Perkin-type condensation

This method allowed also the synthesis of xylerythrins (IV, Scheme 4b), through a Perkin-type condensation of the terphenylquinone with... 

Decarboxylation of a-keto acids. Phenylglyoxylic acid is decarboxylated smoothly by refluxing in benzene with benzoic anhydride and pyridine. Other anhydrides can be used but benzoic anhydride is preferred because Perkin-type condensations... 

Perkin-type condensations of m-nitrobenzaldehyde and of phthalic anhydride are formulated. In the second case sodium acetate is taken in catalytic amount, and the water produced in the formation of benzalphthalide distills as formed. 

Intramolecular aldol/Perkin type condensation of orf/to-formylaryloxyacetic acids and arylthioacetic esters produces benzofuran- and benzothiophene-2-esters respectively, as illustrated below. The synthesis can be performed in one pot, thus ortfto-hydroxyaryl-aldehydes or -ketones, are 0-alkylated with a-halo-ketones, then intramolecular aldol condensation in situ produces 2-acyl or 2-aroyl-benzofurans. ° For benzothiophenes, the ring-closure substrates can also be obtained via methyl thioacetate displacement of fluoride from orf/to-fluoro-araldehydes. ... 

Intramolecular aldol/Perkin type condensation of aryloxyacetic acids and arylthioacetic esters produces benzofuran and benzothiophene-2-esters respectively. The examples shown illustrate contrasting methods - classical and modem - for the preparation of the required starting materials. 

Structure (155) for xylerythrin was confirmed by synthesis involving a Perkin-type condensation between polyporic acid and (4-hydroxy-phenyl)acetic aicid (329). This reaction, performed in acetic anhydride... 

The reaction probably proceeds by an initial cyclisation of the acylamlnoacetic acid, followed by a Perkin type of condensation of the aldehyde with the active methylene unit ... 

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

A further route to the cycloocta[l,2-c 5,6-c ]difuran system makes use of a Perkin-type reaction. Condensation of furan-3,4-dicarboxaldehyde with furan-3,4-diacetic acid in acetic anhydride and triethylamine at room temperature, followed by esterification with methanol and sulfuric acid, gave... 

The forward synthetic reaction is a base-catalysed condensation reaction between two carbonyl compounds, the aldol condensation leading to -hydroxy-aldehydes or / -hydroxyketones followed by dehydration. This sequence is one of the most important carbon-carbon bond forming reactions, and aldol-type condensation reactions are considered in a number of other sections of the text, for example, the Doebner reaction (Section 5.18.3, p. 805), the Knoevenagel reaction (Section 5.11.6, p. 681), the Perkin reaction (Section 6.12.3, p. 1036) and the Robinson annelation reaction (Section 7.2). 

Diphenylocta-1,3,5,7-tetraene can be prepared (Expt 6.140) by condensing two mols of cinnamaldehyde with succinic acid in the presence of acetic anhydride and lead oxide, in a reaction which bears similarities with those of the Perkin type discussed above. 

The generally accepted mechanism for the Perkin reaction is shown in Scheme 2. Much of the early woik leading to this view, which was the result of numerous investigations spanning a period of greater than SO years, has been reviewed in some detail. Formation of the anhydride enolate (1) and aldol-type condensation generates the alkoxide anhydride (2). Intramolecular acylation provides an acetoxycaibox-ylate (3), which forms a mixed anhydride elimination of acetic acid and hydrolysis affords the unsatu-... 

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. ... 

The Perkin condensation is an aldol-type condensation in which an aromatic aldehyde (ArCHO) reacts with a carboxyUc acid anhydride, (RCH2C0)20, to give an a,j8-unsaturated acid (ArCH = CRCO2H). The catalyst that is usually employed is the potassium salt of the carboxylic acid (RCH2CO2K). (a) Outline the Perkin condensation that takes place when benzaldehyde reacts with propanoic anhydride in the presence of potassium propanoate. (b) How would you use a Perkin condensation to prepare />-chlorocinnamic acid, />-CIC6H4CH = CHC02H ... 

The entire manifold of aldol-type condensation reactions. The aldol condensation itself (Equation 9.45, el seq) and all of those in Table 9.5 (viz. the Claisen, Stobbe, Perkin, and Knovenagel condensation reactions and the Robinson annulation). 

In what amounts to a biogenetically patterned approach, a synthesis of xylerythrin (7 a) has been reported involving condensation between polyporic acid (100) and p-hydroxyphenylacetic acid (d) this Perkin-type reaction proceeds via the 4-oxo-2-enoic acid intermediate (101). 

A complementary procedure for the preparation of ylidenebutenolides from maleic anhydrides, which has several advantages over the Grignard-and Perkin-type approaches, employs phosphoranylides. This approach was first applied in the synthesis of alkylidenephthalides e.g. 162) by reaction between phthalic anhydride and the appropriate triphenylphos-phorane 133). Interestingly, the condensations involving phosphoranes... 

Condensation reactions of the aldol type play an important part in heterocyclic chemistry. There are a large number of condensation reactions that are closely related to the aldol condensation. Each of these reactions has its own name Claisen, Dieckmann, Doebner, Knoevenagel, Perkin, to mention a few, but the chemistry is essentially the same as that of the aldol condensation. 

---