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3-Acetyl-4-hydroxycoumarin: Synthesis, reactions and applications
⁎Tel.: +20 1000409279. moaz.chem@gmail.com (Moaz M. Abdou)
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This article was originally published by Elsevier and was migrated to Scientific Scholar after the change of Publisher.
Peer review under responsibility of King Saud University.
Abstract
The chemistry of 3-acetyl-4-hydroxycoumarin has gained increased interest in both synthetic organic and biological fields, since a large number of developments in the use of such compound seem to be of considerable value. This review summarizes results from the literature concerning the synthesis and reactions of 3-acetyl-4-hydroxycoumarin as well as its applications are also discussed.
Keywords
3-Acetyl-4-hydroxycoumarin
Synthesis
Chemical reactivity
Condensation
Cyclization
Heterocycles
1 Introduction
3-Acetyl-4-hydroxycoumarin represents the core structure of several natural products and is the central pharmacophore found in a number of medicinal agents such as antimicrobial, antifungal and antioxidant agents (Mladenovic et al., 2009; Al-Ayed, 2011). These special properties turn 3-acetyl-4-hydroxycoumarin into very interesting targets to organic chemists, and several strategies for their synthesis were developed including acylation, bromination, metalation, and Claisen–Schmidt condensation.
In spite of these interesting advances, there is no review of the utility of 3-acetyl-4-hydroxycoumarin in organic synthesis, it is hoped that this survey will provide a useful guide of the synthetic approaches for the preparation of 3-acetyl-4-hydroxycoumarin as well as the progress that has been made in organic synthesis using them as starting materials. The presentation will begin with the methods of synthesis of 3-acetyl-4-hydroxycoumarin and the reactivity of it will follow. Finally, some of the applications of 3-acetyl-4-hydroxycoumarin will be presented. I hoped that this review will demonstrate the synthetic potential of 3-acetyl-4-hydroxycoumarin and generate some new ideas in this area.
2 Molecular structures and spectral properties
The structure of 3-acetyl-4-hydroxycoumarin has been assigned by UV (Klutchko et al., 1974; Traven et al., 1997), IR (Naceur et al., 2011; Eiden and Rademacher, 1983; Babin et al., 1981), MS (Naceur et al., 2010; Fischmeister et al., 2011; Sukdolak et al., 2004), NMR (Li et al., 2012a; Athanasellis et al., 2004; Kravchenko et al., 1999), fluorescence (Li et al., 2012a) and photoelectron (Traven et al., 2000) spectroscopy. The UV–Vis absorption and photoluminescence spectra of 3-acetyl-4-hydroxycoumarin in dilute dichloromethane solutions revealed a sharp absorption peak at 300 nm, with a shoulder at 341 nm (Li et al., 2012a). The analysis of IR spectrum of it, showed bands resulting from the OH, (ketone) C⚌O and (lactone) C⚌O stretching in the region 3185, 1705 and 1700 cm−1, respectively (Palinko et al., 1995).
The proton NMR spectrum of 3-acetyl-4-hydroxycoumarin (Al-Ayed, 2011) revealed the aromatic protons as a multiplet between 7.24 and 8.01 ppm. A singlet at 2.74 ppm was assigned to the methyl protons while the OH signal appeared at 17.72 ppm. This very high value of the chemical shift might be explained by only an intermolecular hydrogen bond (David and Michael, 2001; Hamdi et al., 1993; Traven et al., 2005).
The 13C NMR spectrum of 3-acetyl-4-hydroxycoumarin in “DMSO-d6” (Sukdolak et al., 2004) revealed two downfield signals at δ 162.42 (ketone “C⚌O”) and δ 157.41 (lactone “C⚌O”). Measurement of the spectrum using the DEPT technique showed that the four aromatic carbons of the coumarinic ring appear at δ 134.5, 131.3, 125.6 and 124.11.
HeI photoelectron spectrum of 3-acetyl-4-hydroxycoumarin is shown in Fig. 1 (Traven et al., 2005). It represents an enol form of the coumarin derivative. Moreover, in order to establish unambiguously the structure, the identification of this compound was carried out by X-ray structure determination (Naceur et al., 2011). The structure of this compound exhibits also intramolecular hydrogen bond of the type O–H–O. The intramolecular hydrogen bond between the hydroxyl group and the ketonic oxygen is O3A–H8A–O2A having a length of 1.412 Å (vide Fig. 2).
HeI photoelectron spectrum of 3-acethyl-4-hydroxycoumarin (Traven et al., 2005).
