to work both in a solvent and under
solvent-free conditions is also other salient feature of this
catalyst [35, 36]. Zirconium(IV) chloride has already been
used for various organic transformations such as the direct
allylation of alkyl, aryl, and glycosyl 4-methoxyphenylcar-
binols [37], Mannich-type reaction for the synthesis of
b-branched Morita–Baylis–Hillman amino adducts [38], the
aldol condensation [39], Michael addition of heterocyclic
enamines [40], aza-Michael reaction of a,b-unsaturated
[
25]. Condensation of the starting materials has also been
carried out in the presence of a catalyst, such as molecular
HK .. AD ga hn ae ps oh oy ra rꢀ H. R. Darabi (&) ꢀ F. Mohsenzadeh ꢀ Y. Balavar ꢀ
Chemistry and Chemical Engineering Research Center of Iran,
Pajoohesh Blvd., km 17, Karaj Hwy, Tehran 14968-13151, Iran
e-mail: darabi@ccerci.ac.ir; r_darabi@yahoo.com
123

5
0
Transition Met Chem (2010) 35:49–53
enones [41], trimethylsilylation of alcohols and phenols
42], the synthesis of thioxo-3,4-dihydropyrimidin-2(1H)-
ones [43], trans-halohydrins [44], 4-chlorodihydropyran
45], thioethers and dithioethers [46], benzimidazoles [47],
Table 1 Transition metal chlorides’ catalytic effect on the synthesis
of 1d
[
Entry
Catalyst
–
Time (h)
GC yield (%)
[
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
1
1
1
11
83
75
31
78
69
18
59
21
28
8
and 1,5-benzodiazepines [48].
ZrCl
4
So far, our investigations on the quinoxaline condensa-
tion at room temperature consisted in using H NSO H–
FeCl
FeCl
3
2
ꢀ6H
ꢀ4H
2
O
O
2
3
2
CH OH [49] and NH Cl–CH OH [50] as effective catalytic
3
4
3
CuCl
CuCl
2
ꢀ2H
2
O
systems, giving quantitative yields of products. As part of
our program directed toward the development of efficient,
practical and eco-friendly procedures for the synthesis of
condensed benzo[N,N]-heterocyclic compounds [49–52],
2
PdCl
2
PtCl
2
CoCl
2
ꢀ6H
2
O
we herein wish to introduce ZrCl as a versatile and highly
4
1
0
NiCl
ZnCl
HgCl
2
effective catalyst for the synthesis of quinoxalines and
pyrido[2,3-b]pyrazines under very mild reaction conditions.
11
2
1
1
2
3
2
49
36
MnCl
2
ꢀ2H
2
O
Results and discussion
poor yield of 1d (Table 2, entries 7, 12, and 14). Clearly,
MeOH, EtOH, and THF stand out as the solvent of choice,
with a faster conversion (Table 2, entries 1, 2, 13). MeOH
was chosen as a solvent for further reaction optimization
because of its faster conversion, higher product yield,
cleaner workup procedure, and good availability.
In order to evaluate the efficiency of the catalyst, we
deliberately chose a strongly electron-withdrawing group
such as nitro on the aromatic ring of 1,2-diamine for the
model reaction. The reason of this judicious choice was
that the strong electron-withdrawing property of the nitro
group in 4-nitrobenzene-1,2-diamine decreases noticeably
the nucleophilicity of the amine group; hence, longer
reaction time is required. We set out to explore the possi-
bility of using a catalytic amount of common Lewis acids
of transition metals for the reaction of 4-nitrobenzene-1,2-
diamine (1.2 mmol) and benzil (1 mmol) in MeOH at a
fixed time (1 h) under ambient conditions (Scheme 1).
Our investigations revealed that the catalytic activity of
various transition metal chlorides was found to be of the
orderZrCl [CuCl ꢀ2H O[FeCl ꢀ6H O [CuCl [PtCl
In the study of catalyst loading, the effect of the relative
amounts of ZrCl on the outcome of the model reaction
4
was also studied. The increased loading of the catalyst
from 1 to 20 mol% at a fixed time (1 h) showed 5 mol% of
ZrCl4 in MeOH is the optimum catalyst ratio for this
conversion. To our satisfaction, a quantitative yield of
product 1d was obtained at room temperature within 4 h
(Table 3, entry 4).
These excellent preliminary results led us to expand the
generality of this catalyst to various arene-1,2-diamines and
1,2-dicarbonyls (Scheme 2). Most of the reactions took
5 min to complete at room temperature, although the yields
were highly dependent on the substrate used (Table 3). All of
4
2
2
3
2
2
2
[
HgCl , while the product 1d was obtained in low yields
2
when FeCl ꢀ4H O, PdCl , CoCl ꢀ6H O, NiCl , ZnCl , and
2
2
2
2
2
2
2
MnCl ꢀ2H O were used (Table 1). Hence, ZrCl exhib-
2
2
4
1
13
ited the highest catalytic activity with regard to the
transformation.
the products were characterized by H NMR, C NMR, and
MS spectral analysis. The results show that the nature of the
functional group on the aromatic ring of the substrate exerted
a strong influence on the time and the reaction yield. To
establish the scope and limitations of catalyst for quinoxaline
formation, the condensation between 4-nitrobenzene-
In the next step, the synthesis of 1d was performed in
various solvents in the presence of 5 mol% ZrCl at room
4
temperature. It was found that reaction in water, hexane,
dichloromethane, and 1,2-dichloroethane does not progress
0
(
Table 2, entries 8–11). The reaction in longer chain
1,2-diamine and 4,4 -dimethoxy-benzil was considered.
