One-pot synthesis of coumarine derivatives using butylenebispyridinium hydrogen sulfate as novel ionic liquid catalyst

Article abstract of DOI:10.1007/s11164-015-2261-5

Pechmann condensation reaction of 3-hydroxyphenol and ethyl acetoacetate in the presence of 1,1′‐butylenebispyridinium hydrogen sulfate as an efficient, green, and recyclable catalyst produces 7-hydroxy-4-methylcoumarin in good yield under solvent-free conditions at room temperature. This catalyst has advantages such as the following: good to excellent yields, short reaction times, simplicity in operation, and easy workup procedure.

Full text of DOI:10.1007/s11164-015-2261-5

Res Chem Intermed
DOI 10.1007/s11164-015-2261-5
One-pot synthesis of coumarine derivatives using
butylenebispyridinium hydrogen sulfate as novel ionic
liquid catalyst
Sobhan Rezayati1 Fatemeh Sheikholeslami-Farahani2
•
•
Faramarz Rostami-Charati3 Saeid Afshari Sharif Abad1
•
Received: 6 July 2015 / Accepted: 3 September 2015
Ó Springer Science+Business Media Dordrecht 2015
Abstract Pechmann condensation reaction of 3-hydroxyphenol and ethyl ace-
toacetate in the presence of 1,10-butylenebispyridinium hydrogen sulfate as an
efficient, green, and recyclable catalyst produces 7-hydroxy-4-methylcoumarin in
good yield under solvent-free conditions at room temperature. This catalyst has
advantages such as the following: good to excellent yields, short reaction times,
simplicity in operation, and easy workup procedure.
Keywords (Bbpy)(HSO4)2 Á Ionic liquid Á Solvent-free conditions Á Pechmann
condensation
Introduction
Coumarins an important class of compounds whose synthesis has been the focus of
attention from many organic and medicinal chemists because of the broad spectrum
of their biological and pharmaceutical properties. These properties include
anticancer [1], antibacterial [2], inhibitory of HIV-1 protease [3], and inhibition
of platelet aggregation [4]. Coumarins are also used as intermediates for the
synthesis of chromenes, coumarones, fluorocoumarins, and 2-acylresorcinols [5].
Several synthetic procedures have been used for the synthesis of coumarins, such as
Knoevenagel condensation [6–8], Pechmann condensation [9], Claisen [10],
&
Fatemeh Sheikholeslami-Farahani
sheikholeslamy@yahoo.com
1
2
3
Department of Chemistry, Qaemshahr Branch, Islamic Azad University,
P.O. Box 163, Qaemshahr, Iran
Department of Chemistry, Firookooh Branch, Islamic Azad University, Firoozkooh, Tehran,
Iran
Department of Chemistry, Faculty of Science, Gonbad Kavous University,
P.O. Box 163, Gonbad, Iran
123

