Samarium(III) catalyzed one-pot construction of coumarins

Article abstract of DOI:10.1016/j.tetlet.2004.09.013

Samarium(III) nitrate hexahydrate as a catalyst is used as an alternative to conventional acid catalysts in the von Pechmann condensation of phenols with ethyl acetoacetate leading to the formation of coumarin derivatives.

Full text of DOI:10.1016/j.tetlet.2004.09.013

Tetrahedron
Letters
Tetrahedron Letters 45 (2004) 7999–8001
Samarium(III) catalyzed one-pot construction of coumarins
Sushilkumar S. Bahekara and Devanand B. Shindeb,*
aDepartment of Chemistry, National Cheang Kung University, Tainan, Taiwan
bDepartment of Chemical Technology, Dr. Babasaheb Ambedkar Marathwada University, Aurangabad 431004 (MS), India
Received 30 June 2004; revised 21 August 2004; accepted 2 September 2004
Abstract—Samarium(III) nitrate hexahydrate as a catalyst is used as an alternative to conventional acid catalysts in the von Pech-
mann condensation of phenols with ethyl acetoacetate leading to the formation of coumarin derivatives.
Ó 2004 Elsevier Ltd. All rights reserved.
Coumarins occupy an important place in the realm of
natural products and synthetic organic chemistry. They
have been used as anticoagulants,1 additives in food and
cosmetics,2 and in the preparation of insecticides, optical
Pechmann condensation using Sm(III) as the catalyst
under solvent-free conditions as shown in Scheme 1.
This is a novel, one-pot condensation that not only pre-
serves the simplicity of the Pechmann condensation
reaction but also consistently produces excellent yields
of the coumarin derivatives19 and greatly decreases envi-
ronmental pollution. In the presence of Sm(NO3)3Æ6H2O
(10mol%) the reaction of ethyl acetoacetate (1, 1mmol),
resorcinol (2a, 1mmol) was carried outin one-potreac-
tion under solvent-free conditions for 20min at 80°C,
and resulted in the formation of 7-hydroxy-4-methyl-
coumarin in 98% yield. A wide range of structurally var-
ied phenols reacted smoothly and very quickly to give
4
brighteners,3 and dispersed fluorescentand laser dyes.
Coumarins have synthesized by several methods includ-
ing the von Pechmann,5 Perkin,6 Knoevenagel,7,8 Refor-
mastsky,9 and Wittig10,11 reactions.
The Pechmann reaction is the most widely applied
method for synthesizing coumarins as it involves the
condensation of phenols with b-ketonic esters in the
presence of a variety of acidic condensing agents and
gives good yields of 4-substituted coumarins.12,13
Several acid catalyst have been used in the Pechmann
reaction5 including sulfuric acid,5 phosphorus pentox-
ide,14,15 aluminum chloride,16 trifluoroacetic acid,17
and many more.12 However, these catalysts have to be
used in excess, for example sulfuric acid, 10–12equiv,13
trifluoroacetic acid, 3–4equiv.17 Further the disposal
of acidic waste leads to environmental pollution. The
Pechmann reaction has been carried out successfully
using microwave irradiation18,19 and in ionic liquids20
as alternatives to conventional methods.
OH
O
O
R
OEt
2
1
Sm(NO3)3.6H2O
(10 mol%)
In recentyears, Sm(III) has been used as an efficient
Lewis acid for various transformations such as carbon–
carbon bond formation,21 aldol condensations,22 and
b-diketone and a-selenoketone synthesis.23,24 In this
letter we report a general and practical route25 for the
O
O
R
Keywords: Coumarins; Pechmann condensation; Lewis acid catalysts.
*
3
Corresponding author. Tel.: +91 0240 2401831; fax: +91 0240
2401833; e-mail: ssbahekar@rediffmail.com
Scheme 1.
0040-4039/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2004.09.013

8000
S. S. Bahekar, D. B. Shinde / Tetrahedron Letters 45 (2004) 7999–8001
Table 1. Synthesis of coumarins via von Pechmann condensation of phenols with b-ketoesters catalyzed by Sm(NO3)3Æ6H2O
Entry
1
Phenol 2
Timec (min)
Product 3a,d
MP
Yieldsb (%)
OH
OH
HO
O
O
20
185–187
18527
98
OH
O
O
2
3
4
25
15
25
160–162
161–16226
94
89
95
O
O
O
O
257–258
258–25918
HO
OH
OH
HO
OH
O
O
281–283
280–28527
HO
HO
OH
OH
OH
OH
HO
O
O
O
O
5
20
236–239
236–23828
92
OH
HO
6
7
30
90
138–139
137–13917
90
50
HO
OH
OH
O
O
78–80
8226
OH
8
9
60
40
154–156
15527
85
45
O
O
O
O
O
OH
O
163–164
164–16527
O
OH
OH
O
O N
2
10
20
151–154
150–15118
75
O
N
2
OH

