Phenylacetic acid Perkin reaction with

Here the phenylacetic anhydride, possessing more reactive a-hydrogen atoms, condenses with benzaldehyde to give a-phenylcinnamic acid. The preparation of the latter is an example of the Oglialoro modiflcation of the Perkin reaction. 

Perkin reaction of this aldehyde with phenylacetic acid gives a mixture of the benzothiophene 13 (57%) and the thiocoumarin 14 (40%). ... 

The reaction of benzaldehyde with phenylacetic acid to produce a mixture of the a-carboxylic acid derivatives of Z- and -stilbene a form of aldol condensation known as the Perkin reaction, is effected by heating a mixture of the components with acetic anhydride and triethylamine. In the course of the reaction the phenylacetic acid is probably present both as anion and as the mixed anhydride resulting from equilibration with acetic anhydride. A reflux period of 5 h specified in an early procedure has been shortened by a factor of 10 by restriction of the amount of the volatile acetic anhydride, use of an excess of the less expensive, high-boiling aldehyde component, and use of a condenser that permits some evaporation and consequent elevation of the reflux temperature. 

Phthalic anhydride, when used as the carbonyl component in the Perkin reaction, affords, on treatment with acetic anhydride and potassium acetate, phthalylacetic acid (15 equation 12).24 a-Arylacetic acids also react with aromatic aldehydes to afford a-arylcinnamic acids (Ogliaro modification of the Perkin condensation, equation 7) 1 this type of reaction presumably involves die formation of the mixed anhydride of phenylacetic acid and acetic acid and/or phenylacetic anhydride. This modification is also illustrative of the equilibrium that is established between acid, acid salt and acid anhydrides under the conditions of the reaction. 

Under the usual conditions of the Perkin reaction, cinnamaldehyde gives an excellent yield of 5-phenyl-2,4-pentadienoic acid 890 but decarboxylation occurs when it is heated with phenylacetic acid and acetic anhydride in the presence of lead(n) oxide, 1,4-diphenyl-1,3-butadiene being formed in 30% yield,891 and under these conditions two equivalents of cinnamaldehyde and one of succinic acid give l,8-diphenyl-l,3,5,7-octatetraene.892... 

The most important modification of the Perkin reaction was developed by Oglialoro using the sodium salt of acetic acid (e.g., phenylacetic acid, phenoxyacetic acid ) in condensation with acetic anhydride and an aldehyde (e.g., benzaldehyde, paraldehyde ). This type of reaction is referred to as the Perkin-Oglialoro reaction,Perkin-Oglialoro condensation, or Oglialoro modification. Other modifications include the use of different bases as the catalysts, (e.g., NaB(OMe)4-LiCl, CaH2, CsOAc, and CsF ), the use of microwave irradiation and cesium acetate or fluoride in combination with a small amount of pyridine as catalyst and the continuous distillation of acetic acid to enhance the conversion rate. ... 

A one-pot two-step synthesis of hydroxystilbenes with trans selectivity was developed through a modified Perkin reaction between benzaldehydes and phenylacetic acids bearing 4- or 2-hydroxy substitution at the aromatic ring [67]. The reaction was performed under mild conditions in the presence of piperidine-methylimidazole and polyethylene glycol under microwave irradiation. As a result, 71% yield of ( )-4-chloro-4 -hydroxy-3 -methoxystilbene from 4-hydroxy-3-methoxybenzaldehyde and 4-chlorophenylacetic acid was obtained. A microwave-induced one-pot process for the preparation of arylethenes has been patented [118]. For the preparation of a series of arylethenes (I R -R = H, OH, OMe, AcO, halo, NO2 R, R, R = OH, AcO R= H, substituted aryl), reaction of 2- or 4-hydroxy substituted cinnamic adds or derivatives in the presence of a base, under reflux or microwave irradiation, has been used. For example, a mixture of a-phenyl-4-hydroxy-3-methoxycinnamic acid, NaHC03, methylimidazole, and polyethylene glycol was microwaved at 200 W and 180 °C for 10 min to give 96% 4-hydroxy-3-methoxystilbene. 

Azacoumarins, e.g., 41, represent possible intermediates to the phenyl-substituted pyrano[2,3-b]pyridines. Thus, Perkin reaction of the acetylpyridone 15 with phenylacetic acids formed azacoumarins in fairly good yields. Attempts to reduce the carbonyl function of the lactone ring to the methylene function were unsuccessful. Nevertheless, the imidazolinones 42 derived from these azacoumarins were synthesized. 

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