Next Article in Journal
Hyperspectral Imaging and Chemometric Modeling of Echinacea — A Novel Approach in the Quality Control of Herbal Medicines
Previous Article in Journal
Synthesis and Biological Evaluation of New Pyridone-Annelated Isoindigos as Anti-Proliferative Agents
Open AccessArticle

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

by Vahid Vahabi *,† and Farhad Hatamjafari
Department of Chemistry, Faculty of Science, Islamic Azad University-Tonekabon Branch, Tonekabon 46841-61167, Iran
*
Author to whom correspondence should be addressed.
These authors contributed equally to this work.
Molecules 2014, 19(9), 13093-13103; https://doi.org/10.3390/molecules190913093
Received: 30 June 2014 / Revised: 4 August 2014 / Accepted: 11 August 2014 / Published: 26 August 2014
(This article belongs to the Section Organic Chemistry)

Abstract

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.
Keywords: coumarin; solvent-free; FeF3; one-pot; microwave irradiation; antimicrobial activities coumarin; solvent-free; FeF3; one-pot; microwave irradiation; antimicrobial activities

1. Introduction

Coumarin and its derivatives are biologically and pharmacologically active compounds with a wide 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 [5,6,7]. 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 [9,10,11,12], phase transfer catalysts [13,14,15,16,17], 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 FeF3 to the current process is demonstrated in comparison with other Lewis acids, 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 [27,28,29,30,31,32,33,34,35,36]. 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 Pechmann condensation using FeF3 as a catalyst under solvent-free microwave irradiation (Scheme 1).
Scheme 1. FeF3 catalyzed Pechmann reaction.
Scheme 1. FeF3 catalyzed Pechmann reaction.
Molecules 19 13093 g005

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.
Table 1. FeF3 catalyzed synthesis of coumarin derivatives a.
Table 1. FeF3 catalyzed synthesis of coumarin derivatives a.
EntryPhenolProductTime (min)Yield (%)MP °C, (Lit) [ref.]
1 Molecules 19 13093 i001 Molecules 19 13093 i00289780–82, (81) [37]
2 Molecules 19 13093 i003 Molecules 19 13093 i004998132–135, (131–133) [9]
3 Molecules 19 13093 i005 Molecules 19 13093 i006993172–174, (171–172) [9]
4 Molecules 19 13093 i007 Molecules 19 13093 i008795185–188, (184–185) [9]
5 Molecules 19 13093 i009 Molecules 19 13093 i010794258–260, (257–260) [38]
6 Molecules 19 13093 i011 Molecules 19 13093 i012889135–138, (137–138) [37]
7 Molecules 19 13093 i013 Molecules 19 13093 i014790235–236, (234–237) [37]
8 Molecules 19 13093 i015 Molecules 19 13093 i016692281–284, (280–281) [9]
9 Molecules 19 13093 i017 Molecules 19 13093 i018693165–170, (169–170) [9]
10 Molecules 19 13093 i019 Molecules 19 13093 i020787176–180, (180–182) [9]
11 Molecules 19 13093 i021 Molecules 19 13093 i022885153–156, (154–155) [9]
12 Molecules 19 13093 i023 Molecules 19 13093 i024961165–169
13 Molecules 19 13093 i025 Molecules 19 13093 i026871160–162
14 Molecules 19 13093 i027 Molecules 19 13093 i028966168–170
a Reaction conditions: phenols (1 mmol), ethyl acetoacetate(1 mmol), FeF3 (0.05 g), Isolated yield.
In this research, we have synthesized some coumarins derivatives using phenols and ethyl acetoacetate in the presence of FeF3 as a catalyst to create the corresponding products, as illustrated in 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 results presented in this table, FeF3 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 products were characterized by using melting points, infrared spectroscopy (IR), proton nuclear magnetic resonance spectroscopy (1H-NMR), carbon-13 nuclear magnetic resonance spectroscopy (13C-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. FeF3 catalyzed synthesis of 7-hydroxy-4-methyl-chromen-2-one (4) in various amount of the catalyst under solvent-free microwave irradiation a.
Table 2. FeF3 catalyzed synthesis of 7-hydroxy-4-methyl-chromen-2-one (4) in various amount of the catalyst under solvent-free microwave irradiation a.
NO.Catalyst (g)Yield (%)
1-15
20.0269
30.0486
40.0595
50.0691
60.0789
70.0887
80.1085
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 (1 mmol), ethyl acetoacetate (1 mmol), and FeF3 (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. FeF3 catalyzed synthesis of 7-hydroxy-4-methyl-chromen-2-one (4) under various solvent and solvent-free conditions.
Table 3. FeF3 catalyzed synthesis of 7-hydroxy-4-methyl-chromen-2-one (4) under various solvent and solvent-free conditions.
NO.SolventYield (%)
1solvent-free95
2DMF57
3acetonitrile63
4dichloromethane49
5water64
6ethanol81
7methanol80
8dioxane74
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. FeF3 was reused for four runs without 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.
Table 4. Reaction of resorcinol with ethyl acetoacetate (Table 1, Entry 4) in the presence of different catalysts.
EntryCatalyst/mol%ConditionsReaction Time (min)Yield (%)Reference
1Ce(OTf)4/1H2O/Room Temperature1592[39]
2PFPAT/10Toluene/110 °C18090[39]
3MFRH/0.05 gSolvent free/80 °C5065[39]
4Oxalic acid/10Solvent free/80 °C3095[39]
Nanoreactors/7Solvent free/130 °C6030[39]
5FeF3/0.05 gHeating/Ethanol, reflux12067This Research
5FeF3/0.05 gMicrowaves795This Research
All the title compounds 114 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 114 (µg/mL).
Table 5. Antimicrobial activity of the compounds 114 (µg/mL).
CompoundZone of Inhibition (%)
Antibacterial ActivityAntifungal Activity
Escherichia coliStaphylococcus aureusAspergillus nigerHelminthosporium oryzae
1005025100502510050251005025
12110522106201071385
222116211051812619127
32312723126191381374
420127211052111719107
52211621126181161374
62210622127199418105
724148231272114820158
82110522115201241495
921117211252012619107
1023128231062113620116
1121105201062010519116
1223137231282012720105
132210521106191151686
142211522105201141595
Penicillin Griseofulvin20128201282010520105

