An efficient four-component domino protocol for the rapid and green synthesis of functionalized benzo[a]pyrano[2,3-c]phenazine derivatives using caffeine as a homogeneous catalyst

Article abstract of DOI:10.1007/s11164-015-2083-5

A one-pot, two-step procedure has been used to synthesize functionalized benzo[a]pyrano[2,3-c]phenazine derivatives from a four-component condensation reaction of 2-hydroxynaphthalene-1,4-dione, o-phenylenediamine, aldehydes, and malononitrile in the pres

Full text of DOI:10.1007/s11164-015-2083-5

Res Chem Intermed
DOI 10.1007/s11164-015-2083-5
An efficient four-component domino protocol
for the rapid and green synthesis of functionalized
benzo[a]pyrano[2,3-c]phenazine derivatives using
caffeine as a homogeneous catalyst
Afshin Yazdani Elah Abadi1 Malek-Taher Maghsoodlou1
•
•
Reza Heydari1 Razieh Mohebat2
•
Received: 4 April 2015 / Accepted: 28 April 2015
Ó Springer Science+Business Media Dordrecht 2015
Abstract A one-pot, two-step procedure has been used to synthesize functional-
ized benzo[a]pyrano[2,3-c]phenazine derivatives from a four-component conden-
sation reaction of 2-hydroxynaphthalene-1,4-dione, o-phenylenediamine, aldehydes,
and malononitrile in the presence of 1,3,7-trimethylpurine-2,6-dione (caffeine) as an
expedient and reusable solid base catalyst. This new procedure has the following
advantages: operational simplicity, short reaction times, environmentally friendly,
easy work-up, and all the products were obtained in excellent yields.
Keywords Multi-component reactions (MCRs) Á One-pot synthesis Á
1,3,7-Trimethylpurine-2,6-dione (caffeine) Á 2-Hydroxynaphthalene-1,4-dione Á
o-Phenylenediamine Á Benzo[a]pyrano[2,3-c]phenazine
Introduction
Multi-component reactions (MCRs) are useful for the synthesis of various groups of
compounds [1–7], especially the synthesis of biologically important compounds,
because they provide an appropriate method for the preparation of new chemical
entities required by pharmaceutical and agrochemical industries [8, 9]. Therefore, in
the last few years, MCRs were developed as a fast and convenient way for efficient
synthesis of organic compounds [10–17].
Phenazine compounds are nitrogen-containing heterocycles that are found in
natural and synthetic products [18–24] showing a diversity of biological functions,
&
Malek-Taher Maghsoodlou
mt_maghsoodlou@yahoo.com; mt_maghsoodlou@chem.usb.ac.ir
1
2
Department of Chemistry, Faculty of Science, University of Sistan and Baluchistan,
P. O. Box 98135-674, Zahedan, Iran
Department of Chemistry, Islamic Azad University, Yazd Branch, P. O. Box 89195-155, Yazd,
Iran
123

A. Y. E. Abadi et al.
including antimalarial [25, 26], trypanocidal [27], fungicidal [28, 29], antiplatelet
[30], and antitumor [31] activities. Benzo[a]phenazines that have been formed from
a naphthoquinone and phenazin show high activity as dual inhibitors of topoiso-
merase I and II and are useful as antitumor agents [32]. In addition, chromenes have
shown remarkable effects as pharmaceuticals [33, 34], including antifungal [35, 36]
and antimicrobial activities [37]. Moieties of molecules with phenazines [24] and
chromenes [38] have attracted great attention in drug discovery. Functionalized
benzo[a]pyrano[2,3-c]phenazine derivatives have these moieties. We herein report a
very green synthesis of functionalized benzo[a]pyrano[2,3-c]phenazine derivatives
catalyzed by caffeine (Scheme 1; Fig. 1).
Experimental
General
All melting points were determined on an Electrothermal 9100 apparatus and are
uncorrected. IR spectra were recorded on a Shimadzu IR-470 spectrometer. Mass
spectra were recorded on a FINNIGAN-MAT 8430 mass spectrometer operating at
1
an ionization potential of 70 eV. The H nuclear magnetic resonance (NMR) and
13C NMR spectra were recorded on Bruker DRX-400 Avance instruments with
dimethyl sulfoxide (DMSO) as solvent. Thin-layer chromatography (TLC) was
performed on silica-gel Polygram SILG/UV 254 plates. All reagents were purchased
from Merck and Aldrich and used without further purification.
Scheme 1 Synthesis of 3-amino-2-cyano-1-aryl-1H-benzo[a]pyrano[2,3-c]phenazines derivatives
123

