Microwave assisted convenient one-pot synthesis of coumarin derivatives via Pechmann condensation catalyzed by FeF3 under solvent-free conditions and antimicrobial activities of the products

Article abstract of DOI:10.3390/molecules190913093

A rapid and efficient solvent-free one-pot synthesis of coumarin derivatives by Pechmann condensation reactions of phenols with ethyl acetoacetate using FeF₃ as a catalyst under microwave irradiation is described. This one-pot synthesis on a solid inorganic support provides the products in good yields. The newly synthesized compounds were systematically characterized by IR, ¹H-NMR, ¹³C-NMR, MS and elemental CHN analyses. The proposed solvent-free microwave irradiation method using the environmentally friendly catalyst FeF₃ offers the unique advantages of high yields, shorter reaction times, easy and quick isolation of the products, excellent chemoselectivity, and a one-pot, green synthesis. The products were screened for antimicrobial activity, and the results showed that the compounds reacted against all the tested bacteria.

Full text of DOI:10.3390/molecules190913093

Molecules 2014, 19, 13093-13103; doi:10.3390/molecules190913093
OPEN ACCESS
molecules
ISSN 1420-3049
www.mdpi.com/journal/molecules
Article
Microwave Assisted Convenient One-Pot Synthesis of Coumarin
Derivatives via Pechmann Condensation Catalyzed by FeF3
under Solvent-Free Conditions and Antimicrobial Activities of
the Products
†,
†
Vahid Vahabi * and Farhad Hatamjafari
Department of Chemistry, Faculty of Science, Islamic Azad University-Tonekabon Branch,
Tonekabon 46841-61167, Iran; E-Mail: f_hatamjafari@tonekaboniau.ac.ir
†
These authors contributed equally to this work.
*
Author to whom correspondence should be addressed; E-Mail: vahidvahabi20@gmail.com;
Tel.: +98-192-427-1109; Fax: +98-192-427-4409.
Received: 30 June 2014; in revised form: 4 August 2014 / Accepted: 11 August 2014 /
Published: 26 August 2014
Abstract: A rapid and efficient solvent-free one-pot synthesis of coumarin derivatives by
3
Pechmann condensation reactions of phenols with ethyl acetoacetate using FeF as a
catalyst under microwave irradiation is described. This one-pot synthesis on a solid
inorganic support provides the products in good yields. The newly synthesized compounds
1
13
were systematically characterized by IR, H-NMR, C-NMR, MS and elemental CHN
analyses. The proposed solvent-free microwave irradiation method using the environmentally
3
friendly catalyst FeF offers the unique advantages of high yields, shorter reaction times,
easy and quick isolation of the products, excellent chemoselectivity, and a one-pot, green
synthesis. The products were screened for antimicrobial activity, and the results showed
that the compounds reacted against all the tested bacteria.
Keywords: coumarin; solvent-free; FeF3; one-pot; microwave irradiation;
antimicrobial activities

