Highly selective synthesis of mono- and bis-4,5-dihydropyrrolo[1,2-a]quinoxalines catalyzed by sustainable supported acidic ionic liquid in water media

Article abstract of DOI:10.1007/s00706-018-2142-x

Abstract: Preparation of substituted as well as the selective synthesis of mono- and bis-4,5-dihydropyrrolo[1,2-a]quinoxalines using a highly efficient, sustainable, and reusable supported acidic ionic liquid is reported. The reaction method is ecofriendl

Full text of DOI:10.1007/s00706-018-2142-x

Monatsh Chem
https://doi.org/10.1007/s00706-018-2142-x
ORIGINAL PAPER
Highly selective synthesis of mono- and bis-4,5-
dihydropyrrolo[1,2-a]quinoxalines catalyzed by sustainable
supported acidic ionic liquid in water media
Raziyeh Rashidi1 Mahboobeh Nasr-Esfahani1 Iraj Mohammadpoor-Baltork1
•
•
•
Shahram Tangestaninejad1 Majid Moghadam1 Valiollah Mirkhani1
•
•
Received: 10 October 2017 / Accepted: 1 January 2018
Ó Springer-Verlag GmbH Austria, part of Springer Nature 2018
Abstract Preparation of substituted as well as the selective
synthesis of mono- and bis-4,5-dihydropyrrolo[1,2-
a]quinoxalines using a highly efficient, sustainable, and
reusable supported acidic ionic liquid is reported. The
reaction method is ecofriendly and has the advantages of
mild conditions, green solvent (H2O), short reaction times,
and a reusable acidic catalyst.
Introduction
Quinoxaline is an essential category of nitrogen-containing
heterocycles, which represent a broad series of pharma-
cological properties [1]. They were also employed as
constructing blocks for the preparation of organic semi-
conductors, dyes, and macrocyclic receptors [2, 3]. Simi-
larly, pyrrole is usually the core fragment of various natural
and unnatural compounds with vital properties, both in
materials science and pharmacology [4, 5]. The integration
of quinoxaline and pyrrole into a single molecule exhibits
new or improved biological properties [6, 7]. Particularly,
4,5-dihydropyrrolo[1,2-a]quinoxaline derivatives (Fig. 1)
have been described as antifungal [8], cannabinoid type 1
receptor (CB1R) antagonists [6, 9], estrogen receptor
modifier [6, 10], and Nogo receptor modifier effects
[6, 11]. Due to a wide range of applications, the develop-
ment of simple methods for preparation of 4,5-dihydropy-
rrolo[1,2-a]quinoxalines is essential. A Pictet–Spengler-
type reaction in the presence of acidic catalyst [12] of 1-(2-
aminophenyl)pyrrole through an aldehyde is the most
common method for synthesis of these heterocycles.
Among the acid catalysts, Brønsted acid such as
hydrochloric acid [13], acetic acid [14], sulfamic acid [15],
p-dodecylbenzenesulfonic acid [16], p-toluenesulfonic acid
[17], and AlCl3 [18] were reported for the production of
4,5-dihydropyrrolo[1,2-a]quinoxalines.
Graphical abstract
Keywords Heterogeneous catalysis Á Heterocycles Á 4,5-
Dihydropyrrolo[1,2-a]quinoxalines Á Green chemistry Á
Selective synthesis
Electronic supplementary material The online version of this
article (https://doi.org/10.1007/s00706-018-2142-x) contains supple-
mentary material, which is available to authorized users.
Recently, acidic ionic liquid (AIL) became much sig-
nificant due to useful characteristics such as high catalytic
efficiency stability in water and air, and easy separation
[19–21]. Despite extensive applications of AILs, the
chemical companies prefer to use a heterogeneous catalyst
system because of the easy recovery and reusability of
them; thus, using supported acidic ionic liquids (SAILs) is
extremely desirable. In this system, the acidic ionic liquid
& Iraj Mohammadpoor-Baltork
imbaltork@sci.ui.ac.ir
& Shahram Tangestaninejad
stanges@sci.ui.ac.ir
1
Catalysis Division, Department of Chemistry, University of
Isfahan, Isfahan 81746-73441, Iran
123

R. Rashidi et al.
Fig. 1 Some biologically active 4,5-dihydropyrrolo[1,2-a]quinoxalines
is immobilized on the surface of a high porous and area
support material [22–26]. Motivated by the unique prop-
erties and many applications of nanostructures supported
ILs [27–30], herein, we describe a convenient method for
the selective synthesis of mono- and bis-4,5-dihydropy-
rrolo[1,2-a]quinoxalines in the presence of a highly effi-
cient, green, and recoverable SAIL catalyst.
the technical analysis such as FT-IR spectroscopy, ele-
mental analysis, UV–Vis (DSR), SEM, and EDX. The
sulfur content of [PPy]HSO4@nSiO2 catalyst was mea-
sured 0.52 by CHNS analysis. Based on this value, the
amount of IL which is supported on the nSiO2 is about
0.16 mmol per gram of catalyst.
The IR spectra of every preparation steps of catalyst
(Scheme 1) were shown in Fig. 2a. The FT-IR spectrum of
[PPy]HSO4@nSiO2 catalyst showed a characteristic band
at 1637 cm-1 (C=N) and several other bands at 3050,
2902, and 1436 cm-1, which are due to C–H stretching and
vibrational of the pyridine ring and alkyl chain [31]. In
addition, the characteristic band at 1267 cm-1 (S–O–H)
was observed [32], but the characteristic S=O band
(1100–1180 cm-1) [32] cannot be determined due to
overlapping by Si-O band.
Results and discussion
Preparation and characterization
of [PPy]HSO4@nSiO2
Scheme 1 illustrates the procedure of preparation of acidic
supported ionic liquid ([PPy]HSO4@nSiO2) by covalent
addition of the IL onto the silica nanoparticle surface. The
process of catalyst preparation was investigated with
The diffuse reflectance UV–Vis spectra of pure nSiO2
and [PPy]HSO4@nSiO2 are shown in Fig. 2b. The UV–Vis
spectrum of catalyst showed three significant absorption
bands at 216, 263, and 302 nm. The strong and sharp
absorption band at 263 and medium band at 216 nm
appeared, relating to p ? p* and n ? p* transition of
C=N, respectively, resulting from the attachment of pyr-
idine to nSiO2 [33]. The band at 302 nm was related to
hydrogen sulfate anion [34].
Scheme 1
The SEM images of the nSiO2 and [PPy]HSO4@nSiO2
catalyst (Fig. 3) demonstrated that the morphology of the
two samples is diverse. Moreover, the energy dispersive
X-ray (EDX) analysis of [PPy]HSO4@nSiO2 indicates the
presence of all the expected elements C, N, S, O, and Si
(Fig. 4). The results characterize that the IL has effectively
been immobilized on the nSiO2 surface.