ORTEP diagram of compound 1 at 50% probability (Naceur et al., 2011).
3 Tautomeric structure (S)
3-Acetyl-4-hydroxycoumarin can exist in four tautomeric keto-enol forms (Fig. 3). These possible prototropic transformations have been investigated experimentally by UV spectroscopy and theoretically by the semi-empirical and non-empirical quantum chemical calculations (Traven et al., 1997, 2000; Stanovnik et al., 2006; Lyssenko and Antipin, 2013). According to these studies, 3-acetyl-4-hydroxycoumarin mainly exists in endocyclic enol form (B) in solid states. In addition the major tautomer of this compound present in solution is highly dependent on solvent polarity, that is, the tautomer (A) was found to be predominant in non-polar solvents (n-hexane, CCl4), whereas in polar solvents (methanol, ethanol) the dioxo tautomer (B) was favored. Also, calculations at all levels predict (A) and (B) to be more stable than the other possible tautomers (C) and (D) and almost isoenergetic, the energy difference being only about 1 kcal/mol.
Possible tautomeric structures of 3-acetyl-4-hydroxycoumarin (A–D).
4 Chemical reactivity
It is evident from the topography of 3-acetyl-4-hydroxycoumarin that it possesses both electrophilic and nucleophilic properties. The reactivity of 3-acetyl-4-hydroxycoumarin is based on their keto-enol tautomerism. (Fig. 3). The most significant reactivity is the nucleophilicity and electrophilicity of acetyl group at the position 3. These factors make the third position in the coumarin ring very convenient for many reactions and a good precursor for preparing fused ring systems through cyclization procedure A and B (Fig. 4).
Possible precursor for preparing fused ring systems through cyclization procedure A and B.
5 Methods of the synthesis
Many synthetic approaches to 3-acetyl-4-hydroxycoumarin 1 have been reported, mainly using 4-hydroxycoumarin or phenol as starting material.
5.1 Using 4-hydroxycoumarin
The direct acetylation of 4-hydroxycoumarin 2 with acetyl chloride 3 using pyridine or piperidine as a catalyst gave 3-acetyl-4-hydroxycoumarin 1 (Stadlbauer and Hojas, 2004; Klosa, 1956) (Scheme 1).
Moreover, several reports on synthetic routes for 3-acetyl-4-hydroxycoumarin 1 have been published during the last decade via the reaction of 2 with acetic acid or acetic anhydride 4 in the presence of phosphorous oxychloride as a catalyst (Sukdolak et al., 2004; Li et al., 2012a; Traven et al., 2000; Lyssenko and Antipin, 2013; Mulwad and Hegde, 2009; Hamdi et al., 2008; Eisenhauer and Link, 1953; Klosa, 1955; Ukita et al., 1950; Dholakia et al., 1968) (Scheme 2).
O-acylation of 4-hydroxycoumarin 2 with acetyl chloride 3 in the presence of triethylamine in methylene chloride gave the corresponding enol esters 5, which were further treated with trichlorophosphate in acetic acid (Kravchenko et al., 1999) or potassium cyanide with triethylamine in dichloromethane (Liao et al., 2003) yielding 3-acetyl-4-hydroxycoumarin 1 (Scheme 3).
5.2 Hydrolysis and deacetylation of 4-acetoxy-3-acetyl coumarin
Al-Sehemi and El-Gogary (2012) disclosed a simple and inexpensive synthesis of 1 in 73% yield via the acid-catalyzed deacylation of 4-acetoxy-3-acetyl coumarin 6 (Scheme 4).
5.3 Hydrolysis of 3-acetyl-4-difluoro boryloxycoumarin
Hydrolysis of 3-acetyl-4-difluoro boryloxycoumarin 7 in an aqueous alcoholic solution of sodium carbonate afforded 1 (Manaev et al., 2006) (Scheme 5).
5.4 Using phenol
Heating phenol 8 with 2-acetyl malonic acid 9 in phosphorus oxychloride containing twofold amount of anhydrous zinc chloride furnished 1 (Shah et al., 1960) (Scheme 6).
6 Chemical Reactions
6.1 Acetylation reaction
Acetylation of 1 with acetyl chloride under basic conditions occurs specifically at 3-enolic oxygen to give the enol ester 6. The electrostatic repulsion between the 3-acyl oxygen atom and the two 1,3-diketone oxygens of the resulting enol ester caused deformation of the triketone functional group from planarity. This repulsion can be easily relieved via enolization of the 3-acyl group of 6, followed by a 1,5-acyl transfer reaction to afford enol acetate 10. The resulting 11 can then undergo esterification again to obtain enol diacetate 11 (Chen et al., 2006) (Scheme 7).
