A practical one-pot synthesis of coumarins in aqueous sodium bicarbonate via intramolecular Wittig reaction at room temperature

Article abstract of DOI:10.1039/c4ra06996j

An efficient, simple and relatively inexpensive method for the synthesis of coumarins in aqueous sodium bicarbonate at ambient temperature has been developed. It features an intramolecular Wittig reaction of substituted 2-formylphenyl 2-bromoacetate in saturated aqueous sodium bicarbonate. Its advantages include benign reaction conditions, easy work-up and good overall yield with short reaction time. Various substituted coumarins have been synthesized by utilizing this methodology. This journal is

Full text of DOI:10.1039/c4ra06996j

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A practical one-pot synthesis of coumarins in
aqueous sodium bicarbonate via intramolecular
Wittig reaction at room temperature†
Cite this: RSC Adv., 2014, 4, 39667
Ningaraddi S. Belavagi, Narahari Deshapande, Manjunath G. Sunagar
and Imtiyaz Ahmed M. Khazi*
An efficient, simple and relatively inexpensive method for the synthesis of coumarins in aqueous sodium
bicarbonate at ambient temperature has been developed. It features an intramolecular Wittig reaction of
substituted 2-formylphenyl 2-bromoacetate in saturated aqueous sodium bicarbonate. Its advantages
include benign reaction conditions, easy work-up and good overall yield with short reaction time.
Various substituted coumarins have been synthesized by utilizing this methodology.
Received 11th July 2014
Accepted 19th August 2014
DOI: 10.1039/c4ra06996j
www.rsc.org/advances
13
Pechmann reactions and more recently palladium-catalyzed
carbonylative annulations.
Notably, most of the methods for the synthesis of coumarins
Introduction
14
Solvent free organic reactions and reactions in aqueous
conditions have greatly inuenced and attracted the chemist's reported to date have been developed without attention to its
1,2
interest as an integral part of green chemistry. Recently these environmental impact, making the development of new reliable
reactions without the use of harmful organic solvents have high-yielding eco-friendly methods for the synthesis of
drawn much more attention. Use of water as a medium for coumarins an important subject. The intramolecular Wittig
organic reactions has a large number of desired advantages as reaction has been extensively used as an excellent method for
it is a cost-effective, non-toxic, non-hazardous and environ- the C–C bond-forming process in the synthesis of natural
15
mentally benign solvent where isolation of the organic prod- products. The rst synthesis of coumarin via intramolecular
3
16
ucts can be performed by simple phase separation. A wide Wittig reaction was reported as a short paper by Desai et al.
range of stabilized ylides and aldehydes have been extensively wherein they have used toxic chloroform and pyridine and
used in aqueous media during the Wittig reaction as an failed to isolate any intermediates and obtained the product in
important carbon–carbon bond forming reaction. Despite, the very low yield (26–30%).
poor solubility of reactants, acceptable yields are obtained and
the rate of the reactions in water is unexpectedly accelerated as
Results and discussion
it lowers the energy of the transition state for the Wittig
4
reaction.
During the course of our investigation to develop novel
The coumarin scaffold and its derivatives exhibit diverse greener synthetic methods for the synthesis of biologically
biological and pharmaceutical properties such as anti-HIV, active heterocyclic compounds, we herein report an efficient,
anticoagulant, antibacterial, antioxidant and anticancer are simple and relatively inexpensive method for the synthesis of
5,6
well known. Some of them also display a broad range of coumarins via intramolecular Wittig reaction under very
applications as additives to perfumes and cosmetics, as mild and environmentally benign conditions: in saturated
photographic sensitizers and solar collectors, as uorescent aqueous sodium bicarbonate and at ambient temperature
7,8
markers in biochemistry and as tunable dye lasers. Because of (Scheme 1). The main objective of this work was to explore
the signicance of this heterocyclic system and their diverse the synthesis of coumarin derivatives in aqueous media via
pharmacological properties, many strategies for the synthesis of the intramolecular Wittig reaction.
substituted coumarins have been developed, which include
Based on the concept of preparing phosphoranes in situ
9
10
11
12
Perkin,
Wittig,
Knoevenagel,
Reformatsky,
and during the Wittig process, we attempted the one pot
synthesis of coumarin via intramolecular Wittig reaction in
saturated aqueous sodium bicarbonate, which proceeded in
decent yields with short reaction time (20–30 min).