Molecules 2014, 19
. Introduction
Coumarin and its derivatives are biologically and pharmacologically active compounds with a wide
13094
1
range of properties as antitumor, antimicrobial, anti-HIV, anticoagulant, anti-inflammatory and
antioxidant agents [1,2]. In particular, the antitumor activity of coumarin compounds has received
considerable attention among researchers. Coumarins belong to the flavonoid class of compounds that
are mainly isolated from natural plants. In addition, some coumarins are also found in microorganisms,
for example, in antibiotics such as novobiocin, coumermycin A1, and chlorobiocin [3,4]. Coumarin
derivatives are typically synthesized by chemical modification of the coumarin ring. Owing to their
diverse pharmacological properties and natural sources of origin, coumarins play an important role in
the synthesis of natural products [5–7]. Furthermore, coumarins find widespread applications in a
broad range of fields, including foods, cosmetics, as dispersive fluorescent laser dyes, as
light-activated compounds in the field of medicine, and as anticoagulants in the production of
pesticides [8]. Recently, several improved synthetic methodologies have been developed that use a
variety of Lewis acid catalysts [9–12], phase transfer catalysts [13–17], microwave reactions [18], and
molecular iodine [19]. Some of these methods are expensive, environmentally unfriendly, produce low
yields, are incompatible with other functional groups, and involve labor-intensive product isolation
procedures. Thus far, several methods, including Perkin [20], Knoevenagel [21], Reformatsky [22],
Wittig [23], and Pechmann [24] reactions, have been adopted for the synthesis of coumarins.
Therefore, a simple, efficient, and green chemistry for one-pot coumarins synthesis under mild
conditions is required. The method presented herein involves the condensation of phenols with
β-ketoesters, often in the presence of acid, which acts as a catalyst for the synthesis of coumarins. The
superiority of use of FeF to the current process is demonstrated in comparison with other Lewis acids,
3
Fe-salts, fluoride sources and insights into the origin of the efficiency are discussed [25,26].
Previously, we have synthesized a number of heterocyclic compounds [27–36]. In this study, we
have used of analyzed the Pechmann reaction to develop a new and suitable methodology for the
synthesis of coumarins. The experiments were started with the study of one-pot, two-component
3
Pechmann condensation using FeF as a catalyst under solvent-free microwave irradiation (Scheme 1).
Scheme 1. FeF
3
catalyzed Pechmann reaction.
OH
O
O
O
O
FeF Solvent-Free
3
,
+
MW, 450 W, 110 °C
OR
R'
R'
2
. Results and Discussion
Coumarins occupy an important place in the realm of natural products and synthetic organic
chemistry. Coumarins are simple heterocyclic compounds that can be obtained from natural sources,
especially green plants. They are used in food additives, perfumes, cigarettes, cosmetics,
pharmaceuticals, light-activated compounds, and fluorescent laser dyes.

Molecules 2014, 19
13095
a
Table 1. FeF catalyzed synthesis of coumarin derivatives .
3
Entry
Phenol
Product
Time (min) Yield (%)
MP °C, (Lit) [ref.]
OH
O
O
1
8
9
97
98
80–82, (81) [37]
OH
OH
O
O
2
3
132–135, (131–133) [9]
172–174, (171–172) [9]
O
O
9
93
HO
HO
O
O
HO
OH
4
5
7
7
95
94
185–188, (184–185) [9]
258–260, (257–260) [38]
HO
HO
OH
OH
O
O
O
HO
O
6
7
8
8
7
6
89
90
92
135–138, (137–138) [37]
235–236, (234–237) [37]
281–284, (280–281) [9]
OH
OH
HO
HO
O
O
O
O
HO
HO
OH
OH
OH
OH
OH
O
O
9
6
93
165–170, (169–170) [9]
O
O
O
O
OH
1
0
1
7
8
87
85
176–180, (180–182) [9]
153–156, (154–155) [9]
OH
O
O
1
1
OH
OH
O
O
O
O
2
3
9
8
61
71
165–169
160–162
1
1
OH
O
O
4
9
66
168–170
a
3
Reaction conditions: phenols (1 mmol), ethyl acetoacetate(1 mmol), FeF (0.05 g), Isolated yield.
In this research, we have synthesized some coumarins derivatives using phenols and ethyl
acetoacetate in the presence of FeF as a catalyst to create the corresponding products, as illustrated in
3
the model reaction (Scheme 1). The synthesis of compound 4 was selected as the model to optimize
the reaction conditions. The corresponding results are summarized in Table 1. As can be seen from the
3
results presented in this table, FeF acts as an effective catalyst, significantly increasing the reaction
rate; moreover, it can be easily separated (Table 1). All the reactions were monitored by using thin
layer chromatography (TLC) and carried forward to maximum atom utilization. In addition, all the