Preparation of 4,5-dihydropyrrolo[1,2-a]quinoxaline
derivatives
In an initial study on the synthesis of 4,5-dihydropy-
rrolo[1,2-a]quinoxaline, we screened the reaction
123

Highly selective synthesis of mono- and bis-4,5-dihydropyrrolo[1,2-a]quinoxalines catalyzed…
Fig. 2 Characterization of catalyst: a FT-IR and b UV–Vis
Fig. 3 SEM images of a the nSiO2 and b [PPy]HSO4@nSiO2
desired product 3a. It was also found that decreasing
temperature lower than 70 °C reduced the yield of the
product. To show the effectiveness of [PPy]HSO4@nSiO2
catalyst, we have performed this reaction in the presence of
other catalysts and ILs like as ZnCl2, H3PW12O40,
[PPy]Cl@nSiO2, [PPy]Cl (propylpyridinium chloride), and
[PPy]HSO4 (propylpyridinium hydrogen sulfate). The
results are listed in Table 1, which clearly indicate that
[PPy]HSO4@nSiO2 is the suitable catalyst for the proposed
transformation.
Verma et al. reported using AlCl3 as a catalyst in the
same reaction produced a mixture of 4,5-dihydropy-
rrolo[1,2-a]quinoxaline and pyrrolo[1,2-a]quinoxaline
(oxidized form). Specially, the yield of pyrrolo[1,2-
a]quinoxaline increased by the passage of time [18].
Accordingly, we performed the modal reaction for 24 h in
the presence of our catalyst, but the oxidized product has
not been produced (Table 1, entry 15).
Fig. 4 EDX analysis of [PPy]HSO4@nSiO2
parameters such as solvent, the catalyst amount, and tem-
perature in the model reaction of 1-(2-aminophenyl)pyrrole
(1), 4-nitrobenzaldehyde (2a), and [PPy]HSO4@nSiO2
catalyst (Table 1, entries 1–14). The results exhibited that
50 mg of the [PPy]HSO4@nSiO2 (0.8 mol%) efficiently
catalyzed the reaction at 70 °C in water media to give the
123

R. Rashidi et al.
Table 1 Optimization of the reaction conditions
Entry
Catalyst/mol%
Solvent
Temp./°C
Yield/%a
1
[PPy]HSO4@nSiO2 (0.8)
[PPy]HSO4@nSiO2 (0.8)
[PPy]HSO4@nSiO2 (0.8)
[PPy]HSO4@nSiO2 (0.8)
[PPy]HSO4@nSiO2 (0.8)
[PPy]HSO4@nSiO2 (0.8)
[PPy]HSO4@nSiO2 (0.8)
[PPy]HSO4@nSiO2 (1.0)
[PPy]HSO4@nSiO2 (0.7)
[PPy]HSO4@nSiO2 (0.6)
[PPy]HSO4@nSiO2 (0.8)
[PPy]HSO4@nSiO2(0.8)
[PPy]HSO4@nSiO2 (0.8)
[PPy]HSO4@nSiO2 (0.8)
[PPy]HSO4@nSiO2 (0.8)
–
Benzene
THF
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
80
70
2
60
3
CH2Cl2
CHCl3
EtOH
EtOH:H2O
H2O
65
4
75
5
95
6
99
7
99
8
H2O
99
9
H2O
85
10
11
12
13
14
15b
16
17
18
19
20
21
22
23
H2O
60
H2O
99
H2O
70
99
H2O
50
45
H2O
25
Trace
99
H2O
70
H2O
70
Trace
70
ZnCl2 (0.8)
H2O
70
H3PW12O40 (0.8)
H2O
70
65
nSiO2 (50 mg)
H2O
70
Trace
20
[PPy]Cl@nSiO2 (50 mg)
[PPy]Cl (0.8)
H2O
70
H2O
70
15
[PPy]HSO4 (0.8)
H2O
70
60
HOAc (0.8)
H2O
70
48
Model reaction: 1-(2-aminophenyl)pyrrol (1, 1.0 mmol), 4-nitrobenzaldehyde (2a, 1.0 mmol), 5 cm3 solvent
aIsolated yield
bThe reaction was continued for 24 h on air
Production of 4,5-dihydropyrrolo[1,2-a]quinoxaline
using [PPy]HSO4@nSiO2 catalyst
been synthesized and reported for the first time. In addition,
the selectivity of this method was also investigated in a
binary mixture of 4-nitrobenzaldehyde and 1-heptanal. The
aromatic aldehyde was converted to the corresponding 4,5-
dihydropyrrolo[1,2-a]quinoxaline in 95% yield, whereas
trace amount of aliphatic aldehyde has been converted to
desired product (Scheme 2).
The efficiency of [PPy]HSO4@nSiO2 catalyst for produc-
tion of various 4,5-dihydropyrrolo[1,2-a]quinoxaline was
considered and the results are summarized in Table 2.
Various aromatic aldehydes, including alkoxy, halo, nitro,
or even cinnamic groups, were well reacted with 1-(2-
aminophenyl)pyrrole in the presence of our catalyst. It was
useful that the desired products achieved from the reaction
of heterocyclic and polycyclic aldehydes (3j–3m). Ali-
phatic aldehyde such as 1-heptanal was used and produced
the desired product (3n). Many of these compounds have
Selective synthesis of mono- and bis-4,5-
dihydropyrrolo[1,2-a]quinoxaline
For the first time, selective synthesis of mono- and bis-4,5-
dihydropyrrolo[1,2-a]quinoxaline from dialdehydes could
123

Highly selective synthesis of mono- and bis-4,5-dihydropyrrolo[1,2-a]quinoxalines catalyzed…
Table 2 Synthesis of substituted 4,5-dihydropyrrolo[1,2-a]quinoxalines 3
Entry
R
Product
Time/min
Yield/%a
1
4-NO2C6H4
3a
3b
3c
3d
3e
3f
10
10
10
20
20
15
15
15
30
45
15
35
40
25
99
98
98
96
97
98
97
99
90
95
98
85
98
85
2
3-NO2C6H4
3
2-NO2C6H4
4
4-ClC6H4
5
2,6-(Cl)2C6H3
4-MeOC6H4
6
7
3-MeOC6H4
3g
3h
3i
8
3,4-(MeO)2C6H3
Cinnamyl
9
10
11
12
13
14
Anthracen-9-yl
Thiophen-3-yl
1H-Indol-3-yl
6-Chloro-4-oxo-4H-chromen-3-yl
Hexyl
3j
3k
3l
3m
3n
Scheme 2
be achieved with this procedure. In this respect, using a 1:1
molar ratio of 1-(2-aminophenyl)pyrrole and dialdehydes
through [PPy]HSO4@nSiO2, only one formyl group reacted
selectively and the corresponding mono-4,5-dihydropy-
rrolo[1,2-a]quinoxalines 3o–3r were obtained in good yields
(Scheme 3). The remaining formyl group can be modified to
some other relevant functional groups and produced various
of 4,5-dihydropyrrolo[1,2-a]quinoxalines.
produced highly flexible bis-4,5-dihydropyrrolo[1,2-
a]quinoxalines, which can be used as ligands for com-
plexation with metals and various ions.