In order to establish the optimal reaction conditions in terms
of various organic and inorganic bases in water media, the Wittig
salt 3a was chosen as model substrate. As shown in Table 1,
Karnatak University, Department of Chemistry, Dharwad-580003, Karnataka, India.
E-mail: drimkorgchem@gmail.com
†
Electronic supplementary information (ESI) available. See DOI:
0.1039/c4ra06996j
1
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Scheme 1 Aqueous sodium bicarbonate mediated synthesis of coumarins via intramolecular Wittig reaction at room temperature.
various organic bases, such as triethylamine, pyridine, piperi- product, this might be due to strong alkali (pH ¼ 12) nature of
dine, DBU and DMAP have been applied to promote this model saturated Na
2
CO
3
which might be cleaving the coumarin ring.
ꢀ
reaction in water at 25 C, only low yields (12–20%) of the desired
The reaction with saturated NaHCO at elevated temperature
3
product 4a were obtained (Table 1, entries 1–5). The reaction was (Table 1, entries 14) resulted in the decomposition of the
then carried out with various inorganic bases, such as NaOH, formed product due to dehydration of NaHCO3 to Na CO ,
2
3
KOH, Na CO , K CO and NaHCO which again afforded the which increases the basicity of the reaction media resulting in
2
3
2
3
3
desired product 4a in low yield at room temperature (Table 1, the cleavage of coumarin ring.
entries7–9).Longerreactiontimeandhighertemperaturedidnot
Among all the bases evaluated in water, saturated aqueous
3
further promote the reaction (Table 1, entries 11). Only a trace NaHCO mediated intramolecular Wittig reaction afforded the
amount of the desired product was obtained when the reaction coumarin 4a in decent yield with short reaction time (20–30 min)
ꢀ
was conducted in pure water without a base at 80 C for 8 h (Table at room temperature. The remarkable activation in the reaction
1, entry 13). When we carried out the reaction in saturated rate is due to, lowering of energy of the transition state for the
aqueous NaHCO , to our delight 4a was produced in 70% yield Wittig reaction by saturated aqueous sodium bicarbonate. This
3
with short reaction time (30 min) at room temperature (Table 1, prompted us to explore the potential of this protocol for the
entries 12). In saturated Na CO solution the product yield was synthesis of various coumarin derivatives.
2
3
lowered to 18% (Table 1, entry 15) and stirring for longer time in
Encouraged by this promising result, the substrate scope was
saturated Na
2
CO
3
resulted in decomposition of the formed further extended to a variety of substituted 2-formylphenyl 2-
a
Table 1 Optimization of base, time and temperature in water for the synthesis of coumarin 4a via intramolecular Wittig reaction
a
Entry
Solvent
Base (equivalent)
Time (min)
Temperature
Yield (%)
ꢀ
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
Water
Water
Water
Water
Water
Water
Water
Water
Water
Water
Water
Water
Water
Water
Water
Triethylamine (2.2)
Pyridine (2.2)
Piperidine (2.2)
DBU (2.2)
DMAP (2.2)
NaOH (2.2)
300
300
300
300
300
300
300
300
300
300
8 h
30
25 C
10
12
12
22
18
18
15
25
28
30
30
70
Trace
20
18
ꢀ
25 C
ꢀ
25 C
ꢀ
25 C
ꢀ
25 C
ꢀ
25 C
ꢀ
KOH (2.2)
25 C
ꢀ
Na
CO
NaHCO
Na CO
2
CO
3
(2.2)
(2.2)
25 C
ꢀ
K
2
3
25 C
ꢀ
0
1
2
3
4
5
3
(2.2)
(5.0)
25 C
ꢀ
2
3
85 C
ꢀ
NaHCO
—
3
(saturated)
25 C
ꢀ
8 h
20
30
85 C
ꢀ
NaHCO
3
(saturated)
60 C
ꢀ
Na
2
CO
3
(saturated)
25 C
a
Isolated yield aer column purication.
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Table 2 Synthesis of coumarins (4a–h) under optimized conditions
a
b
c
Entry
Substrates (2a–h)
Wittig salt (3a–h)
Products (4a–h)
Time (min)
Yield (%)
1
30
30
70
68
2
3
4
5
30
30
25
68
72
75
6
7
30
30
72
72
8
30
70
a
ꢀ
Wittig salts (3a–h) were obtained in quantitative yields in 2 h at 60 C and used immediately for the second step reaction because of their
b
c
hygroscopic nature. Time required for step-2. Overall isolated yield aer column purication.