Molecules 2014, 19
13096
products were characterized by using melting points, infrared spectroscopy (IR), proton nuclear magnetic
1
13
resonance spectroscopy ( H-NMR), carbon-13 nuclear magnetic resonance spectroscopy ( C-NMR),
mass spectroscopy and carbon, hydrogen, and nitrogen analysis (CHN). The results obtained from
these systematic analysis were found to be in good agreement to those reported in the literature.
We have also carried out the model reaction under microwaves using different powers, and it was
found that if the reactions are carried out without microwave irradiation they takes more time (60 min)
and give negligible yields (26%). As the power increases (100, 250, 300, 450, 600 W), there is increase
in yield with a corresponding decrease in reaction time up to 450 W, but no significant change is
observed at 600 W. Hence, we selected 450 W at 110 °C and 1 atm pressure for all the subsequent
reactions. The different reaction conditions obtained by varying the amount of catalyst and the
corresponding results are summarized in Table 2. It could be observed that the product yield is strongly
affected by the amount of catalyst used in the reaction. Best results were obtained in under solvent-free
microwave irradiation (Entry 4) using 0.05 g of catalyst.
Table 2. FeF catalyzed synthesis of 7-hydroxy-4-methyl-chromen-2-one (4) in various
3
a
amount of the catalyst under solvent-free microwave irradiation .
NO.
1
2
3
4
5
6
7
8
Catalyst (g)
-
Yield (%)
15
69
86
95
91
89
87
85
0.02
0.04
0.05
0.06
0.07
0.08
0.10
a
Reaction conditions: resorsinol (1 mmol), ethyl acetoacetate (1 mmol), and catalyst at 7 min; Isolated yield.
To compare the efficiency of the solvent-free versus solution conditions, the reaction was examined
in several solvents and solvent-free under microwave irradiation. Thus, a mixture of resorsinol
(
3
1 mmol), ethyl acetoacetate (1 mmol), and FeF (0.05 g) was heated under microwave irradiation for
7
min in different solvents. The results are listed in Table 3. As it is clear from the results, lower yields
and longer reaction times were observed under solution conditions. Therefore, the solvent-free methid
offers the as a best and more efficient conditions.
Table 3. FeF catalyzed synthesis of 7-hydroxy-4-methyl-chromen-2-one (4) under various
3
solvent and solvent-free conditions.
NO.
1
2
3
4
5
6
7
8
Solvent
solvent-free
DMF
Yield (%)
95
57
63
49
64
81
80
74
acetonitrile
dichloromethane
water
ethanol
methanol
dioxane

Molecules 2014, 19
13097
Comparison of reaction conditions and product yield between previously reported methods and the
reaction of resorcinol with ethyl acetoacetate (Table 1, Entry 4) in the presence of different catalysts is
shown in Table 4. The catalyst was easily recovered by simple filtration after dilution of the reaction
mixture with ethyl acetate and was reused after being vacuum dried. FeF was reused for four runs without
3
significant loss of activity (Run 1: 95%; Run 2: 92%; Run 3: 89%; Run 4: 87%; Run 5: 82%).
Table 4. Reaction of resorcinol with ethyl acetoacetate (Table 1, Entry 4) in the presence
of different catalysts.
Entry
Catalyst/mol%
Ce(OTf)4/1
Conditions
Reaction Time (min)
Yield (%)
Reference
[39]
1
2
3
4
H
2
O/Room Temperature
Toluene/110 °C
15
180
50
92
90
65
95
30
67
95
PFPAT/10
[39]
MFRH/0.05 g
Oxalic acid/10
Nanoreactors/7
Solvent free/80 °C
Solvent free/80 °C
[39]
30
[39]
Solvent free/130 °C
60
[39]
5
5
FeF /0.05 g
Heating/Ethanol, reflux
Microwaves
120
7
This Research
This Research
3
3
FeF /0.05 g
All the title compounds 1–14 were screened for their antimicrobial activity. They were first
screened for anti-bacterial activity against the growth of Staphylococcus aureus (Gram + ve) and
Escherichia coli (Gram − ve) at different concentrations (100, 50, 25 ppm) by the disk diffusion
method. All the compounds show good activity against both bacteria when compared to the reference
compound penicillin. Then next they were subjected to antifungal activity evaluation against the
growth of Aspergillus niger and Helminthosporium oryzae at various concentrations (100, 50, 25 ppm)
with griseofulvin as the standard reference compound. The inhibition zone results of title compounds
were presented in Table 5. The majority of the compounds showed good antifungal activity against
both fungi, especially compounds 3, 7, 10 and 12.
Table 5. Antimicrobial activity of the compounds 1–14 (µg/mL).
Zone of Inhibition (%)
Antibacterial Activity
Antifungal Activity
Compound
Escherichia coli Staphylococcus aureus Aspergillus niger Helminthosporium oryzae
1
00 50 25
100
22
21
23
21
21
22
23
22
21
23
20
23
21
22
20
50
10
10
12
10
12
12
12
11
12
10
10
12
10
10
12
25
6
5
6
5
6
7
7
5
5
6
6
8
6
5
8
100
20
18
19
21
18
19
21
20
20
21
20
20
19
20
20
50
10
12
13
11
11
9
14
12
12
13
10
12
11
11
10
25
7
6
8
7
6
4
8
4
6
6
5
7
5
4
5
100
13
19
13
19
13
18
20
14
19
20
19
20
16
15
20
50
8
12
7
10
7
10
15
9
10
11
11
10
8
25
5
7
4
7
4
5
8
5
7
6
6
5
6
5
5
1
2
3
4
5
6
7
8
9
21
10
11
12
12
11
10
14
10
11
12
10
13
10
11
12
5
6
7
7
6
6
8
5
7
8
5
7
5
5
8
22
23
20
22
22
24
21
21
23
21
23
22
22
20
10
11
12
13
14
9
10
Penicillin Griseofulvin