0
alcohols resulted in 42–50% yield of product (Table 2,
entries 3–6). The polar aprotic solvents, except THF, gave
The presence of the methoxy group in 4,4 -dimethoxy-
benzil reduces the electrophilicity of the carbonyl carbon
Scheme 1
O
N
N
NH2
Catalyst (5 mol%)
Solvent / RT
+
O
O N
2
O N
2
NH2
1
d
1
23

Transition Met Chem (2010) 35:49–53
51
Table 2 Solvent effect on the synthesis of 1d in the presence ZrCl
(
4
Accordingly, the combination of these substrates provided
the corresponding product 1i in 72% yield within 4 h. This
reaction can be completed within 4 h at 50 °C (Table 3,
entry 9).
5 mol %)
Entry
Solvent
Time (h)
GC yield (%)
1
2
3
4
5
6
7
8
9
CH
CH
CH
CH
CH
CH
CH
3
3
3
3
3
3
3
OH
1
1
1
1
1
1
1
1
1
1
1
1
1
1
83
73
49
42
50
45
35
1
CH
CH
2
OH
2
CH
2
OH
Experimental
CHOHCH
3
(CH
(CH
CN
2
)
)
2
CH
CH
2
OH
OH
Materials and methods
2
3
2
1
13
H and C NMR spectra were recorded on a Bruker-500
2
H O
spectrometer. All NMR samples were run in CDCl , and
3
C
6
H
14
–
chemical shifts are expressed as ppm relative to internal
10
11
12
13
14
CH
2
Cl
2
1
Me Si. Mass spectra were obtained on a Fisons instrument.
4
ClCH
DMF
THF
2
CH
2
Cl
–
Substrates were commercially available and used without
further purification.
23
74
19
DMSO
General procedure for the preparation of quinoxalines
and pyrido[2,3-b]pyrazines (1k–o)
0
through resonance and the strong electron-withdraw-
ing property of the nitro group in 4-nitrobenzene-1,2-dia-
mine decreases the nucleophilicity of the amine group.
To a stirred solution of benzil or 4,4 -dimethoxy-benzil
(1 mmol) in 5 mL methanol was added arene-1,2-diamine
(1.2 mmol) and crystalline zirconium(IV) chloride (5 mol%).
Table 3 Synthesis of quinoxalines and pyrido[2,3-b]pyrazines at room temperature catalyzed by ZrCl
4
0
a
Entry
R
R
Z
Product
Time
Yield (%)
M.p. (°C)
[Ref]
1
2
3
4
5
6
7
8
9
H
Ph
CH
CH
CH
CH
N
1a
1b
1c
1d
1e
1f
5 min
5 min
5 min
1 h/4 h
1 h
100
100
96
125–126
110–111
122–124
185–186
142–143
152–153
124–126
151–152
191.5–193
139–140
103–104
92–94
[51]
[51]
[53]
[51]
[51]
[25]
[25]
[31]
[28]
[54]
[50]
[50]
[50]
[50]
[55]
Me
Cl
NO
H
Ph
Ph
2
2
2
Ph
83/98
96
Ph
H
4-(MeO)-Ph
4-(MeO)-Ph
4-(MeO)-Ph
4-(MeO)-Ph
4-(MeO)-Ph
Me
CH
CH
CH
CH
N
30 min
30 min
2 h
100
100
97
Me
Cl
NO
H
1g
1h
1i
b
4 h
72 (96)
10
11
12
13
14
15
a
1j
4 h
95
H
CH
CH
CH
CH
N
1k
1l
5 min
5 min
5 min
5 min
5 min
100
100
100
100
100
Me
Cl
NO
H
Me
Me
1m
1n
1o
1
89–91
Me
131–133
143–144
Me
13
Yields refer to those of pure isolated products characterized by H NMR, C NMR, and MS spectral analyses, which is consistent with
literature values
b
The reaction was carried out at 50 °C
Scheme 2
NH2
NH2
O
O
R'
R'
N
N
R'
R'
ZrCl (5 mol%)
4
+
CH OH / RT
3
R
Z
R
Z
Z = CH, N
1a - o
123

5
2
Transition Met Chem (2010) 35:49–53
The mixture was stirred at room temperature for an
appropriate time (Table 3). After completion of the reac-
tion (monitored by TLC or GC), the precipitated solid was
collected by filtration and dried to afford the pure product
130.42, 130.59, 131.33 (2C), 131.49 (2C), 139.71 (2C),
143.50, 147.49, 155.17, 155.79, 160.80, 160.96; MS (EI),
?
m/z (rel. intensity %) 387 (M , 100), 356 (40), 254 (30),
208 (80), 133 (40).