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bromoacetates (2a–h) (Table 2). As is apparent from Table 2, the on Bruker 300 MHz and 400 MHz FT NMR spectrometer in
reaction is highly versatile and efficient with various substitu- CDCl and DMSO-d by using TMS as internal standard.
3
6
ents such as chloro (2b), bromo (2c), methyl (2d), methoxy (2e),
N,N-dimethyl (2f) and N,N-diethyl (2g) which yielded the corre- Typical procedure for the synthesis of 2H-chromen-2-one (4a)
sponding coumarins 4a–h in 65–75% yield.
Further to test the feasibility of a large-scale reaction, the
reaction of 4-bromo-2-formylphenyl 2-bromoacetate (2c)
A mixture of 2-formylphenyl 2-bromoacetates 2a (2 mmol, 0.5 g)
and triphenylphosphine (2 mmol, 0.55 g) in ethyl acetate (5 mL)
ꢀ
was stirred at 60 C for 2 h. The progress of the reaction was
(31 mmol) and triphenylphosphine (31 mmol) was investigated.
monitored by TLC (eluent: EtOAc–hexane, 2 : 8). Aer comple-
tion of the reaction, the mixture was cooled to room tempera-
ture and the separated Wittig salt 3a was ltered and washed
with cold ethyl acetate (5 mL). The obtained Wittig salt 3a
The reaction could afford 4.6 g of 4c in 65% yield aer column
purication. Hence, this protocol could be used as a practical
method to synthesize the bioactive coumarins.
The required substituted 2-formylphenyl 2-bromoacetates
3
(2 mmol, 1.0 g) was taken in saturated aqueous NaHCO (5 mL)
(
2a–h) were readily obtained by modication of a literature
and stirred vigorously for 30 min at room temperature. The
progress of the reaction was monitored by TLC (eluent: EtOAc–
hexane, 2 : 8). Aer completion of the reaction, the crude
reaction mixture was extracted with ethyl acetate (3 ꢁ 10 mL),
17
method from substituted salicylaldehydes and bromoacetyl
bromide in THF/NaH at 0 C. Aer work-up, the 2-formylphenyl
ꢀ
2-bromoacetates (2a–h) were obtained in 80–90% yield with
sufficient purity which can be directly used for the next step
reaction. These aldehydes (2a–h) were converted to the corre-
sponding Wittig salts (3a–h) by reacting with triphenylphos-
the combined organic layer was washed with H
2
O (10 mL) and
dried over Na SO . The solvent was evaporated under reduced
2 4
pressure and the residue was puried by column chromatog-
raphy on silica (60–120, eluent: EtOAc–hexane, 2 : 8) to afford
the pure products in 65–75% yields (Table 2). The physical data
ꢀ
phine in ethylacetate for 2 h at 60 C in quantitative yields. Since
these Wittig salts were hygroscopic, they were immediately used
for the one-pot synthesis of coumarins (4a–h) via intra-
molecular Wittig reaction in saturated aqueous sodium bicar-
bonate. The products were isolated by simple extraction with
ethylacetate and puried by column chromatography on silica.
The reactions of salicylaldehydes having electron-donating
groups furnished slightly greater yields of coumarins
compared to that without electron-donating groups or with an
electron-withdrawing group. However the reaction of 5-nitro
salicylaldehyde with bromoacetyl bromide did not proceed
because of the strong electron withdrawing nature of the nitro
group. Similarly 3,5-dichloro salicylaldehyde did not react with
bromoacetyl bromide because of steric hindrance of 3-chloro
substituent.
(mp, NMR) of all the known compounds were found to be
identical with those reported in the literature.
18
2H-Chromen-2-one (4a)
ꢀ
Yield: 0.210 g (70%); white solid; mp: 68–69 C. IR (KBr): 1696,
ꢂ1
1
1
602, 1383, 1237, 1067, 985, 856, 758, 572, 525, 426 cm . H
NMR (400 MHz, CDCl
3
): d 7.70 (d, J ¼ 9.6 Hz, 1H), 7.56–7.48 (m,
1
3
2H), 7.35–7.26 (m, 2H), 6.42 (d, J ¼ 9.6 Hz, 1H); C NMR (400
3
MHz, CDCl ): d 161.2, 154.4, 143.9, 132.3, 128.3, 124.8, 119.2,
117.3, 117.1.