S. Rezayati et al.
O
O
OH
O
O
(Bbpy)(HSO4)2
Solvent-Free, r.t.
R
R
H3C
OEt
CH3
1
2
3 (a-m)
Scheme 1 Synthesis of coumarin derivatives by Pechmann condensation
Reformatsky [11], and Wittig reaction [12]. However, Pechmann reaction is the
most common and simplest procedure for the synthesis of various coumarin-based
phenols and b-keto esters or unsaturated carboxylic acids under acid catalysis. In
recent years, different acid catalysts have been used in Pechmann condensation [13–
18]. Most of these methods have severe drawbacks including the use of a large
amount of catalysts, for example, sulfuric acid 10–12 equivalents [13], trifluo-
roacetic acid 3–4 equivalents [14], and phosphorous pentoxide is required in a
fivefold excess [15]. Thus, often high temperatures [16, 17], hard reaction
conditions [18], low yield of products being hard to purify, poor selectivity, use
of toxic or highly expensive reagents [19, 20], and also the disposal of acidic waste
leads to environmental pollution. Various ionic liquids are reported for the synthesis
of coumarin [21–23]. In addition, ionic liquids are readily recycled and tunable to
specific chemical tasks. (Bbpy)(HSO4)2 is a low-cost, readily available acidic
material. Recently, (Bbpy)(HSO4)2 has been used as a versatile mediator or an
efficient Brønsted acidic ionic liquid catalyst for the one-pot multi-component
synthesis of unsymmetrical polyhydroquinoline derivatives, which were reported
for the first time by Ghaffari Khaligh [24]. As part of our continuing interest in the
development of new synthetic methodologies [25–29], we wish to report an efficient
and green procedure for the synthesis of coumarin derivatives by Pechmann
condensation in the presence of (Bbpy)(HSO4)2 as a catalyst under solvent-free
conditions at room temperature (Scheme 1). This procedure is better and more
simple than the other procedures to synthesize coumarin derivatives in terms of the
amount of the loading catalyst, reaction conditions, product yields, and the required
temperature.
Experimental
General
Chemicals were either prepared in our laboratories or they were purchased from
Aldrich or Fluka chemical companies. The products were isolated and identified by
comparing their physical, melting point, and spectral data with those in the
literature. NMR spectra were recorded at room temperature on a Bruker AM 250
1
spectrometer at 250 MHz for H and 62.5 MHz for 13C, respectively, using CDCl3
as solvent. Chemical shifts are expressed in d values (ppm) relative to TMS as
internal standard for 1H and relative to TMS (0.00 ppm) or to CDCl3 (77.05 ppm)
123

One-pot synthesis of coumarine derivatives using…
for 13C NMR spectra. Melting points were determined on an electrical melting point
apparatus in an open capillary and uncorrected. The progress of the reaction was
followed with thin-layer chromatography (TLC) using silica gel SILG/UV 254 and
365 plates.
Synthesis of 1,10-butylenebispyridinium hydrogen sulfate (Bbpy)(HSO4)2
In this study, pyridine (0.95 g, 12.01 mmol), 1,4-dichlorobutane (0.80 g,
6.30 mmol), and dry acetonitrile (10 mL) were added into a two-neck 100-mL
round bottomed flask equipped with a reflux condenser and magnetic stirrer. The
mixture was refluxed for 48 h. After the reaction, the solvent was removed under
vacuum, and the residue was washed with dichloromethane and dried at 60 °C under
vacuum to give 1,1-butylenebispyridinium dichloride (Bbpy)Cl2 as a white solid
(1.68 g, 98.2 %). To a stirred solution of (Bbpy)Cl2 (1.40 g, 4.91 mmol) in 25 mL
dry CH2Cl2 at 0 °C was added dropwise 98 % H2SO4 (0.53 mL, 9.82 mmol) over
10 min. The resulting solution was refluxed for 48 h, and then the solution was
washed with a mixture of ethanol and water (50 %, 2 9 5 mL). The solvent was
distilled off under reduced pressure to give (Bbpy)(HSO4)2 as a darkish viscous
liquid (1.96 g, 98 %) [24].
General procedure for the coumarin derivatives 3a–3m
In a round-bottom flask (25 mL), (Bbpy)(HSO4)2 (10 mg, 2.4 mol %) was added to
the mixture of 3-hydroxy phenol (5.0 mmol) and ethyl acetoacetate (5.0 mmol) and
the reaction mixture stirred at ambient temperature for the appropriate time
(Table 2). The progress of reaction was monitored by TLC (eluent, n-hexane:ethyl
acetate, 4:1). After the completion of the reaction, water (10.0 mL) was added to the
reaction mixture, and the catalyst was recovered by filtration. Evaporation of the
solvent from the filtrate and recrystallization of the solid residue from hot ethanol
afforded the pure products in good to excellent yields. All compounds were
1
identified by comparison of melting point, H NMR, and 13C NMR with those
reported. Spectroscopic data for selected examples listed below.
7-Amino-4-methyl-2H-chromen-2-one (Table 2, Entry 4)
1H-NMR (250 MHz; CDCl3): d 7.35–7.39 (d, J = 8.5 Hz, 1H), 6.52–6.56 (dd,
J = 6 Hz, J = 2.25 Hz, 1H), 6.37–6.38 (d, J = 2.25 Hz, 1H), 6.06 (broad s, 2H),
5.873-5.877 (s, 1H), 2.272-2.276 (s, 3H); 13C-NMR (62.9 MHz, CDCl3): d 161.2,
155.9, 154.2, 153.5, 126.6, 111.6, 109.3, 107.9, 98.9, 18.4.
7,8-Dihydroxy-4-methyl-2H-chromen-2-one (Table 2, Entry 5)
1H-NMR (250 MHz; CDCl3): d 9.12–10.15 (broad s, 2H), 7.03–7.07 (d,
J = 8.5 Hz, 1H), 6.69–6.80 (d, J = 8.5 Hz, 1H), 6.08 (s, 1H), 2.31 (s, 3H) ppm.
13C-NMR (62.9 MHz, CDCl3): d 160.6, 154.3, 149.8, 143.8, 132.6, 115.9, 113.2,
112.6, 110.6, 18.7.
123