6.2 Bromination reaction
Bromination of 3-acetyl-4-hydroxycoumarin 1 with phenyltrimethylammonium tribromide 12 in tetrahydrofuran afforded a high yield of 3-(2-bromoacetyl)-4-hydroxycoumarin 13. This bromination method is more convenient than the existing procedures in terms of safety for large-scale application, ease in controlling the reaction and no evolution of hazardous gas (Sukdolak et al., 2004) (Scheme 8).
When bromination of 1 is carried out using a conventional manner (bromine/acetic acid), it afforded substitution product at the aromatic nucleus as a major product 14 (Li et al., 1987; Takase et al., 1971; Grakauskas, 1970; Friederang et al., 1969) (Scheme 9).
6.3 Reduction reaction
Kappe and coworkers have reported that a simple and effective method for the reduction of 1 to 3-ethyl-4-hydroxycoumarin 15 was achieved by using zinc powder in acetic acid/hydrochloric acid as the reducing agent (Kappe et al., 1995) (Scheme 10).
6.4 Deacetylation reaction
Jung et al. have recently demonstrated that treatment of 3-acetyl-4-hydroxycoumarin 1 with concentrated sulfuric acid afforded 4-hydroxycoumarin 16 in 90.2% yield (Jung et al., 1999) (Scheme 11).
6.5 Methylation reaction
3-Acetyl-4-methoxycoumarin 17 was obtained via methylation reaction of 1 with diazomethane at room temperature in the presence of a catalytic amount of triethylamine (Jung et al., 1999) (Scheme 12).
6.6 Metalation reaction
Heating 3-acetyl-4-hydroxycoumarin 1 in a mixture of boron trifluorideetherate in dry toluene (Naceur et al., 2010) or benzene (Traven et al., 2005; Manaev et al., 2006) gave rise to the 3-acetyl-4-difluoro boryloxycoumarin 18 with good yield (Scheme 13).
3-Acetyl-4-(1,3,2-benzodioxaborol-2-yloxy)coumarin 20 was synthesized by refluxing of 3-acetyl-4-hydroxycoumarin 1 and 2-hydroxy-1,3,2-benzodioxaborole 19 in dry benzene (Manaev et al., 2006) (Scheme 14).
6.7 Condensation with aldehydes
A series of coumarinic chalcones 22 were synthesized by Claisen–Schmidt condensation of 1 with various aryl or heteroaryl aldehydes 21 in the presence of piperidine in chloroform (Al-Ayed, 2011; Naceur et al., 2011; Patel et al., 2011), benzene (Lin et al., 2005), ethanol (Abdelhafez et al., 2010; Matos et al., 2013) or acetic acid (Li et al., 2012a,b) (Scheme 15). The presence of coumarin nucleus gives to these species an important pharmacological and therapeutic interest. Antioxidant activities of these compounds against the stable free radical DPPH showed that these species are a good source of compounds that could help to increase the overall antioxidant capacity of an organism. Also, these compounds exhibit high fluorescence quantum yields, large Stokes shifts, and strong blue emissions.
Siddiquiet al. have described an efficient and eco-friendly methodology for the above condensation via employing Zn(l-proline)2 as a recyclable Lewis acid catalyst in water. In each conversion, the catalyst was successfully recovered and reused several times without significant loss in yield and selectivity (Siddiqui et al., 2008, 2011; Siddiqui and Mohammed, 2011).
6.8 Knoevenagel condensation
The solvent-free conditions for the fast synthesis of novel coumarin derivatives by the Knoevenagel condensation under microwave irradiation were reported by Mladenovic and coworkers. Different carbonyl, ester and cyano derivatives 23 were used in the condensations with 1 to achieve structural variety in the produced coumarins 24 (Mladenovic et al., 2009) (Scheme 16).
6.9 Reaction with active methylene
A series of 3-acetyl-4-hydroxycoumarins incorporating pyridine nucleus linked at C-3 have been prepared as potential anticoagulant agents. 4-Aryl-2-amino-6-(3-acetyl-4-hydroxycoumarin-3-yl)-pyridin-3-carbonitriles 25 were prepared by direct one pot reaction of 1 with the appropriate aldehydes in the presence of malononitrile and ammonium acetate (Abdelhafez et al., 2010) (Scheme 17).