19
6-Chloro-2H-chromen-2-one (4b)
ꢀ
Yield: 0.221 g (68%); colorless solid; mp: 152–153 C. IR (KBr):
1
5
7
1
1
699, 1602, 1383, 1237, 1067, 950, 895, 830, 820, 730, 590, 530,
Conclusion
ꢂ1
1
00 cm ; H NMR (400 MHz, CDCl ): d 7.56 (d, J ¼ 9.6 Hz, 1H),
3
In conclusion, we have developed an efficient, simple and
relatively inexpensive one-pot method for the synthesis of
coumarins via intramolecular Wittig reaction in saturated
.41–7.43 (m, 2H), 7.21 (d, J ¼ 7.0 Hz, 1H), 6.39 (d, J ¼ 9.6 Hz,
1
3
H). C NMR (400 MHz, CDCl ): d 159.5, 151.9, 141.7, 131.3,
3
29.2, 126.6, 119.3, 117.8, 117.3.
3
aqueous NaHCO at room temperature. The methodology offers
several advantages such as using green solvent, one-pot
manner, ambient temperature, high reaction rates, good
yields and simplicity in the extraction of the product, which
make it a useful and attractive strategy in the synthesis of
various substituted coumarins.
20
6
-Bromo-2H-chromen-2-one (4c)
ꢀ
Yield: 0.237 g (68%); light brownish solid; mp: 162–164 C. IR
KBr): 1690, 1600, 1383, 1237, 1067, 950, 895, 830, 730, 620, 590,
30, 500 cm . H NMR (400 MHz, CDCl
.15 (d, J ¼ 7.0 Hz, 1H), 6.39 (d, J ¼ 9.6 Hz, 1H). C NMR (400
): d 159.9, 152.9, 142.1, 134.6, 130.2, 120.3, 118.6,
17.8, 116.9.
(
5
7
ꢂ1
1
3
): d 7.53–7.57 (m, 3H),
1
3
MHz, CDCl
1
3
Experimental
General information
21
6-Methyl-2H-chromen-2-one (4d)
All reagents were of analytical grade and were used directly.
ꢀ
Thin-layer chromatography (TLC) was performed on silica gel Yield: 0.224 g (72%); colorless solid; mp: 73–75 C. IR (KBr):
plates (60 F254; Merck). Column chromatography was per- 1717, 1684, 1575, 1380, 1262, 1189, 1167, 1105, 911, 841, 820,
ꢂ1
1
formed using silica (60–120 mesh size; Merck). Melting points 813 cm . H NMR (300 MHz, CDCl ): d 7.69 (J ¼ 9.3 Hz, 1H),
3
1
3
were determined in open capillaries and are uncorrected. The 7.40.7.20 (m, 3H), 6.43 (d, J ¼ 9.3 Hz, 1H), 2.43 (s, 3H). C NMR
IR spectra were recorded on Nicolet Impact 410 FT IR spectro- (300 MHz, CDCl ): d 161.0, 152.0, 143.4, 134.1, 132.8, 127.6,
photometer using KBr pellets. H and C NMR were recorded 118.5, 116.5, 116.4, 20.7.
3
1
13
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2
1
6
-Methoxy-2H-chromen-2-one (4e)
3 (a) F. Bigi, L. Chesini, R. Maggi and G. Sartori, J. Org. Chem.,
1994, 64, 1033–1035; (b) F. Bigi, M. L. Conforti, R. Maggi,
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ꢀ
Yield: 0.242 g (75%); colorless solid; mp: 100–102 C. IR (KBr):
ꢂ1
1
1
705, 1570, 1491, 1451, 1286, 1261, 1185, 886, 808, 684 cm . H
NMR (300 MHz, CDCl
): d 7.64 (d, J ¼ 9.6 Hz, 1H), 7.22 (d, J ¼ 9.0
Hz, 1H), 7.07 (dd, J ¼ 9.0, 2.7 Hz, 1H), 6.89 (d, J ¼ 2.7 Hz, 1H),
4
A. El-Batta, C. Jiang, W. Zhao, R. Anness, A. L. Cooksy and
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3
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6
.35 (d, J ¼ 9.9 Hz, 1H), 3.82 (s, 3H). C NMR (300 MHz, CDCl
3
):
7
d 160.9, 155.9, 148.3, 143.2, 119.4, 119.0, 117.7, 116.9, 109.9,
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5
5.7.