Production of 4-methyl-4,5-dihydropyrrolo[1,2-
a]quinoxalines
Encouraged by these successes, we next turned our atten-
tion to examine the activity of this catalytic system for the
production of 4-methyl-4,5-dihydropyrrolo[1,2-a]quinoxa-
lines from acetophenone derivatives. As shown in Table 3,
different acetophenones with alkyl, halo, nitro substituent
were smoothly reacted with 1-(2-aminophenyl)pyrrole and
afforded the desired products in moderate-to-high yields.
Whereas using a 2:1 molar ratio of 1-(2-aminophe-
nyl)pyrrole and dialdehydes in the same reaction condi-
tions proceeded efficiently and produced the corresponding
bis-4,5-dihydropyrrolo[1,2-a]quinoxalines in high yields
(Scheme 4). The use of dialdehydes with alkyl chains
between two formyl groups such as 2q and 2r [35]
123

R. Rashidi et al.
catalyst was recovered by simple filtration, rinsed with
acetone, dried, and then reused for the next run. The cat-
alyst could be cycled for at least six times without
noticeable loss of its activity (Table 4).
Scheme 3
A plausible mechanism for the formation of quinoxali-
nes in the presence of [PPy]HSO4@nSiO2 catalyst is
illustrated in Scheme 5. First, the carbonyl group is acti-
vated by the catalyst to afford A, which upon reaction with
1-(2-aminophenyl)pyrrol gives B. Then, elimination of
water from B in the presence of the catalyst affords C. Fi-
nally, acid catalyzed cyclization of C followed by
intramolecular hydrogen shift affords the desired product
and releases the catalyst for the next cycle.
Conclusion
To sum up, [PPy]HSO4@nSiO2 is prepared and used as a
catalyst for the convenient synthesis of substituted as well
as mono- and bis-4,5-dihydropyrrolo[1,2-a]quinoxalines.
In addition, 4-methyl-4,5-dihydropyrrolo[1,2-a]quinoxali-
nes were produced by the reaction of 1-(2-aminophe-
nyl)pyrrole with acetophenone derivatives. This method
presents advantages such as mild conditions, green solvent
(H2O), high yields, short reaction times, and a recyclable
acidic catalyst.
Scheme 4
Experimental
The chemicals used in this work were purchased from
Fluka and Merck chemical companies. The dialdehydes 2r
and 2q were prepared according to the reported procedure
[35]. Melting points were determined with a Stuart Sci-
entific SMP2 apparatus. FT-IR spectra were recorded on a
Nicolet-Impact 400D instrument in the range of
400–4000 cm-1 1H and 13C NMR spectra (400 and
.
100 MHz) were recorded on a Bruker Avance 400 MHz
spectrometer using CDCl3 solvent. Elemental analysis was
done on LECO, CHNS-932 analyzer. Scanning electron
microscopy field emission-scanning electron microscope
(FE-SEM) measurements were performed on a Hitachi
S-4700. The UV–Vis diffuse reflectance spectra of the
samples were recorded in
spectrophotometer.
a
JASCO V-670
Synthesis of propylpyridinium hydrogen sulfate
supported on silica nanoparticles
([PPy]HSO4@nSiO2)
Recyclability of the catalyst
The reusability and resumption of catalyst, which is
essential from the economic and environmental point of
views, was tested in the reaction of 1-(2-aminophe-
nyl)pyrrole and 4-nitrobenzaldehyde. In each cycle, the
A combination of 8.0 cm3 (3-chloropropyl)trimethoxysi-
lane (CPTMS) and 3.0 g activated nSiO2 [25] in 50.0 cm3
toluene (anhydrous) was refluxed for 24 h. The reaction
123

Highly selective synthesis of mono- and bis-4,5-dihydropyrrolo[1,2-a]quinoxalines catalyzed…
4-(4-Nitrophenyl)-4,5-dihydropyrrolo[1,2-a]quinoxaline
Table 3 Synthesis of 4-methyl-4,5-dihydropyrrolo[1,2-a]quinoxali-
nes 6
(3a)
Yield: 99% (288.28 mg); m.p.: 107–109 °C (106–108 °C
[18]).
4-(3-Nitrophenyl)-4,5-dihydropyrrolo[1,2-a]quinoxaline
(3b, C17H13N3O2)
Yield: 98% (285.38 mg); m.p.: 98–101 °C; FT-IR (KBr):
ꢀ
m = 3316, 3040, 2818, 1609, 1521, 1485, 1348, 1291, 1159,
1089, 919, 744 cm-1 1H NMR (400 MHz, CDCl3):
;
Entry
R
Product
Time/min
Yield/%a
d = 5.56 (dd, J = 2.4, 1.2 Hz, 1H, Ar-H), 5.68 (s, 1H, CH),
6.25 (t, J = 3.2 Hz, 1H, Ar-H), 6.80 (dd, J = 8.0, 1.2 Hz,
1H, Ar-H), 6.87 (td, J = 7.0, 1.2 Hz, 1H, Ar-H), 6.99 (td,
J = 7.0, 1.2 Hz, 1H, Ar-H), 7.22 (t, J = 1.4 Hz, 1H, Ar-H),
7.35 (d, J = 8.0 Hz, 1H, Ar-H), 7.50–7.58 (m, 2H, Ar-H),
7.79 (d, J = 7.6 Hz, 1H, Ar-H), 8.19 (dt, J = 8.0, 1.2 Hz,
1H, Ar-H), 8.35 (s, 1H, NH) ppm; 13C NMR (100 MHz,
CDCl3): d = 55.55, 106.30, 110.43, 113.88, 114.85, 115.53,
120.00, 122.89, 123.34, 124.02, 124.93, 128.33, 129.68,
130.76, 134.10, 135.29, 143.73 ppm.
