Direct Oxidative Cyclization of 3-Arylpropionic Acids to 3,4-Dihydrocoumarins: Reinvestigation of the Reaction Mechanism.

Instigated by olfactory analysis of odorant molecules, the constitutions of 3,4-dihydrocoumarins prepared by PIFA-based oxidative cyclizations of 3-arylpropionic acids were revised by means of 2D NMR and X-ray analysis. Supported by computational analysis, the migratory mechanism of intermediate spirolactonic cations has been amended: 1,2-alkyl shifts instead of 1,2-carboxylic shifts were selectively obtained.