Baeyer-Villiger oxidation promoted by reaction of peracids with cyclic oxocarbenium ions generated in situ from internal hemiketals.

[reaction: see text] Reactive cyclic oxocarbenium ions, generated in situ from internal hemiketals, undergo Baeyer-Villiger oxidation upon exposure to m-chloroperbenzoic acid leading, after hydrolysis of the resultant lactones, to acyclic fragments for use in natural product synthesis.