Synthesis of Coumarins via Pechmann Reaction

Dong, F., Jain, C., Kai, G., Qunrong, S., Zuliang, L. 2008. Synthesis of coumarins via Pechmann reaction in water catalysed by acyclic acidic ionic liquids. Catal. Lett. 121 255-259. 

In comparison, 40 is much more acidic than zeolites and metal-substituted mesoporous acidic catalysts. The KIT-5-(100)-20TA demonstrates an advanced and higher activity and superiority of performance in the synthesis of coumarins via Pechmann reaction (10MI2843). 

N.G. Khaligh, Synthesis of coumarins via Pechmann reaction catalyzed by 3-methyl-l-sulfonic acid imidazoUum hydrogen sulffite as an efficient, halogen-free and reusable acidic ionic liquid, Catal. Sci. Technol. 2 (2012) 1633-1636. 

Potdar et al. (2005) employed neutral ILs such as [bmimjPFa or [bmim]BF4 with catalytic amount of acid for synthesis of coumarin via Pechmann condensation of phenols and ethyl acetoacetate (EAA) under ambient conditions. They also carried out the reaction at high temperature in IL [bmimJPFe, without the use of any acid catalyst and investigated the recycling of the ILs for reuse. 

Sinhamahapatra et al. (2011) reported that the microwave-assisted synthesis is the most appropriate method for synthesis of coumarins as it provides improved yield in very less time. Mesoporous zirconium phosphate (m-ZrP) is used as a solid acid catalyst for the synthesis of coumarins via Pechmann condensation reaction. Among the substituted phenols, m-amino phenol is more reactive and 100% yield was obtained in very short time at low temperature due to the presence of ring activating amine group in meta position. The m-ZrP is also active towards phenols for the synthesis of 4-methyl coumarin, where only 57% yield was obtained in conventional heating method. 

Zeolites have been shown to catalyse a variety of related reactions (Downing et al., 1997), e.g. zeolite beta catalyses the synthesis of coumarins via the Pechmann condensation. For example, condensation of resorcinol with ethyl acetoacetate over zeolite beta in refluxing toluene gave methylumbelliferone, a perfumery ingredient, in 70-80% yield (Fig. 2.24) (Gunnewegh ef a/., 1996). 

The classical Pechmann approach for the synthesis of coumarins via the micro-wave-promoted reaction [68] has been extended to solvent-free system wherein salicy-... 

The Pechmann synthesis of coumarins via condensation of phenols with keto esters also involves an intramolecular hydroxyalkylation, following initial transesterification, and subsequent dehydration. It was found that H-Beta could successfully replace the sulfuric acid conventionally used as catalyst. For example, reaction of resorcinol with ethyl acetoacetate afforded methylumbelliferone (Figure 11.9), a perfumery ingredient and insecticide... 

The synthesis of substituted coumarins via Pechmann reaction catalyzed by silica gel-supported sulfuric acid (H2S04/silica gel) at 120°C under solvent-free conditions and short reaction times was described by B. M. Reddy (Scheme 8) (09MI33). 

Melamine trisulfonic acid 29 has been used as an efficient and recyclable catalyst for the synthesis of coumarins via von Pechmann condensation reaction under solvent-free conditions (Figure 5) (10JICS895). 

In the synthesis of coumarins by the von Pechmann reaction, a spiro-compound (251) was simultaneously formed from 4-chloro-2-methylphenol (and from 2,3,5-trimethylphenol). A possible mechanism for this reaction involves the formation of the lactone (252), which reacts with another molecule of the phenol. The condensation of the dicyano-ester (253) [obtained from malononitrile and ethyl cyanoacetate] with substituted o-hydroxybenzaldehydes yields substituted coumarinimines, e.g. (254).A series of 4,6,7-substituted coumarins have been prepared and assessed for their suitability in fluorescence labelling of polymers. Esters of the type PhCH CRCOaAr react with AICI3 to give coumarins, which are probably formed via dihydrocoumarins (255) by dearylation. ... 

CuFc204 nanoparticles are an efficient catalyst for the synthesis of 4-methylcoumarins via Pechmann reaction of phenols with ethyl acetoac-etate in water at room temperature (14SC697). A similar Pechmann reaction of phenols with ethyl 4,4,4-trifluoroacetoacetate catalyzed by molecular iodine affords 4-trifluoromethylcoumarins (14TL6715). Highly functionalized coumarins are formed by an iron(III) chloride-mediated cascade reaction of salicylaldehydes or 2 -hydroxyacetophenones with various activated methylene compounds (14SC1507). 

Coumarins are an important family of fragrance chemicals with herbaceous, haylike odors. The conventional methods for coumarin synthesis require drastic conditions. For example, 4-methyl-7-hydroxycoumarin 39 (Eq. 15.4.1) is prepared via the Pechmann reaction by stirring a mixture of resorcinol 37 and ethyl acetoacetate 38 in H2SO4 for 12-14 h (63). 

Sabou, R., Hoelderich, W. F., Ramprasad, D., Weinand, R. 2005. Synthesis of 7-hydroxy coumarin via the Pechmann reaction with Amberlyst ion-exchange reins as catalysts. J. Catal. 232 34-37. 

T. Wang et al. reported the synthesis of several coumarin derivatives via Pechmann-type reaction and then linked them with a cyclopentanon... 

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