Molecules 2014, 19
13098
3. Experimental Section
3.1. General Information
Melting points were measured on an Electrothermal 9100 apparatus. All reactions were carried out
TM
in a CEM MARS 5 microwave oven. The TLC was performed with silica gel SILG/UV 254 plates.
1
13
IR spectra were measured using a Shimadzu IR-470 spectrophotometer. H- and C-NMR spectra
were determined on a Bruker 400 DRX AVANCE instrument at 400 and 100 MHz, respectively. The
elemental analyses (C, H) were conducted using Carlo ERBA Model EA 1108 and Perkin-Elmer 240c
analyzers. Mass spectra were recorded on a Jeol JMSD-400 spectrometer.
3
.2. Typical Procedure Adopted for the Synthesis of 7-Hydroxy-4-Methyl-Chromen-2-One (4)
A mixture of resorsinol (1 mmol), ethyl acetoacetate (1 mmol), and FeF (0.05 g) was ground in an
3
open Pyrex beaker and the homogenized mixture was heated by microwave irradiation for about
min, as indicated in Table 1. The progress of the reaction was monitored by using TLC (ethyl
7
acetate/n-hexane: 1/2). After complete conversion as indicated by TLC, the mixture was extracted with
petroleum ether (3 × 30 mL) and washed with water (3 × 30 mL). The crude products were purified by
recrystallization from ethanol (95%) to afford pure products. Data for new compounds are listed below:
−
1
4
,5,6,7-Tetramethyl-2H-chromen-2-one (12): Yellow solid; m.p.: 165–169 °C; IR (KBr) νmax (cm ): 1674
1
(ester C=O stretch), 1602 (C−C=C stretch); H-NMR (DMSO-d
6
1
) δ: 2.12 (s, 3H, CH
3
), 2.20 (s, 3H, CH
) δ: 14.4, 17.6, 21.8,
3.7, 114.5, 117.0, 121.7, 125.6, 131.8, 133.7, 152.1, 158.8. MS (m/z): 202 (M+); Anal. Calcd for
: C, 77.30; H, 7.03%. %. Found: C, 77.15; H, 6.86%.
3
),
3
3 3 6
2.31 (s, 3H, CH ), 2.42 (s, 3H, CH ), 6.25 (m, 1H), 7.24 (s, 1H); C-NMR (DMSO-d
2
13 14 2
C H O
−
1
6
-Ethyl-4-methyl-2H-chromen-2-one (13): Yellow solid. m.p.: 160–162 °C. IR (KBr) νmax (cm ): 1666
1
(ester C=O stretch), 1589 (C−C=C stretch). H-NMR (DMSO-d
6
) δ: 1.85 (t, J = 7.2, 3H, CH
3
), 2.38 (s,
3
3 2
H, CH ), 3.63 (q, J = 7.2, 2H, CH ), 5.91 (m, 1H), 7.11 (d, J = 8.5, 1H), 7.34 (dd, J = 8.5, 2.2, 1H), 7.41
13
(s (br), 1H); C-NMR (DMSO-d ) δ: 16.8, 18.8, 22.4, 115.4, 118.6, 123.3, 124.8, 130.9, 135.1, 155.3,
6
12 2
161.2. MS (m/z): 188 (M+). Anal. Calcd for C12H O : C, 76.57; H, 6.43%. Found: C, 77.25; H, 6.38%.
−
1
6
1
2
2
1
-Isopropyl-4-methyl-2H-chromen-2-one (14): Yellow solid; m.p.: 168–170 °C. IR (KBr) νmax (cm ):
1
658 (ester C=O stretch), 1585 (C−C=C stretch). H-NMR (DMSO-d
6
) δ: 1.65 (d, J = 6.5, 1H, CH),
.44 (s, 3H, CH
.3, 1H), 7.45 (s (br), 1H); C-NMR (DMSO-d
33.4, 137.3, 157.4, 163.5. MS (m/z): 202 (M+). Anal. Calcd for C13
3
), 2.95 (q, J = 6.5, 6H, 2CH
3
), 5.89 (m, 1H), 7.15 (d, J = 8.3, 1H), 7.30 (dd, J = 8.3,
) δ: 14.8, 15.6, 18.5, 24.9, 116.7, 119.2, 122.7, 126.9,
: C, 77.20; H, 6.98%.
1
3
6
14 2
H O
Found: C, 76.55; H, 6.68%.
.3. Antimicrobial Activity
The compounds 1–14 were screened by the disk diffusion method [40,41], for their antimicrobial
3
activity against the bacteria Escherichia coli and Staphylococcus aureus and fungi Aspergillus niger
and Helminthosporium oryzae by comparison with the standard bactericide penicillin and standard

