Coumarins Pechmann synthesis

Parham cycloalkylation 343 Patemo-Btichi reaction 46 von Pechmann synthesis (coumarin) 322 Pellizari synthesis (1,2,4-triazole) 270 Perkin rearrangement 82 Pfitzinger synthesis (quinoline) 398 Pictet-Gams synthesis (isoquinoline) 414 Pictet-Spengler synthesis (isoquinoline) 415 Piloty-Robinson synthesis (pyrrole) 119 Pinner synthesis (pyrimidine) 467 Plancher rearrangement 128 Polonovski reaction 545 Pomeranz-Fritsch synthesis (isoquinoline) 415 Prileschajew reaction 23 Prins reaction 452 Pummerer rearrangement 26, 457... 

Alkynoates react with electron rich phenols to give coumarins with good regioselectivity in the presence of formic acid and a Pd-catalyst Yields are good even in instances where the Pechmann synthesis is reported to be unreliable <96JA6305>. 

The Pechmann synthesis of coumarins via condensation of phenols with / -keto esters also involves an intramolecular hydroxyalkylation, following initial... 

Pechmann, von, coumarin synthesis Hydrogen fluoride, anhydrous. 

The long-established Pechmann synthesis of coumarins has been revisited. The reaction of phenols with ethyl acetoacetate (EAA) occurs in better yield at lower temperatures and milder conditions in ionic liquids which act as both solvent and Lewis acid catalyst <01TL9285> and in solvent free reactions catalysed by 4-TsOH <01CL110>. Microwave irradiation of aminophenols and EAA on a solid support of graphite and montmorillonite KIO rapidly gives good yields of 4-substituted 7-aminocoumarins <01TL2791>. 

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... 

Phenols undergo acid-promoted cyclocondensation with -ketoesters to give coumarins 13 of variable substitution pattern (Von Pechmann synthesis) [30] ... 

A disadvantage of the von Pechmann synthesis is the lack of regioselectivity in coumarin formation with unsymmetrically substituted phenolic substrates. This is avoided by an alternative protocol [37], in which ortho-metalated phenolic ethers 16 are added to alkoxymethylene malonates as primary step ... 

SelectfluorTM as an efficient catalyst has been used in the Pechmann synthesis of coumarin under solvent-free conditions at 120 C. Originally, Selectfluor has been introduced commercially as a fluorinating agent (06JHC477). 

The Pechmann synthesis of 7-hydroxy 4-methyl coumarin using FLSZ and FRSZ was described by G. D.Yadav et al. (12M199).The results showed FLSZ is more active than FRSZ. 

For the synthesis of coumarins, the Pechmann reaction [145] is one of the most popular synthetic routes. As the reaction is conventionally carried out at high temperature, two microwave-assisted versions have been recently described. Besson and co-workers described the cyclocondensation of different m-amino phenols 226 with /1-ketoesters 227 on graphite/montmorillonite KIO support (Scheme 83). The use of graphite was crucial in the development of the reaction conditions. In fact, microwave irradiation of the reagents using different conditions gave poor results in terms of yields and purity. The optimized conditions, using a monomode microwave system, employed... 

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). 

Fig. 2 Representative traditional methods for coumarins synthesis, (a) Perkin synthesis (b) Pechmann-type condensation (c) Knoevenagel-type condensation...

Appel H (1935) Improved method for the synthesis of coumarins by V Pechmann s method. J Chem Soc. Abstracts 1031... 

Biswas GK, Basu K, Barua AK, Bhattacharyya P (1992) Montmorillonite clay as condensing agent in Pechmann reaction for the synthesis of coumarin derivatives. Indian J Chem 31B 628-628... 

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-... 

Some 7-aminocoumarins-4-carboxylates [60 a] were synthesized by the Pechmann reaction, by microwave irradiation of the reactants on solid supports (graphite-K10) (Scheme 8.41). Synthesis of unsubstituted coumarins (C-4 position) has been also reported [60 b]. 

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