S. Rezayati et al.
4-Methyl-2H-benzo[h]chromen-2-one (Table 2, Entry 10)
1H-NMR (250 MHz; CDCl3): d 8.32–8.35 (m, 1H), 8.00-8.03 (m, 1H), 7.65–7.86
(m, 4H), 6.480 (s, 1H), 2.506 (s, 3H); 13C-NMR (62.9 MHz, CDCl3): d 160.1,
154.6, 134.8, 129.1, 128.4, 127.8, 124.4, 122.6, 122.0, 121.7, 115.5, 114.3, 19.1.
6-Hydroxy-4-methyl-2H-chromen-2-one (Table 2, Entry 13)
1H-NMR (250 MHz; CDCl3): d 9.71 (s, 1H), 7.18–7.22 (broad s, 1H), 7.00 (broad s,
2H), 6.332 (s, 1H), 2.342 (s, 3H), 13C-NMR (62.9 MHz, CDCl3): d 160.5, 154.2,
153.2, 146.7, 120.6, 120.2, 117.8, 114.9, 110.0, 18.5.
Results and discussion
1,10-butylenebispyridinium hydrogen sulfate (Bbpy)(HSO4)2 was prepared readily
in the two-step process as detailed in the literature (Scheme 2). In first step, two
equivalents of pyridinium was alkylated with 1,4-dichlorobutane in acetonitrile
under reflux conditions for 24 h. In the second step, by adding H2SO4 in dry CH2Cl2
under reflux conditions for 48 h the resulting halide 1,10-butylenebispyridinium
dichloride (Bbpy)Cl2 converted to 1,10-butylenebispyridinium hydrogen sulfate
(Bbpy)(HSO4)2 and was isolated as a viscous liquid.
An informative technique for an investigation of catalyst formation is FT-IR
spectroscopy. The FT-IR spectrum of the catalyst (Fig. 1) was recorded using the
KBr disc technique. The O=S=O asymmetric and symmetric stretching modes of the
sulfonic acid functional groups were found in the ranges 1020–1060 cm-1
,
respectively, and that of the S–O stretching mode at 1227 cm-1. Also, one
absorption was seen at 1637 for C=N cm-1 and 1400 cm-1 for the C=C group. The
spectrum also showed a broad OH stretching absorption around 3144 and
3465 cm-1
.
For understanding the efficiency of 1,1-butylenebispyridinium hydrogen sulfate
to the Pechmann condensation, the reaction of ethyl acetoacetate 1 (5 mmol) with
resorcinol 2 (5 mmol) under solvent-free conditions at room temperature was
selected as the model reaction (Scheme 1). Firstly, when the reaction was carried
out in the absence of 1,1-butylenebispyridinium hydrogen sulfate, the reaction was
slow and 7-hydroxy-4-methylcoumarin weren’t formed after 24 h (Table 1, Entry
1). The results listed in Table 1 show that when the reaction was performed in the
presence of 3 mg of 1,1-butylenebispyridinium hydrogen sulfate, coumarin 3a was
HSO4
Cl
N
H2SO4 (98%), dry CH2Cl2
0 oC, Reflux, 48 h
N
Dry acetonitrile
Reflux, 48 h
N
N
Cl
Cl
HSO4
98%
Cl
N
(Bbpy)(HSO4)2
(Bbpy)Cl2
98.2%
Scheme 2 Synthesis of 1,10-butylenebispyridinium hydrogen sulfate (Bbpy)(HSO4)2
123

