CHALCONE-5'-CARBOXYLIC AND FLAVANONE-6-CARBOXYLIC ACIDS

While 3-acetyl-4-hydroxybenzoic acid (1) reacts with the aldehydes 2a-c by Claisen-Schmidt reaction to the chalcone carboxylic acids 3a-c, the parent reaction with 2d is not successful. The chalcones 3a-b but not 3c can be transformed to the isomeric flavanone carboxylic acids 4a-b by common methods. 3c in MeOH/H2SO4 forms the methyl flavanone-carboxylate 4c which does not lead to the carboxylic acid of 4c by acid hydrolysis. Instead, 4c is split to chalcone carboxylic acid 3c quantitatively. 4'-nitroflavanone-6-carboxylic acid (4d) can only be obtained by condensation of the diketones 5a-b with 4-nitrobenzaldehyd (2d) as the methyl carboxylate, too. Here, instead of the expected alpha-aroylchalcone 6 or its tautomeric 3-aroylflavanone derivative, 4d is formed by hydrolytic removal of the arylcarboxylic acids 7a-b. The alkaline hydrolysis of compound 4d does not quantitatively afford the chalconecarboxylic acid 3d but results in destruction to a complex mixture of several compounds.