Intramolecular acetalization of 5-hydroxy ketones and enones. A novel transformation of important prostaglandin intermediates under acidic conditions
Intermediates in the synthesis of ω-tetranor 16-aryloxy prostaglandins, which are 5-hydroxy enones, undergo quantitative intramolecular transformation into cyclic methyl acetals in acidic methanolic solution. The reaction proceeds via the corresponding 5-hydroxy-3-methoxy ketones, which partly exist as hemiacetals. The structure of the compounds investigated was elucidated by 1H NMR spectroscopy and by X-ray analysis of the acetal (11).