One-pot synthesis of coumarine derivatives using…
Fig. 1 The FT-IR spectrum of 1,1-butylenebispyridinium hydrogen sulfate (KBr disc)
Table 1 Optimization of the amount of (Bbpy)(HSO4)2 catalyst under solvent-free conditions for the
synthesis of 3a
Entry
Loading catalyst (mg)
Time (min)
Yield (%)b
1
2
3
4
5
6
7
8
9
None
1
24 ha
80
10c
65
76
85
95
79
71
66
53
3
50
5
35
10
15
20
25
50
25
30
30
30
30
Model reaction resorcinol (5.0 mmol) and ethyl acetoacetate (5.0 mmol) in the presence of
(Bbpy)(HSO4) under solvent-free conditions and at ambient temperature
a
In hours
b
Yield of isolated products
c
Not completed
achieved in good yield (Table 1, Entry 3). The best result was obtained when we
used 10 mg of 1,1-butylenebispyridinium hydrogen sulfate, which leads to the
formation of the 7-hydroxy-4-methylcoumarin in excellent yield and with short
reaction times (95 %, 25 min) (Table 1, Entry 5). When the reaction was carried out
in 15 mg of 1,1-butylenebispyridinium hydrogen sulfate, there was less yield of
product (Table 1, Entry 6). Increasing the amount of catalyst until 15 mg had no
positive effect on the product yield (Table 1, Entries 7–9). After optimization of the
reaction conditions, other phenols were examined with ethyl acetoacetate in the
presence of 10 mg of 1,1-butylenebispyridinium hydrogen sulfate under solvent-
free conditions and at room temperature. The results are presented in Table 2.
123

S. Rezayati et al.
Table 2 (Bbpy)(HSO4)2-catalyzed synthesis of coumarins via Pechmann reaction
O
O
OH
O
O
(Bbpy)(HSO4)2
Solvent-Free, r.t.
R
R
H3C
OEt
CH3
M.p. (°C)
Entry
1
Substrate
Product
Time
(min)
Yield
(%)a
Found
Reported [lit.]
184–186 [30]
25
95
183–184
HO
O
O
HO
OH
Me
O
3a
3b
2
3
35
35
85
89
132–133
158–160
131–133 [30]
160–162 [30]
Me
O
Me
OH
OH
Me
O
MeO
MeO
O
Me
3c
4
5
40
25
90
95
223–225
239–240
222–224 [30]
241–243 [30]
H2N
OH
OH
H2N
O
O
Me
3d
OH
OH
HO
HO
HO
O
O
O
HO
Me
O
3e
6
7
20
30
97
94
280–2822
260–262
83–285 [30]
258–260 [30]
OH
OH Me
HO
HO
OH
OH
3f
O
O
Me
Me Me
3g
123