1
. The identification of the isolated products was generally
1
2,3-Bis(4-methoxyphenyl)-pyrido[2,3-b]pyrazine (1j):
1
13
performed by H NMR, C NMR, and MS spectral anal-
yses after further crystallization.
139–140 °C (137–139 °C) [54]; H NMR (500 MHz,
CDCl ): d = 3.78 (s, 6H), 6.83 (dd, 4H), 7.49 (d, 2H), 7.59
3
1
d, 3H), 8.39 (d, 1H), 9.05 (br s, 1H); C NMR (125 MHz,
3
(
General procedure for the preparation of quinoxalines
CDCl ): d = 55.69, 55.74, 114.04 (2C), 114.32 (2C),
3
and pyrido[2,3-b]pyrazines (1k–o)
125.15, 131.13, 131.58, 131.67 (2C), 132.23 (2C), 136.25,
1
38.17, 150.22, 153.92, 154.56, 156.15, 160.96, 161.13;
?
MS (EI), m/z (rel. intensity %) 343 (M , 40), 312 (30), 133
(100), 103 (60), 90 (45).
To a stirred solution of butane-2,3-dione (1.3 mmol) in
5
mL methanol was added arene-1,2-diamine (1 mmol)
and crystalline zirconium(IV) chloride (5 mol%). The
mixture was stirred at room temperature for an appropriate
time (Table 3). After completion of the reaction (moni-
tored by TLC or GC), the reaction was quenched with
water and the product was extracted by CH Cl . The
2,3-Dimethylpyrido[2,3-b]pyrazine (1o): M.p. = 143–
1
144 °C (143.5–144 °C) [55]; H NMR (500 MHz, CDCl ):
3
d = 2.79 (s, 3H), 2.83 (s, 3H), 7.64 (dd, 1H), 8.35 (dd, 1H),
1
3
9.06 (dd, 1H); C NMR (125 MHz, CDCl ): d = 23.45,
3
23.92, 124.71, 136.30, 137.71, 150.67, 153.02, 155.42,
2
2
?
157.73; MS (EI), m/z (rel. intensity %) 159 (M , 100), 118
(75), 91 (15), 78 (18).
organic phase was evaporated, and the pure product 1k–o
was obtained without any further purification.
Selected spectroscopic data
Conclusion
2
,3-Diphenylpyrido[2,3-b]pyrazine(1e): M.p. = 142–143 °C
1
(
138 °C) [51] H NMR (500 MHz, CDCl ): d = 7.35 (m,
The direct condensation of 4-nitrobenzene-1,2-diamine and
benzil as a model reaction in the presence of common
transition metal chlorides was investigated. Among these
Lewis acids, zirconium(IV) chloride exhibited the highest
catalytic activity with regard to the transformation.
Following these results, a series of 1,2-dicarbonyls and
arene-1,2-diamines containing electron-donating and elec-
tron-withdrawing substituents underwent smooth double
3
6
1
H), 7.54 (d, 2H), 7.63 (d, 2H), 7.70 (dd, 1H), 8.50 (dd,
1
3
H), 9.15 (dd, 1H);
C NMR (125 MHz, CDCl3):
d = 125.62, 128.57 (2C), 128.84 (2C), 129.71, 129.86,
1
30.24 (2C), 130.70 (2C), 136.60, 138.49, 138.53, 138.98,
1
50.31, 154.51, 155.13, 156.73; MS (EI), m/z (rel. intensity
?
) 283 (M , 100), 179 (95), 103 (80), 77 (65).
%
2
,3-Bis(4-methoxyphenyl)quinoxaline (1f): M.p. =
1
1
52–153 °C (146–147 °C) [25] (145.5–146 °C) [56]; H
condensation in the presence of 5 mol % of ZrCl to produce
4
NMR (500 MHz, CDCl ): d = 3.88 (s, 6H), 6.92 (d, 4H),
7
a wide range of quinoxaline and pyrido[2,3-b]pyrazine
derivatives in excellent yields at room temperature. This
protocol offers general reactivity and is illustrated by the
energy-efficient and rapid preparation of condensed ben-
zo[N,N]-heterocyclic compounds making the procedure a
powerful tool from an industrial vantage point.
3
1
3
.54 (d, 4H), 7.76 (dd, 2H), 8.17 (dd, 2H); C NMR
(
125 MHz, CDCl ): d = 55.74, 114.21, 129.45, 129.95,
3
1
31.70, 132.18, 141.51, 153.45, 160.61; MS (EI), m/z (rel.
?
intensity %) 342 (M , 100), 328 (45), 312 (45), 209 (40),
66 (50).
-Methyl-2,3-bis(4-methoxyphenyl)quinoxaline (1g):
1
6
1
M.p. = 124–126 °C (123–125 °C) [25];
H
NMR
(
500 MHz, CDCl ): d = 2.64 (s, 3H), 3.88 (s, 6H), 6.91
3
(
dd, 4H), 7.52 (dd, 4H), 7.61 (dd, 1H), 7.94 (s, 1H), 8.05 (d,
1
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3
1
1
1
1
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