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Montmorillonite Clay Catalysis. Part 7.1An Environmentally Friendly Procedure for the Synthesis of CoumarinsviaPechmann Condensation of Phenols with Ethyl Acetoacetate†

 

作者: Tong-Shuang Li,  

 

期刊: Journal of Chemical Research, Synopses  (RSC Available online 1998)
卷期: Volume 0, issue 1  

页码: 38-39

 

ISSN:0308-2342

 

年代: 1998

 

DOI:10.1039/a703694i

 

出版商: RSC

 

数据来源: RSC

 

摘要:

R OH + O CO2Et R O O Me K-10 or KSF toluene, reflux 0-96 % 1 2 38 J. CHEM. RESEARCH (S), 1998 J. Chem. Research (S), 1998, 38–39† Montmorillonite Clay Catalysis. Part 7.1 An Environmentally Friendly Procedure for the Synthesis of Coumarins via Pechmann Condensation of Phenols with Ethyl Acetoacetate† Tong-Shuang Li,* Zhan-Hui Zhang, Feng Yang and Cheng-Guang Fu Department of Chemistry, Hebei University, Baoding 071102, Hebei Province, P.R. China Coumarins are synthesised via Pechmann condensation of phenols with ethyl acetoacetate catalysed by montmorillonite clay in satisfactory yields; the scope and limitation of the method have been investigated.Coumarins occupy a special place in the realm of natural and synthetic organic chemistry because many products which contain this subunit exhibit useful and diverse biological activity such as molluscacides,2 have anthelmintic, hypnotic and insecticidal properties,3 or serve as anticoagulant agents4 or fluorescent brighteners.5 These compounds can also be used for the synthesis of other products such as furocoumarins, chromenes, coumarones and 2-acylresorcinols.6 There have been many synthetic routes to the coumarins7 including the Pechmann,8 Perkin,9 Knoevenagel,10,11 Reformatsky12 and Wittig5,13 reactions.However, the Pechmann reaction has been the most widely applied method for preparing coumarins since it proceeds from very simple starting materials and gives good yields of coumarins substituted in either the pyrone or benzene ring or in both.The course of the reaction depends on the substituents on the phenol, on the catalyst used and on the nature of the b-oxo ester. The Pechmann reaction has been studied with homogeneous acid catalysts such as sulfuric, hydrochloric, phosphoric8 and tri- fluoroacetic acid,14 and with Lewis acids such as zinc chloride, iron(III) chloride, tin(IV) chloride, titanium chloride and aluminium chloride.8 However, these conventional catalysts have to be used in excess, and they are subject to increasing environmental pollution and are non-recoverable.Consequently, there is a need for efficient and heterogeneous catalytic methods for this reaction by using inexpensive, easily handled and non-polluting catalysts. Cation-exchange resins,15 Nafion-H,16 zeolite-HBEA and other solid acids17 have been employed for this purpose. More recently, microwave irradiation was applied to accelerate this reaction.18 Montmorillonite clays have been used as efficient catalysts for a variety of organic reactions.19 They are inexpensive nontoxic powders which can be filtered easily from reaction mixtures and may be reused.However, syntheses of coumarins directly catalysed by montmorillonite clays have not been reported. In connection with our work on montmorillonite clays catalysis,20 herein we describe an environmentally friendly procedure for the synthesis of coumarins via Pechmann reaction catalysed by montmorillonite K-10 and KSF.As shown in Table 1, in the presence of montmorillonite clays, several phenols (1a, 1b 1f) and ethyl acetoacetate were *To receive any correspondence (e-mail: orgsyn@hbu.edu.cn). †This is a Short Paper as defined in the Instructions for Authors, Section 5.0 [see J. Chem. Research (S), 1998, Issue 1]; there is therefore no corresponding material in J. Chem. Research (M). Scheme 1 Table 1 Synthesis of coumarin from phenols with ethyl acetoacetate catalysed by montmorillonite clays Yield(%)a Mp (T/°C) Coumarin Catalyst/solvent/ Phenol substituents temp.(T/°) t/h Found Lit. Found Reported Resorcinol (1a) 4-Me-7-OH K-10/none/150 4 96 9016 188–188.5 18416 K-10/toluene/reflux 8 94 KSF/none/150 5 88 KSF/toluene/reflux 10 90 Phloroglucinol (1b) 4-Me-5,7-(OH)2 K-10/toluene/reflux 8 85 49.115 284–285 284.5–28515 KSF/toluene/reflux 8 88 Pyrogallol (1c) 4-Methyl-7,8-(OH)2 K-10/toluene/reflux 10 66 5616 234–235 23316 m-Cresol (1d) 4,7-Me2 K-10/none/150 8 69b 2516 131.5–132 13416 KSF/none/150 12 61b p-Cresol (1e) 4,6-Me2 K-10/none/150 12 61b 014 149–150 150–15124 a-Naphthol (1f) 4-Me-7,8-benzo K-10/none/150 8 80 8521 170.5–171 17021 Phenol (1g) 4-Me K-10/none/150 10 65b 322 83–84 83–8423 2-Naphthol (1h) 4-Me-6,7-benzo K-10/none/150 12 68b 2025 182–183 18325 2-Nitrophenol (1i) no reaction K-10/none-150 