One-pot synthesis of coumarine derivatives using…
Table 2 continued
Entry
Substrate
Product
Time
(min)
Yield
(%)a
M.p. (°C)
Found
Reported [lit.]
137–139 [30]
8
20
93
135–136
OH
OH
O
O
O
OH
Me
3h
O
9
120
55
65
89
82–83
80–82 [30]
OH
Me
3i
10
154–155
154–156 [30]
OH
OH
O
O
Me
3j
11
NO2
35
91
185–187
183–185 [31]
NO2
O
O
Me
3k
12
13
25
30
93
95
152–153
241–243
151–154 [31]
242–244 [32]
HO
O
O
O
NO2
O2N
HO
Me
O
3l
HO
OH
3m
Model reaction resorcinol (5.0 mmol) and ethyl acetoacetate (5.0 mmol) in the presence of
(Bbpy)(HSO4) (10 mg) under solvent-free conditions and at ambient temperature
a
Yield of isolated products
The results listed in Table 2 show that the rate of reactions were increased in the
presence resorciniol (Table 2, Entry 1), pyrogallol (Table 2, Entry 5), phloroglu-
cinol (Table 2, Entry 6), orcinol (Table 2, Entry 7), 2,6-dihydroxy toluene (Table 2,
Entry 8), 4-nitro phenol (Table 2, Entry 12), and hydroquinone (Table 2, Entry 13)
and produce coumarin derivatives in excellent yields. Also, 3-aminophenol
(Table 2, Entry 4) reacted to provide the amino coumarin derivatives in good yield
123

S. Rezayati et al.
with slightly longer reaction times. 1-Naphtol (Table 2, Entry 10) reacted with
longer reaction time and low yield due to having another phenyl group. Similarly,
phenol (Table 2, Entry 9) reacted with longer reaction time and very low yield, but
on the other hand, formation of 4-methylcoumarin in acceptable yield from the
reaction of unsubstituted phenol. The products obtained were purified by
recrystallisation in hot ethanol, and the structures of the products 3a–3m were
1
1
deduced from the H NMR and 13C NMR spectra. For example, the H NMR
spectrum of 3e exhibited one singlet for OH group at 6.08 ppm, one singlet for CH3
protons at 2.31 ppm, two doublets at 7.03–7.07 (d, 3J = 8.5 Hz), and 6.76–6.80 (d,
3J = 8.5 Hz) for C–H proton. The 13C NMR spectrum of 3e displayed ten distinct
resonances in agreement with the proposed structure of product. The reaction
pathway proposed for the Pechmann condensation of resorcinol with ethyl
acetoacetate in the presence of (Bbpy)(HSO4)2 as the catalyst has been described
(Scheme 3). It is suggested that ethyl acetoacetate in the presence of catalyst
produce intermediate 4. Resorcinol react with 4 and generate intermediate A.
Interamolecular cyclization and elimination EtOH led to formation intermediate
B. Finally, the intermediate B undergoes elimination of water to give target product
3a.
In order to show the merit of (Bbpy)(HSO4)2 with recently reported protocols,
some homogeneous and heterogeneous catalysts in the Pechmann condensation with
resorciniol (1) and ethyl acetoacetate (2) are presented in Table 3. The results
H
H
H
H
O
O
O
O
O
O
O
O
Me
(Bbpy)(HSO4)2
EtO
Me
EtO
Me
OEt
H
HO
HO
A
-H+
H
H
O
O
Me
O
Me
HO
O
O
OEt
-H2O
-EtOH
HO
O
O
HO
O
H
Me
B
7-Hydroxy-4-methyl coumarin
HSO4
H
N
N
HSO4
Scheme 3 Proposed mechanism for the Pechmann condensation of resorcinol with ethyl acetoacetate in
the presence of (Bbpy)(HSO4)2 catalyst
123

