4- Hydroxyalkanoic acids, lactones from

Zeolites have also been described as efficient catalysts for acylation,11 for the preparation of acetals,12 and proved to be useful for acetal hydrolysis13 or intramolecular lactonization of hydroxyalkanoic acids,14 to name a few examples of their application. A number of isomerizations and skeletal rearrangements promoted by these porous materials have also been reported. From these, we can underline two important industrial processes such as the isomerization of xylenes,2 and the Beckmann rearrangement of cyclohexanone oxime to e-caprolactam,15 which is an intermediate for polyamide manufacture. Other applications include the conversion of n-butane to isobutane,16 Fries rearrangement of phenyl esters,17 or the rearrangement of epoxides to carbonyl compounds.18... 

Carboxylic esters, especially lactones, are conveniently obtained via the pyridyl thioesters (18). Some examples are given in Scheme 1. The 2-pyridyl thiol ester method can be further improved if silver ions (AgC104) are used as activators. Corey and Brunelle have also introduced other heterocyclic disulfides, and (19) was found to be superior to other reagents tested for the formation of lactones from w-hydroxyalkanoic acids. 

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