Solid acid catalysis of tandem isomerization-lactonization of olefinic acids

The conversion of unsaturated acids to γ-lactones is catalyzed by the solid sulfonic acid catalysts Amberlyst-15 and Nafion SAC-13 in refluxing chlorobenzene. For 3- and 4-enoic acids, in which double bond migration is not required for γ-lactone formation, yields are 95–100%. For 5-, 6-, 9-, and 10-enoic acids, the lactone yield decreases from 95% to 25% as the distance between the olefin and carboxylic acid groups increases. Amberlyst-15 is the preferred catalyst in these reactions because of its lower cost and reusability.

Graphical abstractThe 5-, 6-, 9-, and 10-enoic acids (a) undergo tandem olefin migration followed by cyclization to give γ-lactone (b) products in 25-95% yields in the presence of Amberlyst-15 in refluxing chlorobenzene. In all of these reactions, the δ-lactone (c) forms initially and then rearranges to the final γ-lactone (b) product.Figure optionsDownload full-size imageDownload as PowerPoint slide