An efficient four-component domino protocol for the rapid…
Fig. 1 The structure of caffeine
General procedure for the synthesis of benzo[a]pyrano[2,3-c]phenazine
derivatives using the conventional heating method (method A)
At first, 2-hydroxynaphthalene-1,4-dione 1 (1 mmol) and o-phenylenediamine 2
(1 mmol) were mixed at 75 °C (solvent free) for \5 min until an orange solid of
benzo[a]phenazine 3 was formed. Then, aryl aldehydes 4 (1 mmol), and
malononitrile 5 (1 mmol), and caffeine (30 mol %) were added, the flask was
fitted with a condenser, and the resulting mixture in ethanol (10 mL) was heated to
reflux under stirring. The reaction was monitored by TLC, and after the required
time and completion of the reaction, the reaction mixture was cooled to room
temperature. The resulting solid product was filtered and was washed twice with
water (2 9 5 mL), then dried and subsequently recrystallized from hot ethanol. In
order to recover the catalyst, since caffeine is soluble in water, the water including
caffeine was evaporated under reduced pressure and caffeine was recovered and
reused.
General procedure for the synthesis of benzo[a]pyrano[2,3-c]phenazine
derivatives using the microwave heating method (method B)
In this method, at first, accordance with the procedures A, made an orange solid of
benzo[a]phenazine 3. Then, aryl aldehydes 4 (1 mmol), malononitrile 5 (1 mmol),
and caffeine (20 mol %) were added and this mixture was transferred to a
microwave oven and irradiated under 180 W. The reaction was monitored by TLC,
and upon completion, the reaction mixture was allowed to cool to room
temperature. Then, 5 mL of water was added to the mixture. The caffeine was
dissolved in water, and filtered for separation of the crude product. The separated
product was washed twice with water (2 9 5 mL). The solid crude product
subsequently recrystallized from hot ethanol to give the pure solid. Finally, the
water including caffeine was evaporated under reduced pressure and caffeine was
recovered and reused.
The analytical and spectroscopic data for the unknown compounds are as
follows:
3-Amino-2-cyano-1-(2,4-dichlorophenyl)-1H-benzo[a]pyrano[2,3-c]phenazine
(Table 2, entry 1): yield of method A: 0.435 g (93 %), method B: 0.444 g (95 %),
brown solid, m.p.: 308–310 °C; IR (KBr): mmax = 3457, 3376, 3170, 2185, 1653,
1620, 1589, 1492, 1464, 1401, 1390, 1347, 1326, 1288, 1220, 1160, 1097, 1050,
1
843, 753 cm-1; H NMR (400 MHz, DMSO-d6): d = 9.18 (d, 1H, J = 7.2 Hz,
123

