Experiments on the synthesis of some coumarin derivatives

Evidence has been obtained that the reaction between a phenol and maleic or fumaric acid in the presence of sulphuric acid to yield a coumarin derivative, the Ponndorf reaction, is a variant of the Pechmann reaction. The scopes of the two reactions appear to be similar. Attempts to effect the oxidative cyclization of hydroxyaryl cinnamates to 4-arylcoumarins, a key step in Seshadri's scheme for the biogenesis of neoflavanoids, were unsuccessful. 4-Aryl-3,4- dihydrocoumarins, which are readily available, are smoothly converted into 4-arylcoumarins by iodine and potassium acetate in acetic acid.