3. Experimental Section

3.1. General Information

Melting points were measured on an Electrothermal 9100 apparatus. All reactions were carried out in a CEM MARS 5TM microwave oven. The TLC was performed with silica gel SILG/UV 254 plates. IR spectra were measured using a Shimadzu IR-470 spectrophotometer. 1H- and 13C-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 FeF3 (0.05 g) was ground in an open Pyrex beaker and the homogenized mixture was heated by microwave irradiation for about 7 min, as indicated in Table 1. The progress of the reaction was monitored by using TLC (ethyl 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:
4,5,6,7-Tetramethyl-2H-chromen-2-one (12): Yellow solid; m.p.: 165–169 °C; IR (KBr) νmax (cm−1): 1674 (ester C=O stretch), 1602 (C−C=C stretch); 1H-NMR (DMSO-d6) δ: 2.12 (s, 3H, CH3), 2.20 (s, 3H, CH3), 2.31 (s, 3H, CH3), 2.42 (s, 3H, CH3), 6.25 (m, 1H), 7.24 (s, 1H); 13C-NMR (DMSO-d6) δ: 14.4, 17.6, 21.8, 23.7, 114.5, 117.0, 121.7, 125.6, 131.8, 133.7, 152.1, 158.8. MS (m/z): 202 (M+); Anal. Calcd for C13H14O2: C, 77.30; H, 7.03%. %. Found: C, 77.15; H, 6.86%.
6-Ethyl-4-methyl-2H-chromen-2-one (13): Yellow solid. m.p.: 160–162 °C. IR (KBr) νmax (cm−1): 1666 (ester C=O stretch), 1589 (C−C=C stretch). 1H-NMR (DMSO-d6) δ: 1.85 (t, J = 7.2, 3H, CH3), 2.38 (s, 3H, CH3), 3.63 (q, J = 7.2, 2H, CH2), 5.91 (m, 1H), 7.11 (d, J = 8.5, 1H), 7.34 (dd, J = 8.5, 2.2, 1H), 7.41 (s (br), 1H); 13C-NMR (DMSO-d6) δ: 16.8, 18.8, 22.4, 115.4, 118.6, 123.3, 124.8, 130.9, 135.1, 155.3, 161.2. MS (m/z): 188 (M+). Anal. Calcd for C12H12O2: C, 76.57; H, 6.43%. Found: C, 77.25; H, 6.38%.
6-Isopropyl-4-methyl-2H-chromen-2-one (14): Yellow solid; m.p.: 168–170 °C. IR (KBr) νmax (cm−1): 1658 (ester C=O stretch), 1585 (C−C=C stretch). 1H-NMR (DMSO-d6) δ: 1.65 (d, J = 6.5, 1H, CH), 2.44 (s, 3H, CH3), 2.95 (q, J = 6.5, 6H, 2CH3), 5.89 (m, 1H), 7.15 (d, J = 8.3, 1H), 7.30 (dd, J = 8.3, 2.3, 1H), 7.45 (s (br), 1H); 13C-NMR (DMSO-d6) δ: 14.8, 15.6, 18.5, 24.9, 116.7, 119.2, 122.7, 126.9, 133.4, 137.3, 157.4, 163.5. MS (m/z): 202 (M+). Anal. Calcd for C13H14O2: C, 77.20; H, 6.98%. Found: C, 76.55; H, 6.68%.