A. Y. E. Abadi et al.
Ar–H), 8.41 (d, 1H, J = 7.6 Hz, Ar–H), 8.23–8.20 (m, 1H, Ar–H), 8.02–7.98 (m,
1H, Ar–H), 7.96–7.90 (m, 2H, Ar–H), 7.90–7.88 (m, 2H, Ar–H), 7.55 (d, 1H,
J = 2 Hz, Ar–H), 7.40 (s, 2H, NH2), 7.20 (d, 1H, J = 8.8, Ar–H), 7.15 (dd, 1H,
J1 = 2 Hz, J2 = 8.4 Hz, Ar–H), 5.83 (s, 1H, CH) ppm; 13C NMR (100 MHz,
DMSO-d6): d = 159.8, 147.0, 142.5, 141.9, 140.9, 140.5, 140.1, 133.7, 132.0,
131.9, 131.2, 131.0, 130.7, 130.6, 129.7, 129.5, 128.9, 128.8, 128.1, 125.9, 125.2,
122.6, 119.9, 112.6, 56.8, 34.6 ppm; MS (m/z, %): 468 (M?, 6).
3-Amino-2-cyano-1-(3-methoxyphenyl)-1H-benzo[a]pyrano[2,3-c]phenazine
(Table 2, entry 2): yield of method A: 0.374 g (87 %), method B: 0.387 g (90 %),
yellow solid, m.p.: 240–242 °C; IR (KBr): mmax = 3449, 3300, 3165, 2175, 1663,
1599, 1595, 1485, 1449, 1428, 1398, 1385, 1347, 1314, 1288, 1261, 1163, 1103, 1048,
1025, 992, 947, 871, 752 cm-1; 1H NMR (400 MHz, DMSO-d6): d = 9.16 (d, 1H,
J = 8 Hz, Ar–H), 8.40 (d, 1H, J = 8 Hz, Ar–H), 8.23–8.21 (m, 1H, Ar–H), 8.13–8.10
(m, 1H, Ar–H), 7.98–7.93 (m, 1H, Ar–H), 7.91–7.88 (m, 3H, Ar–H), 7.39 (s, 2H, NH2),
7.12 (t, 1H, J = 8 Hz, Ar–H), 7.00 (t, 1H, J = 2 Hz, Ar–H), 6.90 (d, 1H, J = 8 Hz,
Ar–H), 6.67 (dd, 1H, J1 = 2 Hz, J2 = 7.6 Hz, Ar–H), 5.43 (s, 1H, CH), 3.67 (s, 3H,
OCH3) ppm; 13C NMR (100 MHz, DMSO-d6): d = 160.4, 159.5, 147.2, 146.5, 141.9,
141.0, 140.4, 140.1, 131.2, 130.9, 130.6, 130.3, 129.9, 129.5, 129.4, 129.1, 126.0,
125.2, 122.5, 120.7, 120.1, 114.3, 114.2, 111.9, 58.2, 55.3, 37.7 ppm; MS (m/z, %):
430 (M?, 33).
Results and discussion
First, to find optimization conditions, the one-pot four-component reaction of
2-hydroxynaphthalene-1,4-dione, o-phenylenediamine, 2,4-dichlorobenzaldehyde,
and malononitrile in the presence of caffeine as catalyst was selected as model. So,
2-hydroxynaphthalene-1,4-dione (1 mmol) and o-phenylenediamine (1 mmol) were
mixed at 75 °C for\5 min until an orange solid of benzo[a]phenazine was formed
without using any catalyst under solvent-free conditions. Then, in method A, 2,4-
dichlorobenzaldehyde (1 mmol), malononitrile (1 mmol), and caffeine as catalyst
were added, the flask was fitted with a condenser, and the resulting mixture in
ethanol (10 mL) was heated to reflux under stirring. The use of different amounts of
catalyst (20, 25, 30, 35 mol %) at different temperatures (25, 50, 75 °C) were
investigated (Table 1). The best result was obtained with 30 mol % of caffeine as
catalyst at 75 °C in ethanol under reflux conditions and afforded 3-amino-2-cyano-
1-(2,4-dichlorophenyl)-1H-benzo[a]pyrano[2,3-c]phenazine in 30 min with 93 % of
yield.
Then, optimization conditions for method B, the same as above model using
different amounts of catalyst (10, 20, 30 mol %) at various powers (100, 180,
300 W) was investigated (Table 1). The best result was obtained with 20 mol % of
caffeine as catalyst at 180 W afforded 3-amino-2-cyano-1-(2,4-dichlorophenyl)-1H-
benzo[a]pyrano[2,3-c]phenazine in 7 min with 95 % of yield.
Using these optimized reaction conditions, the scope and efficiency of the
reaction were explored for the synthesis of a wide variety of substituted
benzo[a]pyrano[2,3-c]phenazine derivatives. The results are summarized in
123

