Acid-catalysedhydrolysis of 2,2-dimethoxy-3,4-dihydropyrans () yields mixtures of δ-keto esters () and 3,4-dihydro-α-pyrones (). The amount of increases with increasing alkyl substitution in the 3-, 5- and 6-position of and when the hydrolysis is carried out in a two-phases system of water/dichloromethane. It is shown that is formed directly from whereas is formed directly from and by methanolysis