1
2
3
4
4-NO2C6H4
4-ClC6H4
6a
6b
6c
6d
40
60
90
90
98
95
82
70
4-CyclohexylC6H4
4-MeC6H4
aIsolated yield
Table 4 Reusability of the [PPy]HSO4@nSiO2 catalyst in the syn-
thesis of 3a
Run
1
2
3
4
5
6
4-(2-Nitrophenyl)-4,5-dihydropyrrolo[1,2-a]quinoxaline
(3c, C17H13N3O2)
Yield/%a
99
98
95
93
93
91
Yield: 98% (285.43 mg); m.p.: 112–115 °C; FT-IR (KBr):
Reaction conditions: 1-(2-aminophenyl)pyrrol (1, 1.0 mmol), 4-ni-
trobenzaldehyde (2a, 1.0 mmol) and [PPy]HSO4@nSiO2 catalyst
(0.8 mol%), 70 °C
ꢀ
m = 3424, 3135, 3067, 2864, 1722, 1609, 1525, 1477, 1351,
1146, 1097, 752 cm-1 1H NMR (400 MHz, CDCl3):
;
aIsolated yield
d = 6.59 (dd, J = 4.0, 1.2 Hz, 1H, CH), 6.88 (dd, J = 4.0,
1.2 Hz, 1H, Ar-H), 7.50 (td, J = 7.8, 1.4 Hz, 1H, Ar-H), 7.60
(td, J = 7.2, 1.4 Hz, 1H, Ar-H), 7.67–7.72 (m, 1H, Ar-H),
7.77–7.78 (m, 3H, Ar-H), 7.93 (dd, J = 8.2, 1.2 Hz, 1H, Ar-
H), 8.00–8.04 (m, 3H, Ar-H), 8.18(s, 1H, NH) ppm;13C NMR
(100 MHz, CDCl3): d = 60.03, 107.29, 109.86, 113.88,
114.34, 115.13, 119.04, 124.81, 125.55, 128.18, 130.19,
130.26, 131.30, 133.27, 135.77, 141.18, 149.59 ppm.
mixture was separated by filtration and the CP-nSiO2 was
washed with toluene using a Soxhlet apparatus and dried at
100 °C. In continue, a mixture of 2 g CP-nSiO2 and
10.0 cm3 pyridine was refluxed for 120 h. The solid
material ([PPy]Cl@nSiO2) was filtered, washed (toluene
and ethanol), and then dried at 70 °C. Finally, a mixture of
2 g [PPy]Cl@nSiO2 and 2.74 g sodium hydrogen sulfate
(20 mmol) in 30.0 cm3 distilled water was reacted at 25 °C
for 12 h. The [PPy]HSO4@nSiO2 was separated, washed
with distilled water, and dried at 70 °C.
4-(4-Chlorophenyl)-4,5-dihydropyrrolo[1,2-a]quinoxaline
(3d)
Yield: 96% (269.48 mg); m.p.: 103–107 °C (105–107 °C
[15]).
4-(2,6-Dichlorophenyl)-4,5-dihydropyrrolo[1,2-a]quinoxa-
line (3e, C17H12Cl2N2)
Production of substituted 4,5-dihydropyrrolo[1,2-
a]quinoxaline derivatives
Yield: 97% (305.70 mg); m.p.: 137–139 °C; FT-IR (KBr):
ꢀ
m = 3312, 3134, 2829, 1720, 1609, 1588, 1513, 1463,
A mixture of 1-(2-aminophenyl)pyrrole (1.0 mmol), car-
bonyl compound (1.0 mmol), and 50 mg [PPy]HSO4@-
nSiO2 (0.8 mol%) in water was stirred at 70 °C. The
advancement of the reaction was checked by TLC (eluent:
petroleum ether-EtOAc, 10:1). At the end 10 cm3 EtOH
were added, the catalyst was separated by filtration and
washed with 10 cm3 EtOH. The filtrate containing the
crude product in a mixture of H2O and EtOH, was evap-
orated. The pure product was most often obtained without
any purification. If necessary, the product was recrystal-
lized from petroleum ether-EtOAc.
1332, 1291, 1154, 1045, 857, 747 cm-1 1H NMR
;
(400 MHz, CDCl3): d = 4.39 (s, 1H, NH), 5.84–5.85 (m,
1H, Ar-H), 6.06 (s, 1H, CH), 6.33 (t, J = 3.2 Hz, 1H, Ar-
H), 6.73 (dd, J = 7.8, 1.2 Hz, 1H, Ar-H), 6.87 (td, J = 7.6,
1.6 Hz, 1H, Ar-H), 6.97 (td, J = 7.6, 1.2 Hz, 1H, Ar-H),
7.12–7.17 (m, 2H, Ar-H), 7.26 (dd, J = 3.2, 1.6 Hz, 1H,
Ar-H), 7.37 (dd, J = 8.0, 1.2 Hz, 1H, Ar-H), 7.44 (d,
J = 2.0 Hz, 1H, Ar-H) ppm; 13C NMR (100 MHz,
CDCl3): d = 51.48, 106.13, 110.43, 114.62, 114.73,
115.72, 119.66, 120.74, 124.90, 126.88, 127.65, 129.29,
130.19, 133.25, 134.19, 134.84, 138.24 ppm.
123

R. Rashidi et al.
Scheme 5
4-(4-Methoxyphenyl)-4,5-dihydropyrrolo[1,2-a]quinoxa-
110.09, 114.05, 114.54, 115.70, 118.90, 123.26, 124.62,
125.49, 128.24, 128.89, 135.80, 157.57, 160.35 ppm.
line (3f)
Yield: 98% (270.83 mg); m.p.: 112–115 °C (108–110 °C
[18]).
4-Styryl-4,5-dihydropyrrolo[1,2-a]quinoxaline (3i)
Yield: 90% (245.08 mg); m.p.: 124–127 °C (125–126 °C
[14]).
4-(3-Methoxyphenyl)-4,5-dihydropyrrolo[1,2-a]quinoxa-
line (3g)
Yield: 97% (268.0 mg); m.p.: 127–131 °C (132–134 °C
[13]).
4-(Anthracen-10-yl)-4,5-dihydropyrrolo[1,2-a]quinoxaline
(3j, C25H18N2)
Yield: 95% (329.14 mg); m.p.: 160–164 °C; FT-IR (KBr):
ꢀ
4-(2,4-Dimethoxyphenyl)-4,5-dihydropyrrolo[1,2-
a]quinoxaline (3h, C19H18N2O2)
m = 3386, 3045, 2916, 1616, 1515, 1473, 1329, 1291,
1156, 1037, 729 cm-1 1H NMR (400 MHz, CDCl3):
;
Yield: 99% (303.28 mg); m.p.: 132–135 °C; FT-IR (KBr):
d = 4.16 (s, 1H, NH), 5.30 (s, 1H, CH), 6.17 (s, 1H, Ar-H),
6.71 (d, J = 7.6 Hz, 1H, Ar-H), 6.91 (t, J = 7.4 Hz, 1H,
Ar-H), 7.0 (t, J = 7.4 Hz, 1H, Ar-H), 7.16 (s, 1H, Ar-H),
7.39–7.49 (m, 6H, Ar-H), 8.00 (d, J = 8.0 Hz, 1H, Ar-H),
8.07 (d, J = 6.8 Hz, 1H, Ar-H), 8.33 (d, J = 6.8 Hz, 1H,
Ar-H), 8.52 (s, 1H, Ar-H), 8.76 (d, J = 8.8 Hz, 1H, Ar-H)
ppm; 13C NMR (100 MHz, CDCl3): d = 50.97, 106.30,
110.46, 114.17, 115.05, 115.33, 119.38, 122.63, 124.56,
124.76, 124.87, 125.07, 126.73, 128.10, 128.79, 129.19,
129.49, 129.81, 137.06 ppm.