An efficient four-component domino protocol for the rapid…
Table 1 Optimization of the reaction conditions for the synthesis of 3-amino-2-cyano-1-(2,4-dichlor-
ophenyl)-1H-benzo[a]pyrano[2,3-c]phenazine from 2-hydroxynaphthalene-1,4-dione, o-phenylenedi-
amine, 2,4-dichlorobenzaldehyde, and malononitrile in the presence of different amount of caffeine as
catalyst in varieties temperature and power
Entry
Conventional heating (method A)
Microwave irradiation (method B)
Cat
(mol %)
T (°C)
Time
(min)
Yield
(%)
Cat
(mol %)
Power
(W)
Time
(min)
Yield
(%)
1
2
3
4
5
6
7
20
20
30
25
30
35
30
25
50
50
50
75
50
75
60
60
45
45
30
45
20
Trace
85
10
20
30
30
20
10
20
100
180
180
180
180
180
300
10
10
10
7
Trace
95
92
94
87
94
93
7
95
93
7
82
90
5
91
Table 2 Synthesis of 3-amino-2-cyano-1-aryl-1H-benzo[a]pyrano[2,3-c]phenazine derivatives from the
reaction of 2-hydroxynaphthalene-1,4-dione, o-phenylenediamine, malononitrile, and aldehydes in the
presence of caffeine as catalyst
Entry
Aldehydes
Method A
(cat. 30 mol %),
(T. 75 °C)
Method B
(cat. 20 mol %),
(power. 180 W)
Melting point m.p.
(°C)/Lit. m.p. (°C)
[References]
Time
(min)
Yield
(%)
Time
(min)
Yield
(%)
1
2,4-(Cl)2C6H3
3-CH3OC6H4
4-NO2C6H4
30
75
93
87
95
87
90
90
85
85
88
87
86
90
91
89
7
10
7
95
90
96
87
91
90
87
85
90
90
87
92
92
90
308–310/this work
2
240–242/this work
3
30
283/(281–283) [39]
4
4-BrC6H4
60
7
282–285/(283–285) [39]
275/(274–276) [39]
5
4-FC6H4
60
8
6
4-ClC6H4
60
10
10
10
10
12
12
10
12
8
288–290/(288–291) [39]
268–271/(270–272) [39]
292/(292–294) [39]
7
2-CH3OC6H4
2,3-(CH3O)2C6H3
4-OH-3-NO2C6H3
4-OH-3-CH3OC6H3
3,4,5-(CH3O)3C6H2
C6H5
75
8
90
9
90
291/(290–291) [39]
10
11
12
13
14
100
120
50
246–249/(247–248) [39]
252–256/(252–254) [39]
300/(298–300) [39]
4-CH3C6H4
60
292–294/(293–294) [39]
276–280/(278–279) [39]
3-NO2C6H4
75
Table 2. The desired pure products were characterized by comparison of their
physical data (melting points, IR, and 1H NMR) with those of known compounds in
the literature. The extensive ranges of substituted and structurally various aldehydes
afforded the corresponding products in high to excellent yields using the caffeine as
123

