Mechanistic and synthetic aspects of the acid-catalysed hydrolysis of 2,2-dimethoxy-3,4-dihydropyrans into 3,4-dihydro-α-pyrones and δ-keto esters

Abstract

Acid-catalysed hydrolysis of 2,2-dimethoxy-3,4-dihydropyrans ( 1 ) yields mixtures of δ-keto esters ( 2 ) and 3,4-dihydro-α-pyrones ( 3 ). The amount of 3 increases with increasing alkyl substitution in the 3-, 5- and 6-position of 1 and when the hydrolysis is carried out in a two-phases system of water/dichloromethane. It is shown that 3 is formed directly from 1 whereas 2 is formed directly from 1 and by methanolysis of 3 . The mechanistic and synthetic aspects of these hydrolysis reactions are discussed.