S. S. Bahekar, D. B. Shinde / Tetrahedron Letters 45 (2004) 7999–8001
8001
Table 1 (continued)
Entry
Phenol 2
Timec (min)
Product 3a,d
NO
MP
Yieldsb (%)
2
OH
O
O
11
35
183–185
184–18618
70
NO
2
a All products were characterized by comparison of their mp, IR, and 1H NMR spectra with those of authentic samples.
b Isolated yields.
c All reactions refluxed at 80°C.
d Elemental analyses ( 0.4% of the calculated values) were obtained for all compounds.
11. Yavari, I.; Hekmat-Shoar, R.; Zonouzi, A. Tetrahedron
Lett. 1998, 39, 2391.
the corresponding coumarins in high yield and purity as
listed in Table 1. Many pharmacologically relevantsub-
stitution patterns on the aromatic ring could be intro-
duced with high efficiency, and most importantly,
phenols carrying either electron-donating or electron-
withdrawing substituents all reacted very well, giving
moderate to excellent yields with high purities.
12. Sethna, S.; Phadke, R. Org. React. 1953, 7, 1.
13. Russell, A.; Frye, J. R. Org. Synth. 1941, 21, 22.
14. Simmonis, H.; Remmert, P. Chem. Ber. 1914, 47, 2229.
15. Robertson, A.; Sandrock, W. F.; Henry, C. B. J. Chem.
Soc. 1931, 2426.
16. Sethna, S. M.; Shah, N. M.; Shah, R. C. J. Chem. Soc.
1938, 228.
To study the substituent effects on the reactivity of the
phenol, the reaction was performed on a variety of
phenols. The reaction worked well and the results are
illustrated in Table 1. For most of the substrates, the
reaction time was reduced drastically even at ambient
conditions in contrast to reported procedures12,13 and
gave an excellent yield of the coumarins. Substrates
having electron-donating groups para to the site of elec-
trophilic substitution gave maximum yields in the mini-
mum time.
17. Woods, L. L.; Sapp, J. J. Org. Chem. 1962, 27, 3703.
18. de la Hoz, A.; Moreno, A.; Vaꢀzquez, E. Synlett 1999, 608.
19. Freꢀre, S.; Thieꢀry, V.; Besson, T. Tetrahedron Lett. 2001,
42, 2791.
20. Potdar, M. K.; Mohile, S. S.; Salunkhe, M. M. Tetra-
hedron Lett. 2001, 42, 9285.
21. Yu, Y.; Lin, R.; Zhang, Y. Tetrahedron Lett. 1993, 34,
4547.
22. Bao, W.; Zhang, Y.; Wang, J. Synth. Commun. 1996, 26,
3025.
23. Ying, T.; Bao, W.; Zhang, Y. Synth. Commun. 1996, 26,
2905.
24. Ying, T.; Bao, W.; Zhang, Y. Synth. Commun. 1996, 26,
1517.
In conclusion, we have developed25 a novel and simple
modification of the von Pechmann condensation reac-
tion using Sm(NO3)3Æ6H2O as the catalyst under sol-
vent-free conditions.
25. Typical experimental procedure: A mixture of resorcinol
(1.1g, 10mmol) and ethyl acetoacetate (1.3g, 10mmol)
was heated under reflux in the presence of
Sm(NO3)3Æ6H2O (10mol%) for 20min on 80°C (TLC)
under nitrogen. The reaction mixture, after being cooled
to room temperature, was poured onto crushed ice (40g)
and stirred for 5–10min. The crystalline products were
collected by filtration under suction (water aspirator),
washed with ice-cold water, and then recrystallized from
hot ethanol to afford pure 7-hydroxy-4-methylcoumarin
References and notes
1. Singer, L. A.; Kong, N. P. J. Am. Chem. Soc. 1966, 88, 5213.
2. OꢀKennedy, R.; Thornes, R. D. Coumarins: Biology,
Applications and Mode of Action; Wiley & Sons: Chich-
ester, 1997.
1
3a27 as colorless prisms (1.73g, 98%), mp 185–187°C. H
3. Zahradnik, M. The Production and Application of Fluo-
rescent Brightening Agents; Wiley & Sons, 1992.
4. Murray, R. D. H.; Mendez, J.; Brown, S. A. The Natural
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5. von Pechmann, H.; Duisberg, C. Chem. Ber. 1884, 17, 929.
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10. Narasimahan, N. S.; Mali, R. S.; Barve, M. V. Synthesis
1979, 906.
NMR (CDCl3) 2.2 (s, 3H, –CH3), 6.1 (s, 1H), 6.83 (d, 1H),
6.97 (s, 1H), 7.5 (d, 1H); IR (KBr) 2985, 1740, 1625cm.
This procedure was followed for the preparation of all the
substituted coumarins listed in Table 1. All the com-
pounds were identified by comparison of analytical data
(IR, 1H NMR, and mass spectra) and mpꢀs with those
reported.
26. Abram, N. B.; Jack, D.; William, L. W. J. Med. Chem.
1986, 29, 1094.
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D. J.; Kontogiorgis, C. A.; Litinas, K. E.; Nicolaides,
D. N. J. Chem. Soc., Perkin Trans. 1 2001, 3073.