22
7-(Dimethylamino)-2H-chromen-2-one (4f)
6
ꢀ
Yield: 0.238 g (72%); purple powder; mp: 161–162 C. IR (KBr):
ꢂ1
1
1
685, 1570, 1491, 1451, 1286, 1261, 1185, 886, 808, 684 cm . H
NMR (300 MHz, CDCl
): d 7.54 (d, J ¼ 9.3 Hz, 1H), 7.25 (d, J ¼ 2.8
Hz, 1H), 6.61 (dd, J ¼ 8.7 Hz, 2.3 Hz, 1H), 6.49 (d, J ¼ 2.2 Hz, 1H),
3
6
2
14; (c) M. L. Go, X. Wu and X. L. Liu, Curr. Med. Chem.,
005, 12, 483–499.
1
3
6
.06 (d, J ¼ 9.3 Hz, 1H), 3.82 (s, 3H), 2.9 (s 6H). C NMR (300
MHz, CDCl ): d 162.1, 156.3, 152.9, 143.7, 128.5, 109.8, 109.0,
08.8, 98.1, 40.2.
3
7
8
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976, 70, 258–262.
1
2
23
7
-(Diethylamino)-2H-chromen-2-one (4g)
1
ꢀ
Yield: 0.248 g (72%); yellowish powder; mp: 93–95 C. IR (KBr):
1
9 B. J. Donnelly, D. M. Donnelly and A. M. O'Sullivan,
Tetrahedron, 1968, 24, 2617–2622.
ꢂ1
1
680, 1570, 1491, 1451, 1286, 1261, 1185, 886, 808, 684 cm . H
NMR (400 MHz, CDCl ): d 7.45 (d, J ¼ 9.2 Hz, 1H), 7.13 (d, J ¼ 2.4 10 I. Yavari, R. Heckmat-Shoar and A. Zonouzi, Tetrahedron
3
Hz, 1H), 6.48 (d, J ¼ 8.8 Hz, 1H), 6.42 (d, J ¼ 2.0 Hz, 1H), 5.95 (d,
Lett., 1998, 39, 2391–2392.
J ¼ 9.2 Hz, 1H), 3.33 (q, J ¼ 14.2 Hz, 4H), 1.14 (t, J ¼ 6.8 Hz, 6H). 11 (a) F. Bigi, L. Chesini, R. Maggi and G. Sartoni, J. Org. Chem.,
1
3
C NMR (400 MHz, CDCl
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1999, 64, 1033–1035; (b) F. Fringuelli, O. Piermatti and
F. Pizzo, Synthesis, 2003, 15, 2331–2334; (c) J. R. Harjini,
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1127–1130.
109.1, 108.6, 108.3, 97.5, 44.7, 12.4.
24
3H-Benzo[f]chromen-3-one (4h)
ꢀ
12 S. Palaniappan and R. C. Shekhar, J. Mol. Catal. A: Chem.,
2004, 209, 117–214.
Yield: 0.234 g (70%); yellowish powder; mp: 117–119 C. IR
(
ꢂ1
1
KBr): 1705, 1278, 1257, 1200, 1119 cm . H NMR (400 MHz,
1
3 (a) V. Singh, S. Kaur, V. Sapehiya, J. Singh and G. L. Kad,
Catal. Commun., 2005, 6, 57–60; (b) J. Fraga-Dubreuil,
J. P. Bazureau and J. Hamelin, J. Heterocycl. Chem., 2007,
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3
J ¼ 9.0 Hz, 1H), 7.90 (d, J ¼ 8.1 Hz, 1H), 7.71–7.66 (m, 1H), 7.59–
1
3
7
.54 (m, 1H), 7.44 (d, J ¼ 9.2 Hz, 1H), 6.56 (d, J ¼ 9.8 Hz, 1H).
C
4
4, 193–199.
4 D. V. Kadnikov and R. C. Larock, J. Org. Chem., 2003, 68,
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5 (a) B. M. Heron, Heterocycles, 1995, 41, 2357–2386; (b)
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3
NMR (400 MHz, CDCl ): d 160.9, 153.9, 139.1, 133.1, 130.3,
1
1
129.0, 128.3, 126.1, 121.3, 117.1, 115.6, 113.0.
9
Acknowledgements
1999, 1, 3049–3066.
The authors gratefully acknowledge the nancial assistance
1
1
1
1
2
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project no. SR/S1/OC-58/2011. One of the authors NSB thank
Sigma-Aldrich Chemicals Private Limited, Bangalore India for
technical support.
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