On the other hand, when the above reactions were carried out in the presence of ethylcyanoacetate instead of malononitrile, 4-aryl-1,2-dihydro-6-(3-acetyl-4-hydroxycoumarin-3-yl)-2-pyridin-3-carbonitriles 26 were obtained (Abdelhafez et al., 2010) (Scheme 18).
6.10 Synthesis of imines and enaminones
The broad range of applications of imino derivatives of 3-acetyl-4-hydroxycoumarins 28 has led to the development of its synthetic method. Recently several workers have reported the synthesis of 28 via the condensation reaction of 1 with various amines 27 either under conventional heating (Bavishi et al., 2013; Jevtic et al., 2013) or under microwave irradiation (Mladenovic et al., 2009; Vukovic et al., 2010a,b) (Scheme 19). It is worth to note that the yield has been significantly increased using reaction under microwave irradiation particularly in case of imino derivatives with p-nitrophenyl (92%), m-nitrophenyl (97%) and pentanoic acid substituent (87%).
In a similar manner, the reaction of 3-acetyl-4-hydroxycoumarin 1 with an excess of N,N-dimethyl formamide dimethyl acetal (DMF-DMA) 29 Hamdi et al., 2008; Siddiqui and Farooq, 2012; Ahmed and Siddiqui, 2013 afforded the corresponding 3-(3-(dimethylaminoacryloyl)-3-acetyl-4-hydroxycoumarin 30 (Scheme 20).
6.11 Reaction with hydroxylamine
Review of the literature reveals some confusion and uncertainty about the assignment of the structure of the reaction products of 1 with hydroxylamine. In 1955, Klosa (Klosa, 1955) reported that 1 gave crystalline oxime 31 on treatment with an excess of hydroxylamine hydrochloride and potassium acetate in refluxing ethanol. After that, Desai and Usgaonkar (Desai et al., 1977) have suggested that the “oximes” of Klosa were the 4H[l]benzopyrano[3,4-d]isoxazol-4-one 32. They found that the oxime of 31 can be obtained only at room temperature and reported that they did not undergo Beckmann rearrangement but readily cyclodehydrated to 32. The formation of the isoxazole 32 from 3-acetyl-4-hydroxycoumarin 1 under basic conditions at room temperature was also reported by Makkay and Makkay (1979).
In 1984, Chantegrel et al. (1984) repeated Klosa’s work found that the reaction of 1 with hydroxylamine under basic condition, afforded a mixture of 4-(2-hydroxybenzoyl)-3-methylisoxazol-5(4H)-one 33 as the main product accompanied by 4-methyl-3H-[l]-benzopyrano[4,3-c]isoxazol-3-one 34 (Scheme 21). Recently, Latypov and coworkers Latypov et al. (2008) found that this reaction under reflux in acetic acid afforded 2-methyl-4H-chromeno[3,4-d][1,3]oxazol-4-one 35 (Scheme 21).
6.12 Synthesis of hydrazones
The condensation reaction of arylhydrazine hydrochlorides or arylhydrazines 36 with 1 either in refluxing acetic acid (Stadlbauer and Hojas, 2004) or ethanol (Catarzi et al., 1995; Colotta et al., 1988) furnished the corresponding hydrazones 37 (Scheme 22).
On the contrary, it has been reported that the same reaction led to fission of the coumarin ring giving the corresponding 2-(substituted)-4-(2-hydroxybenzoyl)-1H-pyrazol-3-ol 38 (Chantegrel et al., 1983; Budzisz et al., 2007) (Scheme 23).
6.13 Reaction with acid hydrazide
3-Acetyl-4-hydroxycoumarin-N-acylhydrazones 40 were synthesized via treatment of 3-acetyl-4-hydroxycoumarin 1 with the appropriate hydrazide 39 in propanol (Kotali et al., 2012), or methanol (Somogyi and Sohar, 1995) as depicted in Scheme 24. The molar ratio of the reactants was 1/1 and the reaction was performed under reflux either for 24 h to yield hydrazones 40 in very good yields (70–98%) or for 2 h to lead to the formation of hydrazones 40 in slightly lower yield (60–81%) (Scheme 24).
6.14 Synthesis of fused ring systems
6.14.1 Pyranochromenones
Maigali et al. (2011) have exploited a very simple and efficient method for the synthesis of pyranochromones 43. The reaction of the active phosphoranes 41 with 1 in boiling toluene afforded the corresponding 4-methyl-2-(phenylimino)pyrano[3,2-c]chromen-5(2H)-one 43a or 4-methyl-2H,5H-pyrano-[3,2-c]chromene-2,5-dione 43b, respectively, together with triphenylphosphine oxide 44. Compounds 43a and 43b were formed via the formation of the complex phosphoranes 44, followed by intramolecular Wittig reaction affording 43a and 43b (Scheme 25).