3.3. Antimicrobial Activity

The compounds 114 were screened by the disk diffusion method [40,41], for their antimicrobial 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 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 Figure 1, Figure 2, Figure 3 and Figure 4.
Figure 1. Escherichia coli.
Figure 1. Escherichia coli.
Molecules 19 13093 g001
Figure 2. Staphylococcus aureus.
Figure 2. Staphylococcus aureus.
Molecules 19 13093 g002
Figure 3. Aspergillus niger.
Figure 3. Aspergillus niger.
Molecules 19 13093 g003
Figure 4. Helminthosporium oryzae.
Figure 4. Helminthosporium oryzae.
Molecules 19 13093 g004

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 FeF3 as an effective eco-friendly catalyst. Moderate to high yields of the corresponding coumarins 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 114 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.

References

  1. Kostova, I. Synthetic and natural coumarins as cytotoxic agents. Curr. Med. Chem. 2005, 5, 29–46. [Google Scholar]
  2. Al-Amiery, A.A.; Kadhum, A.; Mohamad, A. Antifungal activities of new coumarins. Molecules 2012, 17, 5713–5723. [Google Scholar] [CrossRef]
  3. Bahekar, S.S.; Shinde, D.B. Samarium(III) catalyzed one-pot construction of coumarins. Tetrahedron Lett. 2004, 45, 7999–8001. [Google Scholar] [CrossRef]
  4. Lake, B.G. Coumarin metabolism, toxicity and carcinogenicity: Relevance for human risk assessment. Food Chem. Toxicol. 1999, 37, 423–453. [Google Scholar] [CrossRef]
  5. Zahradnik, M. Production and Application of Fluorescent Brightening Agents; John Wiley & Sons: New York, NY, USA, 1992. [Google Scholar]
  6. Chen, J.; Liu, W.; Ma, J.; Xu, H.; Wu, J.; Tang, X.; Fan, Z.; Wang, P. Synthesis and properties of fluorescence dyes: Tetracyclic pyrazolo[3,4-b]pyridine-based coumarin chromophores with intramolecular charge transfer character. J. Org. Chem. 2012, 77, 3475–3482. [Google Scholar] [CrossRef]
  7. Hadacek, F.; Mueller, C.; Werner, A.; Greger, H.; Proksch, P. Analysis, isolation and insecticidal activity of linear furanocoumarins and other coumarin derivatives from Peucedanum (Apiaceae: Apioideae). J. Chem. Ecol. 1994, 20, 2035–2054. [Google Scholar] [CrossRef]
  8. Weigt, S.; Huebler, N.; Strecker, R.; Braunbeck, T.; Broschard, T.H. Developmental effects of coumarin and the anticoagulant coumarin derivative warfarin on zebrafish (Danio rerio) embryos. Reprod. Toxicol. 2012, 33, 133–141. [Google Scholar] [CrossRef]
  9. Amoozadeh, A.; Ahmadzadeh, M.; Kolvari, E. Easy access to coumarin derivatives using alumina sulfuric acid as an efficient and reusable catalyst under solvent-free conditions. J. Chem. 2013. [Google Scholar] [CrossRef]
  10. Sangshettia, J.N.; Nagnnath, D.; Kokarea, B.; Shinde, D.B. Water mediated efficient one-pot synthesis of bis-(4-hydroxycoumarin)methanes. Green Chem. Lett. Rev. 2009, 2, 233–235. [Google Scholar] [CrossRef]
  11. Narsaiah, A.V.; Nagaiah, K. An efficient Knoevenagel condensation catalyzed by LaCl3·7H2O in heterogeneous medium. Synth. Commun. 2003, 33, 3825–3832. [Google Scholar] [CrossRef]
  12. Lehnert, W. Verbesserte variante der knoevenagel-kondensation mit TiCl4/THF/pyridin(I). Alkylidenund arylidenmalonester bei 0–25 °C. Tetrahedron Lett. 1970, 11, 4723–4724. [Google Scholar] [CrossRef]