ꢀ
m = 3352, 3127, 3002, 2933, 2830, 1875, 1611, 1510,
1479, 1337, 1285, 1206, 1156, 1034, 917, 832, 746 cm-1
;
1H NMR (400 MHz, CDCl3): d = 3.77 (s, 3H, CH3), 3.90
(s, 3H, CH3), 4.52 (s, 1H, NH), 5.90–5.91 (m, 1H, Ar-H),
5.96 (s, 1H, CH), 6.32–6.35 (m, 2H, Ar-H), 6.49 (d,
J = 2.4 Hz, 1H, Ar-H), 6.68 (dd, J = 7.6, 1.2 Hz, 1H, Ar-
H), 6.78–6.83 (m, 2H, Ar-H), 6.91 (td, J = 7.6, 1.2 Hz,
1H, Ar-H), 7.24 (dd, J = 2.8, 1.2 Hz, 1H, Ar-H), 7.34 (dd,
J = 8.0, 1.2 Hz, 1H, Ar-H) ppm; 13C NMR (100 MHz,
CDCl3): d = 48.87, 55.36, 55.53, 98.45, 104.03, 105.53,
123

Highly selective synthesis of mono- and bis-4,5-dihydropyrrolo[1,2-a]quinoxalines catalyzed…
4-(Thiophen-3-yl)-4,5-dihydropyrrolo[1,2-a]quinoxaline
(3k, C15H12N2S)
1479, 1338, 1295, 1182, 1093, 743 cm-1 1H NMR
;
(400 MHz, CDCl3): d = 0.91 (t, J = 4.4 Hz, 3H, CH3),
1.2–1.3 (m, 6H, CH2), 1.4–1.5 (m, 2H, CH2), 1.7–1.8 (m,
2H, CH2), 3.09 (t, J = 7.8 Hz, 1H, CH), 4.01 (s, 1H, NH),
5.99–6.00 (m, 1H, Ar-H), 6.31 (t, J = 3.2 Hz, 1H, Ar-H),
6.74 (dd, J = 7.6, 1.2 Hz, 1H, Ar-H), 6.80 (td, J = 7.6,
1.4 Hz, 1H, Ar-H), 6.95 (td, J = 7.6, 1.4 Hz, 1H, Ar-H),
7.15 (dd, J = 2.8, 1.2 Hz, 1H, Ar-H), 7.28 (dd, J = 7.6,
1.2 Hz, 1H, Ar-H) ppm; 13C NMR (100 MHz, CDCl3):
d = 14.16, 22.65, 25.60, 29.33, 31.83, 35.34, 51.08,
103.80, 109.92, 113.71, 114.11, 114.62, 115.36, 118.98,
124.59, 129.85, 135.97 ppm.
Yield: 98% (247.22 mg); m.p.: 102–105 °C; FT-IR (KBr):
mꢀ = 3426, 3357, 3138, 3066, 2927, 2785, 2696, 1761,
1
1605, 1513, 1497, 1330, 1278, 1148, 1037, 706 cm-1; H
NMR (400 MHz, CDCl3): d = 4.33 (s, 1H, NH), 5.85–5.86
(m, 1H, Ar-H), 5.92 (s, 1H, CH), 6.30 (t, J = 3.2 Hz, 1H,
Ar-H), 6.79 (dd, J = 7.8, 1.4 Hz, 1H, Ar-H), 6.89 (td,
J = 7.6, 1.4 Hz, 1H, Ar-H), 6.98–7.02 (m, 2H, Ar-H), 7.09
(dd, J = 3.4, 1.0 Hz, 1H, Ar-H), 7.21 (dd, J = 2.8, 1.6 Hz,
1H, Ar-H), 7.30 (dd, J = 5.0, 1.0 Hz, 1H, Ar-H), 7.35 (dd,
J = 8.0, 1.2 Hz, 1H, Ar-H) ppm; 13C NMR (100 MHz,
CDCl3): d = 51.59, 105.87, 110.26, 113.63, 114.54,
114.79, 115.75, 119.86, 124.76, 125.49, 125.72, 126.48,
129.15, 135.32, 145.43 ppm.
Selective synthesis of mono- and bis-4,5-dihydropy-
rrolo[1,2-a]quinoxalines A mixture of 1-(2-aminophe-
nyl)pyrrole (1 or 2 mmol), dialdehyde (1 mmol) and
[PPy]HSO4@nSiO2 (0.8 mol%) was stirred at 70 °C for
the appropriate time according to Schemes 3 and 4. The
workup was carried out as mentioned for preparation of
4,5-dihydropyrrolo[1,2-a]quinoxalines. The pure product
was obtained by recrystallization from EtOAc or column
chromatography (eluent: petroleum ether-EtOAc, 10:1).
4-(1H-Indol-3-yl)-4,5-dihydropyrrolo[1,2-a]quinoxaline
(3l, C19H15N3)
Yield: 85% (242.50 mg); m.p.: 178–182 °C; FT-IR (KBr):
ꢀ
m = 3396, 3130, 3046, 2923, 2887, 1770, 1607, 1513,
1
1437, 1332, 1237, 1152, 1098, 911, 743 cm-1; H NMR
(400 MHz, CDCl3): d = 4.19 (s, 1H, NH), 5.73–5.74 (m,
1H, Ar-H), 5.92 (s, 1H, CH), 6.25 (t, J = 3.2 Hz, 1H, Ar-
H), 6.73 (dd, J = 7.6, 1.2 Hz, 1H, Ar-H), 6.85 (td, J = 7.6,
1.2 Hz, 1H, Ar-H), 6.96 (td, J = 7.6, 1.2 Hz, 1H, Ar-H),
7.09 (td, J = 7.6, 0.8 Hz, 1H, Ar-H), 7.19–7.25 (m, 2H,
Ar-H), 7.36 (dd, J = 8.0, 1.2 Hz, 1H, Ar-H), 7.40 (d,
J = 8.0 Hz, 1H, Ar-H), 7.49–7.53 (m, 2H, Ar-H), 8.15 (s,
1H, NH indole) ppm; 13C NMR (100 MHz, CDCl3):
d = 48.82, 105.39, 110.12, 111.36, 113.71, 114.25, 114.79,
115.53, 119.35, 119.80, 121.30, 122.01, 122.41, 123.17,
124.62, 125.47, 126.94, 129.85, 136.56 ppm.