A. Y. E. Abadi et al.
a green catalyst (Table 2). As shown in Table 2, aromatic aldehydes containing
electron-withdrawing groups increased the rate of reaction and gave higher yields
than that with electron-donating groups.
For catalyst recovery, we also investigated recycling of the caffeine using a
selected model reaction of 2-hydroxynaphthalene-1,4-dione, o-phenylenediamine,
2,4-dichlorobenzaldehyde, and malononitrile in the presence of caffeine (Table 2,
entry 1). After completion of the reaction (method B), the reaction mixture was
cooled to room temperature. Then, 5 mL of water was added to the mixture. The
caffeine was dissolved in water, and filtered for separation of the crude product. The
separated product was washed twice with water (2 9 5 mL). The resulting product
subsequently recrystallized from hot ethanol to give the pure solid. In order to
recover the catalyst, after washing the mixture with water completely, since caffeine
is soluble in water, the water including caffeine was evaporated under reduced
pressure and caffeine was recovered and reused.
As shown in Table 3, we studied the reusability of the caffeine as a green catalyst
for the same reactants. It was observed that the recovered catalyst works with the
same performance up to 2nd run, (Table 3, entries 1 and 2), while in the 3rd and 4th
runs (Table 3, entries 3 and 4) the product yield is reduced slightly, which may be
due to some weight loss of catalyst during each recovery process.
The mechanism for the formation of the products has been proposed in Scheme 2
according to the literature [39]. On the basis of this mechanism, at first,
2-hydroxynaphthalene-1,4-dione 1 tautomrizes to intermediate 7. The primary
condensation of 7 with o-phenylenediamine 2 obtain 6H-benzo[a]phenazin-5-one 8,
which in tautomerism equilibrium reasons to prepare benzo[a]phenazin-5-ol 3. On this
mechanism, caffeine is an impressive catalyst to form the olefin 9, which easily
prepares in situ from Knoevenagel condensation of aldehyde 4 with malononitrile 5.
The Michael addition of 6H-benzo[a]phenazin-5-ol 3 with benzylidenemalononitrile
9 in the presence of caffeine finally give intermediate 10, which then causes the inner
molecular ring to be formed after a tautomeric proton shift to produce 3-amino-2-
cyano-1-aryl-1H-benzo[a]pyrano[2,3-c]phenazines 6 (Scheme 2).
Table 3 Recycling and reusability of the catalyst (100 mg) for the synthesis of 3-amino-2-cyano-1-(2,4-
dichlorophenyl)-1H-benzo[a]pyrano[2,3-c]phenazine from 2-hydroxynaphthalene-1,4-dione (1 mmol), o-
phenylenediamine (1 mmol), 2,4-dichlorobenzaldehyde (1 mmol), and malononitrile (1 mmol)
Entry
Run
Method A
Method B
Time (min)
Yield (%)
Time (min)
Yield (%)
1
2
3
4
1st
30
30
30
30
93
93
90
87
7
7
7
7
95
95
92
90
2nd
3rd
4th
123

An efficient four-component domino protocol for the rapid…
Scheme 2 Proposed mechanism for the synthesis of 3-amino-2-cyano-1-aryl-1H-benzo[a]pyrano[2,3-
c]phenazines
Conclusions
In this work, we report an efficient four-component domino protocol for the rapid
and green synthesis of functionalized benzo[a]pyrano[2,3-c]phenazine derivatives
in the presence of caffeine. The synthetic procedure offers several advantages,
123

A. Y. E. Abadi et al.
including operational simplicity, clean reaction conditions, high yields, and no
pollution threat to the environment, which together make a useful and attractive
process for synthesis of these compounds. In this one-pot, two-step, four component
condensation reaction was carried out caffeine as an inexpensive, highly reactive,
non-toxic, and reusable and green solid base catalyst (environmentally friendly)
under conventional heating or microwave irradiation. Moreover, our work was
characterized by the use of microwave irradiation as a partially reproducible energy
source and avoidance of hazardous organic solvents. In all these cases, this paper
introduced a green and economically cost-effective method.
Acknowledgments We gratefully acknowledge financial support from the Research Council of the
University of Sistan and Baluchestan and Islamic Azad University of Yazd.
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