  13. Karimi-Jaberi, Z.; Nazarifar, M.R.; Pooladian, B. Tris(hydrogensulfato) boron as a solid heterogeneous catalyst for the rapid synthesis of α,α'-benzylidene bis (4-hydroxycoumarin) derivatives. Chin. Chem. Lett. 2012, 23, 781–784. [Google Scholar] [CrossRef]
  14. Mehrabi, H.; Abusaidi, H. Synthesis of biscoumarin and 3,4-dihydropyrano[c] chromene derivatives catalysed by sodium dodecyl sulfate (SDS) in neat water. J. Iran. Chem. Soc. 2010, 7, 890–894. [Google Scholar] [CrossRef]
  15. Ang, D.O. Hypophosphorous acid mediated dehalogenation in water. Tetrahedron Lett. 1996, 37, 5367–5368. [Google Scholar] [CrossRef]
  16. Yorimitsu, H.; Shinokubo, H.; Oshima, K. Radical cyclization reaction using a combination of phosphinic acid and a base in aqueous ethanol. Chem. Lett. 2000, 2, 104–105. [Google Scholar] [CrossRef]
  17. Kita, Y.; Nambu, H.; Ramesh, N.G.; Anilkumar, G.; Matsugi, M. A novel and efficient methodology for the C−C bond forming radical cyclization of hydrophobic substrates in water. Org. Lett. 2001, 3, 1157–1160. [Google Scholar] [CrossRef]
  18. Cravotto, G.; Nano, G.M.; Palmisano, G.; Tagliapietra, S. The reactivity of 4-hydroxycoumarin under heterogeneous high-intensity sonochemical conditions. Synthesis 2003, 8, 1286–1291. [Google Scholar]
  19. Bansal, K.M.; Mothsra, P.; Saxen, S.; Somvanshi, R.K.; Dey, S.; Singh, T.P. Molecular iodine: A versatile catalyst for the synthesis of bis(4-hydroxycoumarin) methanes in water. J. Mol. Catal. A: Chem. 2007, 268, 76–81. [Google Scholar] [CrossRef]
  20. Johnson, J.R. Other classical coumarins syntheses include the Perkin. In Organic Reactions; John Wiley & Sons: New York, NY, USA, 1942; Volume 1, pp. 210–285. [Google Scholar]
  21. Jones, G. The Knoevenagel Condensation Reaction in Organic Reactions; John Wiley: New York, NY, USA, 1967; Volume 15, pp. 204–599. [Google Scholar]
  22. Shriner, R.L. Reformatsky Reaction. In Organic Reactions; John Wiley & Sons: New York, NY, USA, 1942; Volume 1, pp. 1–37. [Google Scholar]
  23. Yavari, I.; Hekmat-Shoar, R.; Zonousi, A. Anewand efficient route to 4-carboxymethylcoumarins mediated by vinyltriphenylphosphonium salt. Tetrahedron Lett. 1998, 39, 2391–2392. [Google Scholar] [CrossRef]
  24. Pechmann, H.V.; Duisberg, C. Uber die verbindungen der phenole mit acetessigather. Ber. Dtsch. Chem. Ges. 1883, 16, 2119–2128. [Google Scholar] [CrossRef]
  25. Surasani, R.; Kalita, D.; Dhanunjaya Rao, A.V.; Yarbagi, K.; Chandrasekhar, K.B. FeF3 as a novel catalyst for the synthesis of polyhydroquinoline derivatives via unsymmetrical Hantzsch reaction. J. Fluorine Chem. 2012, 135, 91–96. [Google Scholar] [CrossRef]
  26. Atar, A.B.; Jeong, Y.S.; Jeong, Y.T. Iron fluoride: The most efficient catalyst for one-pot synthesis of 4H-pyrimido[2,1-b]benzothiazoles under solvent-free conditions. Tetrahedron 2014, 70, 5207–5213. [Google Scholar] [CrossRef]
  27. Sabetpoor, S.; Hatamjafari, F. Synthesis of coumarin derivatives using glutamic acid under solvent-free conditions. Orient. J. Chem. 2014, in press. [Google Scholar]