12 —c 3-Nitrophenol (1j) no reaction K-10/none/150 12 —c 4-Nitrophenol (1k) no reaction K-10/none/150 12 —c 2-Chlorophenol (1l) no reaction K-10/none/150 12 —c 2,4-Dichlorophenol (1m) no reaction K-10/none/150 12 —c Hydroquinone (1n) no reaction K-10/none/150 12 —c Salicylaldehyde (1o) no reaction K-10/none/150 12 —c 4-Hydroxybenzaldehyde (1p) no reaction K-10/toluene/reflux 12 —c 2-Aminophenol (1q) no reaction K-10/toluene/reflux 12 —c 4-Aminophenol (1r) no reaction K-10/toluene/reflux 12 —c 4-(4-Nitrophenylazo)orcinol (1s) no reaction K-10/toluene/reflux 12 —c aIsolated yield.bNet yield, conversion rate of 1d=15%, conversion rate of 1e=4%, conversion rate of 1g=7%, conversion rate of 1h=5%. c100% of starting materials were recovered.J. CHEM. RESEARCH (S), 1998 39 heated in the absence of solvent or in refluxing toluene to give the corresponding coumarins in high yields. Pyrogallol (1c) afforded a good yield, m-cresol (1d), p-cresol (1e), phenol (1g) and b-naphthol (1h) provided poor conversion rates whereas nitrophenol (1i, 1j and 1k), 2-chlorophenol (1l), 2,4-dichlorophenol (1m), hydroquinone (1n), salicylaldehyde (1o), p-hydroxybenzaldehyde (1p), o-aminophenol (1q), p-aminophenol (1r) and 4-(p-nitrophenylazo)orcinol (1s) all failed to afford the corresponding coumarins.From the experimental results, it can be proved that phenols having electron-donating substituents in the position meta to the phenol hydroxy group promote the condensation. The +E effects of these substituents support formation of the reactive polarised carbonation in the ortho position. An alkyl group is not strong enough to furnish the activation needed and thus gives a low yield (1d).In contrast, electron-withdrawing groups inhibit the reaction. Generally speaking, K-10 worked better than KSF in term of reaction time and yield. The optimum amount of the catalyst used was between 25 and 30% by weight of the total reactants. Catalysts were easily regenerated by washing with ethanol, followed by drying at 110 °C for 12 h.The catalyst K-10 and KSF could be reused four times in the reaction with 1a without significant loss of activity. In conclusion, the use of montmorillonite clays as heterogeneous catalysts is a viable alternative to existing procedures. Furthermore, this method is advantageous because of easy separation, consistent yield, minimal environmental effects and recyclability of the catalyst. Experimental Melting points are uncorrected. Montmorillonite K-10 and KSF were purchased from Fluka and dried at 100 °C prior to use.Ethyl acetoaceate and all liquid phenols were distilled before use. The products were characterized by their melting points and/or IR and 1H NMR spectra and by comparison with their literature data. General Procedure for the Synthesis of Coumarins.—A mixture of the phenolic compound 1 (5 mmol), ethyl acetoaceate (5 mmol) and montmorillonite K-10 (or KSF) (30 wt% to 1 and ethyl acetoacetate) was refluxed in toluene (10 ml) using a Dean– Stark apparatus to remove water (or heated at 150 °C for those reactions in the absence of solvent) with constant stirring for 4–12 h as indicated in Table 1.The reaction was monitored by TLC. The montmorillonite was filtered off and washed with hot ethanol (2Å5 ml). The solvent was removed under reduced pressure to afford the crude product. The crude product was purified by column chromatography on silica gel [light peroleum (bp 60–90 °C)–ethyl acetate as eluent] to give the pure coumarin 2, yield 0–96% (Table 1).We are grateful to NSFC (29572039), the Science and Technology Commission of Hebei Province and the Education Commission of Hebei Province for financial support. Received, 28th May 1997; Accepted, 29th September 1997 Paper E/7/03694I References 1 Part 6, Z.-H. Zhang, F. Yang, T.-S. Li and C.-G. Fu, Synth. Commun., 1997, 27, 3823. 2 A. Schonberg and N. Latif, J. Am. Chem. Soc., 1954, 76, 6208. 3 A. Mitra, S. K. Misra and A. Patra, Synth. Commun., 1980, 10, 915. 4 L. A. Singer and N. P. Kong, J. Am. Chem. Soc., 1966, 88, 5213. 5 N. S. Narasimhan, R. S. Mali and M. V. Barve, Synthesis, 1979, 906. 6 S. M. Sethna and N. M. Shah, Chem. Rev., 1945, 36, 1. 7 S. Wawzoek, in Heterocyclic Compounds, ed. R. C. Elderfield, Wiley, New York, 1951, vol. 2, p. 173. 8 S. Sethna and R. Phadka, Org. React., 1953, 7, 1. 9 J. R. Johnson, Org. React., 1942, 1, 210. 10 G. Jones, Org. React., 1967, 15, 204. 11 G. Brufola, F. Fringuelli, O. Piermatti and F. Pizzo, Heterocycles, 1996, 43, 1257. 12 R. L. Shirner, Org. React., 1942, 1, 1. 13 R. S. Mali, S. N. Yeola and B. K. Kulkarni, Indian J. Chem., 1983, 22B, 352. 14 L. L. Woods and J. Sapp, J. Org. 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