Molecules 2014, 19
13099
fungicide griseofulvin at three different concentrations (100, 50, 25 ppm). The tubes were incubated
aerobically at 37 °C for 18–24 h. The experiments were run in triplicate and the average results are
reported in Table 4. Escherichia coli, Staphylococcus aureus, Aspergillus niger and Helminthosporium
oryzae are shown in Figures 1–4.
Figure 1. Escherichia coli.
Figure 2. Staphylococcus aureus.
Figure 3. Aspergillus niger.

Molecules 2014, 19
13100
Figure 4. Helminthosporium oryzae.
4
. Conclusions
In summary, we have demonstrated a novel methodology based on the Pechmann condensation for
the synthesis of substituted coumarins under solvent-free microwave irradiation conditions, catalyzed
by FeF as an effective eco-friendly catalyst. Moderate to high yields of the corresponding coumarins
3
were obtained. The unique advantages of this method include a one-pot synthesis strategy,
experimental simplicity under solvent-free microwave irradiation, high yields obtained under short
reaction times, easy and quick isolation of the products. The majority of the compounds 1–14 exhibited
significant activity against selected bacteria and fungi with inhibition zones almost comparable to
those of the standard drugs. Thus a new group of compounds with comparable antimicrobial potency
to some presently used commercial bactericides/fungicides has been discovered.
Acknowledgments
We gratefully acknowledge the financial support from the Research Council of Tonekabon Branch
Islamic Azad University.
Author Contributions
Farhad Hatamjafari designed the study, carried out the synthesis and edited the English language.
Vahid Vahabi wrote some research and did the experiments.
Conflicts of Interest
The authors declare no conflict of interest.
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2014 by the authors; licensee MDPI, Basel, Switzerland. This article is an open access article
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