4-(4,5-Dihydropyrrolo[1,2-a]quinoxalin-4-yl)benzalde-
hyde (3o, C18H14N2O)
Yield: 97% (266.03 mg); m.p.: 115–119 °C; FT-IR (KBr):
ꢀ
m = 3343, 3115, 3057, 2923, 2799, 1692, 1513, 1487,
1
1332, 1286, 1158, 1067, 915, 835, 751 cm-1; H NMR
(400 MHz, CDCl3): d = 4.24 (s, 1H, NH), 5.58–5.59 (m,
1H, Ar-H), 5.65 (s, 1H, CH), 6.26 (t, J = 3.2 Hz, 1H, Ar-
H), 6.78 (dd, J = 7.8, 1.4 Hz, 1H, Ar-H), 6.88 (td, J = 7.6,
1.4 Hz, 1H, Ar-H), 6.99 (td, J = 7.6, 1.2 Hz, 1H, Ar-H),
7.22 (dd, J = 2.8, 1.4, 1H, Ar-H), 7.35 (dd, J = 7.6,
1.2 Hz, 1H, Ar-H), 7.63 (d, J = 8.0 Hz, 2H, Ar-H), 7.88
(dd, J = 6.4, 1.6 Hz, 2H, Ar-H), 10.02 (s, 1H, CHO) ppm;
13C NMR (100 MHz, CDCl3): d = 55.89, 106.13, 110.37,
114.68, 114.85, 115.50, 119.77, 124.90, 128.47, 130.19,
135.54, 136.31, 148.29, 191.92 ppm.
6-Chloro-3-(4,5-dihydropyrrolo[1,2-a]quinoxalin-4-yl)-
4H-chromen-4-one (3m, C20H13ClN2O2)
Yield: 98% (341.86 mg); m.p.: 169–172 °C; FT-IR (KBr):
ꢀ
m = 3334, 3133, 3059, 2925, 2857, 1914, 1639, 1515,
1
1464, 1311, 1289, 1136, 1049, 827, 753 cm-1; H NMR
(400 MHz, CDCl3): d = 5.25 (s, 1H, NH), 5.92 (s, 1H,
CH), 6.13 (dd, J = 3.4, 1.4 Hz, 1H, Ar-H), 6.40 (t,
J = 3.2 Hz, 1H, Ar-H), 6.70 (dd, J = 7.8, 1.4 Hz, 1H, Ar-
H), 6.81 (td, J = 7.6, 1.2 Hz, 1H, Ar-H), 6.92 (td, J = 7.4,
1.4 Hz, 1H, Ar-H), 7.15 (d, J = 1.2 Hz, 1H, Ar-H),
7.32–7.35 (m, 3H, Ar-H), 7.59 (dd, J = 8.8, 2.4 Hz, 1H,
Ar-H), 8.20 (d, J = 2.8 Hz, 1H, Ar-H) ppm; 13C NMR
(100 MHz, CDCl3): d = 47.80, 106.15, 109.92, 110.40,
114.65, 114.96, 115.75, 116.32, 119.04, 119.38, 119.97,
123.82, 124.67, 125.10, 131.27, 134.16, 134.36, 154.43,
154.74, 176.60 ppm.
3-(4,5-Dihydropyrrolo[1,2-a]quinoxalin-4-yl)benzalde-
hyde (3p, C18H14N2O)
Yield: 91% (249.61 mg); m.p.: 110–113 °C; FT-IR (KBr):
ꢀ
m = 3345, 3133, 3059, 2809, 2780, 1910, 1694, 1514,
1
1477, 1335, 1287, 1140, 746 cm-1; H NMR (400 MHz,
CDCl3): d = 5.65 (s, 1H, NH), 6.27 (t, J = 3.2 Hz, 1H,
CH), 6.79 (d, J = 8.0 Hz, 1H, Ar-H), 7.23 (d,
J = 1.2 Hz, 1H, Ar-H), 7.33–7.41 (m, 3H, Ar-H),
7.46–7.60 (m, 4H, Ar-H), 7.91 (dd, J = 10.4, 7.6 Hz, 1H,
Ar-H), 8.02 (s, 1H, Ar-H), 10.03 (s, 1H, CHO) ppm; 13C
NMR (100 MHz, CDCl3): d = 55.89, 105.92, 106.08,
108.55, 110.43, 113.78, 114.95, 115.54, 119.43, 119.72,
124.91, 125.53, 128.00, 129.51, 130.55, 134.11, 134.53,
192.17 ppm.
4-Hexyl-4,5-dihydropyrrolo[1,2-a]quinoxaline
(3n, C17H22N2)
ꢀ
Oil. Yield: 85% (216.20 mg); FT-IR (KBr): m = 3354,
3103, 3061, 2927, 2856, 2671, 1910, 1722, 1611, 1515,
123

R. Rashidi et al.
2-[4-[2-(4,5-Dihydropyrrolo[1,2-a]quinoxalin-4-yl)phe-
13C NMR (100 MHz, CDCl3): d = 56.09, 105.90, 110.20,
113.71, 114.14, 114.43, 114.76, 115.40, 119.44, 124.70,
127.84, 128.64, 129.06, 136.14, 141.92 ppm.
noxy]butoxy]benzaldehyde (3q, C28H26N2O3)
ꢀ
Oil. Yield: 78% (342.07 mg); FT-IR (KBr): m = 3354, 3137,
3067, 2947, 2873, 2758, 2247, 1914, 1685, 1515, 1451, 1338,
1240, 1160, 1043, 753 cm-1; 1H NMR (400 MHz, CDCl3):
d = 0.95 (dd, J = 6.4, 2.8 Hz, 2H, CH2), 1.33 (dd, J = 8.0,
7.2 Hz, 2H, CH2), 4.15 (t, J = 6.0 Hz, 4H, CH2), 4.56 (s, 1H,
NH), 5.91 (d, J = 3.2 Hz, 1H, Ar-H), 6.08 (s, 1H, CH), 6.36
(t, J = 3.0 Hz, 1H, Ar-H), 6.60–6.70 (m, 1H, Ar-H),
6.80–6.9 (m, 6H, Ar-H), 7.0–7.1 (m, 2H, Ar-H), 7.20 (d,
J = 8.0 Hz, 1H, Ar-H), 7.34 (dd, J = 7.6, 4.8 Hz, 1H, Ar-
H), 7.49–7.59 (m, 1H, Ar-H), 7.86–7.89 (m, 1H, Ar-H),
10.55 (s, 1H, CHO) ppm; 13C NMR (100 MHz, CDCl3):
d = 25.46, 25.63, 48.93, 67.40, 67.50, 105.28, 109.70,
110.70, 111.97, 113.62, 114.06, 114.10, 115.08, 118.49,
120.22, 120.30, 120.39, 124.17, 127.83, 127.94, 128.03,
128.35, 128.39, 129.56, 130.21, 135.57, 155.38,
189.12 ppm.