6.14.2 Oxaphosphino-chromenones
Maigali and coworkers showed that 4-methyl-2,2,2-triphenyl-2H,5H-2λ5-[1,2]oxaphosphinino[5,6-c]chromen-5-one 47 was prepared via the reaction of hexaphenylcarbodiphosphorane 45 through intramolecular cyclization of the intermediate 46 (Maigali et al., 2011) (Scheme 26).
6.14.3 Pyrazols
The condensation of different hydrazines 48 with 1 in ethanol (Mustafa et al., 1965) or under the influence of microwave irradiation and Zn[l-proline]2 as a novel reusable Lewis acid catalyst (Manvar et al., 2007) furnished 3-methyl-1H-chromeno[4,3c]pyrazol-4-one 49 (Scheme 27).
However, refluxing of 3-acetyl-4-hydroxycoumarin 1 with 2-hydrazinopyridine 50 in a 1:1 M ratio in methanol gave 4-(2-hydroxybenzoyl)-2-(pyridin-2-yl)-1H-pyrazol-3-ol 51 in 62% yield (Budzisz et al., 2007) (Scheme 28).
6.14.4 Dihydrobenzopyran-bis benzopyranopyran-6,14-dione
An elegant, efficient one-pot synthesis of 7-[3-acetyl-2-oxo-3,4-dihydro-2H-[1]benzopyran-4-yl]methyl-6H,14H-bis[1]benzopyrano)[4,3-b:4′,3′-d]pyran-6,14-dione 52 was accomplished by treatment of 4-hydroxycoumarin 16 with 1 in a glacial acetic acid in the presence of potassium acetate (Manolov et al., 2006) (Scheme 29).
6.14.5 Dioxabicyclo[3.3.1]nonane
The base catalyzed condensation reaction between 4-hydroxycoumarin 16 and 1 in water under reflux led to the formation of 1-methyl(1-phenyl)-benzopyrano[4′,3′-c]-benzo[3″,4″-f]-2,8-dioxabicyclo[3.3.1]nonane 53 via Michael addition (Manolov et al., 2006) (Scheme 30).
7 Applications
3-Acetyl-4-hydroxycoumarin is important as product and intermediate in analytical, biological and pharmaceutical chemistry.
7.1 Analytical uses
3-Acetyl-4-hydroxycoumarin is useful for the extraction and separation of uranium from thorium, and the determination of these elements, even in the presence of more than ten times the amount of ceriumlll and lanthanum, can be readily accomplished by using 3-acetyl-4-hydroxycoumarin as a complexing agent, because of the marked differences in the solubilities in ethanol of the complexes (Bhat and Jain, 1960).
7.2 Biological uses
3-Acetyl-4-hydroxycoumarin was capable of inhibiting the growth of strains of bacteria (Staphylococcus aureus (ATCC 25925), S. aureus (clinical isolate, IHP), Escherichia coli (ATCC 25922), Micrococcus lysodeikticus (ATCC 4698), Bacillus subtilis (clinical isolate, IHP), and Klebsiella pneumoniae (clinical isolate, IHP)) and one strain of fungi (Candida Albicans (ATCC 10259)) Mladenovic et al., 2009.
7.3 Miscellaneous uses
The oxidation potentials as well as the diphenylpicrylhydrazyl (DPPH) radical scavenging activity for 3-acetyl-4-hydroxycoumarin have been detected and compared with Trolox. 3-Acetyl-4-hydroxycoumarin was found to be more effective in a DPPH radical scavenging assay than trolox, with an Inhibitory concentration (IC50) value of 2.35 mM as compared to trolox with IC50 value of 2.30 Mm (Al-Ayed, 2011).
8 Conclusion
The literature survey presented herein indicates that the synthesis, tautomerism and chemical reactivity of 3-acetyl-4-hydroxycoumarin as well as its reactions have attracted the interest of many research groups all over the world. Apart from the synthetic interest, the known and expected analytical, biological application of the title compounds deserves a particular mention. Finally, I hope that this review serves as a stimulus for ongoing research in the area of 3-acetyl-4-hydroxycoumarin chemistry.
Acknowledgements
I am very indebted to my capable and enthusiastic members and co-workers whose names appear in the list of references. The Academy of Scientific Research and Technology, ASRT, Egypt is acknowledged for their continuous financial support.
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