  28. Hatamjafari, F.; vahabi, V. A novel synthesis of biscoumarin derivatives catalyzed by ZnCl2 under solvent-free conditions. Orient. J. Chem. 2013, 29, 783–786. [Google Scholar] [CrossRef]
  29. Hatamjafari, F.; Montazeri, N. Three-component process for the synthesis of some pyrrole derivatives under microwave irradiation. Turk. J. Chem. 2009, 33, 797–802. [Google Scholar]
  30. Azizian, J.; Hatamjafari, F.; Karimi, A.R.; Shaabanzadeh, M. Multi-component reaction of amines, alkyl propiolates, and ninhydrin: An efficient protocol for the synthesis of tetrahydro-dihydroxy-oxoindeno[1,2-b]pyrrole derivatives. Synthesis 2006, 5, 765–767. [Google Scholar]
  31. Azizian, J.; Shaabanzadeh, M.; Hatamjafari, F.; Mohammadizadeh, M.R. One-pot rapid and efficient synthesis of new spiro derivatives of 11H-indeno[1,2-b]quinoxalin-11-one, 6H-indeno[1,2-b]pyrido[3,2-e]pyrazin-6-one and isatin-based 2-pyrazolines. ARKIVOC 2006, 2006, 47–58. [Google Scholar]
  32. Hatamjafari, F. New protocol to synthesize spiro-1,4-dihydropyridines by using a multicomponent reaction of cyclohexanone, ethyl cyanoacetate, isatin, and primary amines under microwave irradiation. Synth. Commun. 2006, 36, 3563–3570. [Google Scholar] [CrossRef]
  33. Azizian, J.; Hatamjafari, F.; Karimi, A.R. Four component and solvent-free synthesis of some new spiro-1,4-dihydropyridines on solid support montmorillonite K10. J. Heterocycl. Chem. 2006, 43, 1349–1352. [Google Scholar] [CrossRef]
  34. Hatamjafari, F. A green, reusable and highly efficient heterogeneous catalyst for the synthesis of arylpyrazoles using nano-Fe2O3. Orient. J. Chem. 2012, 28, 141–143. [Google Scholar] [CrossRef]
  35. Hatamjafari, F. Microwave assisted synthesis of arylpyrazoles using montmorillonite K-10. Asian J. Chem. 2012, 25, 2339–2340. [Google Scholar]
  36. Hatamjafari, F. Starch-sulfuric acid (SSA) as catalyst for a one-pot synthesis of 1,5-diaryl-1H-pyrazoles. Helv. Chim. Acta 2013, 96, 1560–1563. [Google Scholar] [CrossRef]
  37. Banothu, J.; Bavantula, R. (4-Sulfobutyl)tris(4-sulfophenyl)phosphonium hydrogen sulphate: An efficient, eco-friendly and recyclable catalyst for the synthesis of coumarin derivatives via Pechmann condensation under solvent-free condition. Adv. Appl. Sci. Res. 2013, 4, 74–78. [Google Scholar]
  38. Karami, B.; Kiani, M. A one-pot, three-component synthesis of new pyrano[2,3-h]coumarin derivatives. Catal. Commun. 2011, 14, 62–67. [Google Scholar] [CrossRef]
  39. Vahdat, S.M. An green and efficient one-pot synthesis of coumarin derivatives catalyzed by cerium(IV) triflate at room temperature. J. Appl. Chem. 2012, 7, 57–62. [Google Scholar]
  40. Devi, P.U.M.; Reddy, S.P.; Rani, N.R.U.; Reddy, K.J.; Reddy, M.N.; Reddanna, P. Lipoxygenase metabolites of α-linolenic acid in the development of resistance in pigeonpea, Cajanus cajan (L.) Millsp., seedlings against Fusarium udum infection. Eur. J. Plant Pathol. 2000, 106, 857–865. [Google Scholar] [CrossRef]
  41. Colle, J.G.; Duguid, J.P.; Firaser, A.G.; Mannion, B.P. Mackie & Mecartney Practical MedicinalMicrobiology,, 13th ed.; Churchill: Edinburgh/London, UK, 1989; pp. 553–558. [Google Scholar]
  • Sample Availability: Samples of the compounds 15, 12 and 13 are available from the authors.
Back to TopTop