1,4-Bis[2-(4,5-dihydropyrrolo[1,2-a]quinoxalin-4-yl)phe-
noxy]butane (4q, C38H34N4O2)
ꢀ
Oil. Yield: 81% (468.73 mg); FT-IR (KBr): m = 3349,
3136, 3061, 2947, 2872, 1916, 1684, 1515, 1484, 1336,
1
1238, 1047, 975, 746 cm-1; H NMR (400 MHz, CDCl3):
d = 2.08 (t, J = 2.8 Hz, 4H, CH2), 4.14–4.20 (m, 4H,
CH2), 4.49 (s, 2H, NH), 5.85–5.88 (m, 2H, CH), 6.04 (s,
2H, Ar-H), 6.33 (t, J = 3.2 Hz, 2H, Ar-H), 6.60 (dd,
J = 4.0, 1.2 Hz, 2H, Ar-H), 6.61 (dd, J = 4.2, 1.4 Hz, 2H,
Ar-H), 6.79–6.90 (m, 8H, Ar-H), 6.99 (dt, J = 7.6, 1.8 Hz,
2H, Ar-H), 7.23–7.24 (m, 2H, Ar-H), 7.34 (m, Hz, 2H, Ar-
H) ppm; 13C NMR (100 MHz, CDCl3): d = 26.05, 48.99,
67.33, 105.45, 109.81, 110.83, 113.71, 114.17, 115.19,
118.53, 120.45, 124.25, 124.93, 127.59, 127.93, 128.44,
130.31, 135.40, 155.45 ppm.
2-[6-[2-(4,5-Dihydropyrrolo[1,2-a]quinoxalin-4-yl)phe-
1,6-Bis[2-(4,5-dihydropyrrolo[1,2-a]quinoxalin-4-yl)phe-
noxy]hexyloxy]benzaldehyde (3r, C30H30N2O3)
noxy]hexane (4r, C40H38N4O2)
ꢀ
Oil. Yield: 90% (419.90 mg); FT-IR (KBr): m = 3347,
3133, 3070, 2938, 2861, 2758, 2248, 1914, 1736, 1685,
ꢀ
Oil. Yield: 86% (521.84 mg); FT-IR (KBr): m = 3384,
3137, 3061, 2927, 2856, 2242, 1717, 1613, 1515, 1489,
1599, 1455, 1371, 1241, 1161, 1007, 910, 754 cm-1; H
1
;
1337, 1234, 1101, 1047, 908, 737 cm-1 1H NMR
NMR (400 MHz, CDCl3): d = 1.61 (t, J = 3.4 Hz, 4H,
CH2), 1.90 (t, J = 4.4 Hz, 4H, CH2), 4.05–4.14 (m, 4H,
CH2), 4.61 (s, 1H, NH), 5.91 (d, J = 1.6 Hz, 1H, Ar-H),
6.05 (s, 1H, CH), 6.34 (t, J = 3.0 Hz, 1H, Ar-H), 6.66 (dd,
J = 8.0, 1.2 Hz, 1H, Ar-H), 6.77–6.82 (m, 2H, Ar-H),
6.86–6.92 (m, 2H, Ar-H), 6.94–7.04 (m, 3H, Ar-H), 7.20
(d, J = 7.6 Hz, 1H, Ar-H), 7.33 (d, J = 8.0 Hz, 1H, Ar-
H), 7.49–7.57 (m, 2H, Ar-H), 7.85 (dd, J = 7.6, 1.2 Hz,
1H, Ar-H), 10.54 (s, 1H, CHO) ppm; 13C NMR (100 MHz,
CDCl3): d = 25.36, 25.59, 28.56, 28.83, 48.98, 67.78,
67.81 105.26, 109.62, 110.64, 112.01, 112.02, 112.34,
113.24, 113.57, 114.04, 115.06, 118.41, 120.09, 124.09,
124.74, 127.67, 127.69, 127.78, 127.80, 128.26, 130.10,
135.50, 155.44, 189.33 ppm.
(400 MHz, CDCl3): d = 1.64 (t, J = 3.4 Hz, 4H, CH2),
1.91 (t, J = 6.2 Hz, 4H, CH2), 4.03–4.14 (m, 4H, CH2),
4.57 (s, 2H, NH), 5.91 (s, 2H, CH), 6.05 (d, J = 2.0 Hz,
2H, Ar-H), 6.34 (t, J = 3.0 Hz, 2H, Ar-H), 6.63 (d,
J = 7.6 Hz, 2H, Ar-H), 6.80–6.90 (m, 6H, Ar-H),
6.87–6.93 (m, 6H, Ar-H), 7.19 (td, J = 8.0, 1.6 Hz, 2H,
Ar-H), 7.24 (s, 2H, Ar-H), 7.33 (d, J = 7.6 Hz, 2H, Ar-H)
ppm; 13C NMR (100 MHz, CDCl3): d = 26.05, 29.22,
49.61, 68.18, 105.79, 110.15, 111.17, 112.53, 114.11,
114.56, 115.58, 118.92, 120.62, 124.64, 128.21, 128.83,
130.70, 136.03, 155.96, 161.45 ppm.
4-Methyl-4-(4-nitrophenyl)-4,5-dihydropyrrolo[1,2-
a]quinoxaline (6a, C18H15N3O2)
Yield: 98% (299.20 mg); m.p.: 231–233 °C; FT-IR (KBr):
1,4-Bis(4,5-dihydropyrrolo[1,2-a]quinoxalin-4-yl)benzene
ꢀ
m = 3342, 2969, 1726, 1512, 1481, 1343, 1189, 1083,
(4o)
Yield: 90% (373.01 mg); m.p.: 217–220 °C (219–220 °C
[14]).
1
744 cm-1; H NMR (400 MHz, CDCl3): d = 1.95 (s, 3H,
CH3), 4.44 (s, 1H, NH), 6.16 (dd, J = 3.4, 1.4 Hz, 1H, Ar-
H), 6.39 (t, J = 3.2 Hz, 1H, Ar-H), 6.82–6.88 (m, 2H, Ar-
H), 6.99 (td, J = 8.0, 1.6 Hz, 1H, Ar-H), 7.21 (dd, J = 2.8,
1.6 Hz, 1H, Ar-H), 7.28 (dd, J = 8.0, 1.0 Hz, 1H, Ar-H),
7.43–7.47 (m, 2H, Ar-H), 8.07–8.11 (m, 2H, Ar-H) ppm;
13C NMR (100 MHz, CDCl3): d = 28.99, 56.97, 104.88,
110.32, 114.85, 114.99, 116.09, 120.06, 123.57, 125.64,
125.72, 126.74, 131.50, 134.33, 146.79, 153.92 ppm.
