Arylcinnamic acids

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

An example of such a reaction is the Pschorr reaction, in which 2-amino-a-arylcinnamic acid (195) yields a phenanthrene (196). The reaction proceeds in 10-20% yield on irradia-... 

The only by-product is the 2-iodo-a-arylcinnamic acid as a product of the reaction of the parent diazonium ion with the iodide. This can be also converted to 53 by photoarylation, see Chapter 7. 

As a typical intermolecular carbopalladation and termination, hydroarylation of alkynes are carried out extensively in the presence of HCO2H as a hydride source. Formation of regioisomers is observed in the reaction of asymmetric alkynes, and ratios depend on the nature of the substituents. High regioselectivity was observed in the reaction of the tertiary propargylic alcohol 14 to give 15 as a major product [5]. The (Z)-2-arylcinnamates 17, rather than 3-arylcinnamate 18, was obtained by the hydroarylation of methyl phenylpropiolate (16) [6]. 3-Substituled quinoline 21 was prepared by the regioselective hydroarylation of 19, followed by treatment of 20 with an acid without isolation [6]. 

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