One-pot synthesis of coumarine derivatives using…
Table 3 Comparison of the catalytic efficiency of (Bbpy)(HSO4)2 against other catalysts used for the
synthesis of 7-hydroxy-4-methylcoumarin
Entry
Catalyst/solvent/temperature
Time (min)
Yield (%)
References
1
CMK-5-SO3H/solvent-free/130 °C
Iodine/toluene/90 °C
ZrCl4/ambient temperature
20
18c
5
95
89
92
95
94
97
91
85
87
96
88
87
94
95
[16]
[21]
[22]
[23]
[30]
[33]
[34]
[35]
[36]
[37]
[38]
[38]
[39]
–
2
3
4
[bmim]ClÁ2AlCla3/solvent-free/30 °C
10
50
30
24c
45
0.7c
4c
5
PS/GaClb3/EtOH/reflux
6
Mg–Al–CO3/solvent-free/70 °C
Sulfated zirconia/solvent-free/80 °C
TiO2–Pr–SO3H/solvent-free/90 °C
H6P2W18O62Á24H2O/solvent-free/130 °C
Mont-K10/solvent-free/150 °C
Mont-KSF/solvent-free/150 °C
In(OTf)3/solvent-free/80 °C
7
8
9
10
11
12
13
15d
a
5c
32
30
25
H3PW12O40/solvent-free/90 °C
(Bbpy)(HSO4)2/solvent-free/room temperature
1-Butyl-3-methylimidazolium chloroaluminate
b
c
d
Polystyrene-supported GaCl3
In hour
Our work
clearly show that some catalysts such CMK-5-SO3H (Table 3, Entry 1), iodine
(Table 3, Entry 2), chloroaluminate (Table 3, Entry 9), Mont-K10 (Table 3, Entry
10), and Mont-KSF (Table 3, Entry 11) requires high temperatures and longer
reaction time for completion of the reaction. On the other hand, polystyrene-
supported GaCl3 and PVPP-BF3 (Table 3, Entry 5) used in reflux conditions, which
are hard reaction conditions. Also, some used from toxic solvents such as toluene,
which had dangerous reaction conditions and much longer reaction times (Table 3,
Entry 2). As can be seen, our procedure was simpler and more efficient, without the
need for temperature and toxic solvents, and used a lower amount of the catalyst,
which shows (Bbpy)(HSO4)2 is a powerful catalyst for the synthesis coumarin
derivatives, thus without doubt, our procedure is a clean and environmentally
friendly reaction.
The recoverability and reusability of (Bbpy)(HSO4)2 was checked for the
synthesis of coumarin derivatives. It was found that the (Bbpy)(HSO4)2 could be
reused several times without any appreciable loss of activity (Table 4). After the
completion of the reaction of ethyl acetoacetate (5 mmol), resorcinol (5 mmol), and
(Bbpy)(HSO4)2 (10 mg) as a model reaction, the catalyst was filtered, washed with
chloroform (10 mL). As depicted in Table 4, the recoverability and reusability of
catalyst was also checked for the synthesis of other coumarin derivatives. This
process was repeated for five cycles, and each run afforded the desired product in
good to excellent yield. The decrease in activity can be mainly attributed to
unavoidable loss of the catalyst during the process of collection and washing.
123

S. Rezayati et al.
Table 4 The reusability of (Bbpy)(HSO4)2 for the preparation of coumarin derivatives
Product
Yield (%)
(cycle 1)
Yield (%)
(cycle 2)
Yield (%)
(cycle 3)
Yield (%)
(cycle 4)
Yield (%)
(cycle 5)
3a
3f
95
97
94
94
95
93
93
95
92
93
94
92
92
92
92
3g
Conclusion
In summary, an efficient and environmentally friendly procedure for the synthesis of
coumarin derivatives using (Bbpy)(HSO4)2-catalyzed through Pechmann conden-
sation reaction between ethyl acetoacetate with various phenol under solvent-free
conditions and at ambient temperature was described. Mild reaction conditions,
short reaction times, good to excellent yield independent of temperature, simple
experimental and product isolation procedures are the significant advantages of the
present method.
Acknowledgments We gratefully acknowledge financial and spiritual support from Islamic Azad
University of Qaemshahr and Gonbad Kavous University.
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