1,3-Bis(4,5-dihydropyrrolo[1,2-a]quinoxalin-4-yl)benzene
(4p, C28H22N4)
Yield: 85% (352.37 mg); m.p.: 186–189 °C; FT-IR (KBr):
ꢀ
m = 3349, 3100, 2923, 1907, 1606, 1515, 1475, 1337,
1283, 1143, 1095, 927, 806, 750 cm-1
;
1H NMR
(400 MHz, CDCl3): d = 5.65 (s, 2H, NH), 6.27 (t,
J = 3.2 Hz, 2H, CH), 6.88 (dd, J = 5.6, 1.8 Hz, 2H, Ar-
H), 6.99–7.03 (m, 2H, Ar-H), 7.22 (dd, J = 8.8, 1.2 Hz,
2H, Ar-H), 7.33–7.44 (m, 4H, Ar-H), 7.48–7.51 (m, 3H,
Ar-H), 7.53–7.58 (m, 6H, Ar-H), 8.02 (s, 2H, Ar-H) ppm;
4-(4-Chlorophenyl)-4-methyl-4,5-dihydropyrrolo[1,2-
a]quinoxaline (6b, C18H15ClN2)
Yield: 95% (280.01 mg); m.p.: 171–174 °C; FT-IR (KBr):
ꢀ
m = 3349, 2977, 1613, 1511, 1480, 1333, 1188, 1088,
123

Highly selective synthesis of mono- and bis-4,5-dihydropyrrolo[1,2-a]quinoxalines catalyzed…
747 cm-1; H NMR (400 MHz, CDCl3): d = 1.90 (s, 3H,
CH3), 4.22 (s, 1H, NH), 6.07 (dd, J = 3.2, 1.6 Hz, 1H, Ar-
H), 6.35–6.37 (m, 2H, Ar-H), 6.79 (dd, J = 8.0, 1.2 Hz,
1H, Ar-H), 6.83 (dd, J = 7.6, 1.2 Hz, 1H, Ar-H), 6.87 (t,
J = 2.0 Hz,1H, Ar-H), 6.97 (td, J = 7.8, 1.4 Hz, 1H, Ar-
H), 7.19 (dd, J = 3.0, 1.4 Hz, 2H, Ar-H), 7.27–7.29 (m,
2H, Ar-H) ppm; 13C NMR (100 MHz, CDCl3): d = 29.16,
56.63, 104.60, 109.41, 110.09, 114.51, 114.73, 115.95,
118.41, 119.60, 121.70, 124.84, 127.28, 128.35, 134.81,
144.92 ppm.
1
ˆ
3. Pereira JA, Pessoa AM, Cordeiro MND, Fernandes R, Prudencio
C, Noronha JP, Vieira M (2015) Eur J Med Chem 97:664
4. Vessally E (2016) RSC Adv 6:18619
´
´
5. Estevez V, Villacampa M, Menendez JC (2014) Chem Soc Rev
43:4633
6. Wang Y, Cui L, Wang Y, Zhou Z (2016) Tetrahedron Asym-
metry 27:85
7. Mamedov VA, Kalinin AA (2010) Chem Heterocycl Compd
46:641
8. Xu H, Fan LL (2011) Eur J Med Chem 46:1919
9. Fan LL, Huang N, Yang RG, He S-Z, Yang L-M, Xu H, Zheng
Y-T (2012) Lett Drug Des Disc 9:44
10. Sabatucci JP, Ye F, Mahaney PE (2006) Preparation of [pyr-
rolo[1,2-a]quinoxalin-5(4H)-yl]sulfonyls and carbonyls and their
use as estrogenic agents. Patent WO 2006068928, Jun 29, 2006.
Chem Abstr 145:103721
4-(4-Cyclohexylphenyl)-4-methyl-4,5-dihydropyrrolo[1,2-
a]quinoxaline (6c, C24H26N2)
Yield: 82% (280.80 mg); m.p.: 168–170 °C; FT-IR (KBr):
11. Pictet A, Spengler T (1911) Ber Dtsch Chem Ges 44:2030
12. Strittmatter SM, Gunther E (2009) Nogo receptor binding small
molecules to promote axonal growth. Patent WO 2009073141,
Jun 11, 2009. Chem Abstr 151:49367
ꢀ
m = 3370, 2924, 1611, 1513, 1479, 1332, 1184, 1072,
1
742 cm-1; H NMR (400 MHz, CDCl3): d = 1.32–1.49
(m, 10 H, CH2), 1.91 (s, 3H, CH3), 2.45 (dd, J = 8.0,
1.2 Hz, 1H, CH), 3.67 (s, 1H, NH), 6.05 (dd, J = 3.4,
1.4 Hz, 1H, Ar-H), 6.35 (t, J = 3.2 Hz, 1H, Ar-H), 6.97
(td, J = 7.6, 1.2 Hz, 1H, Ar-H), 7.10 (d, J = 8.4 Hz, 2H,
Ar-H), 7.25 (dt, J = 6.4, 2.0 Hz, 2H, Ar-H), 7.33 (d,
J = 8.4 Hz, 2H, Ar-H), 7.93 (dt, J = 6.4, 2.0 Hz, 2H, Ar-
H) ppm; 13C NMR (100 MHz, CDCl3): d = 26.28, 27.18,
29.67, 34.43, 44.17, 56.86, 104.65, 109.41, 109.98, 114.62,
116.09, 118.41, 119.09, 121.70, 124.70, 125.61, 126.63,
127.19, 128.55, 142.09 ppm.
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Yield: 70% (192.00 mg); m.p.: 172–175 °C; FT-IR (KBr):
ꢀ
m = 3355, 2917, 1608, 1515, 1479, 1334, 1148, 1033,
1
743 cm-1; H NMR (400 MHz, CDCl3): d = 1.90 (s, 3H,
CH3), 2.17 (s, 3H, CH3), 3.80 (s, 1H, NH), 6.01 (dd,
J = 3.2, 1.6 Hz, 1H, Ar-H), 6.06 (dd, J = 3.8, 1.6 Hz, 1H,
Ar-H), 6.17 (br s, 1H, Ar-H), 6.26 (t, J = 3.0 Hz, 1H, Ar-
H), 6.32 (t, J = 3.2 Hz, 1H, Ar-H), 6.69 (dd, J = 7.6,
1.2 Hz, 1H, Ar-H), 7.15 (dd, J = 3.2, 1.6 Hz, 2H, Ar-H),
7.33 (m, 3H, Ar-H) ppm; 13C NMR (100 MHz, CDCl3):
d = 20.90, 29.39, 51.19, 109.41, 109.92, 114.25, 114.68,
116.15, 118.41, 119.21, 121.70, 124.64, 125.66, 127.19,
128.61, 128.89, 142.09 ppm.
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Acknowledgements The authors are grateful to the Research
Council of the University of Isfahan for the financial support of this
work.
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