"The Baeyer-Villiger oxidation involves an initial attack of a peroxy acid at the carbonyl carbon, which is followed by migration of an adjacent group from the carbonyl carbon to the electron-deficient oxygen of the peroxy acid moiety. The rearrangement proceeds in a concerted manner and is stereospecific. Thus, a chiral migrating group maintains its chiral integrity in the product. The overall reaction represents an insertion of an oxygen between the carbonyl carbon and the migrating group. The Baeyer-Villiger reaction applied to acylic ketones provides esters, whereas cyclic ketones furnish lactones. The observed relative ease of migration, tert-alkyl > sec-alkyl > phenyl > n-alkyl > methyl, reflects the ability of the migrating group to accommodate a partial positive charge at the transition state. In addition to electronic factors, steric and conformational constraints as well as reaction conditions may influence the ease of migration. However, the regiochemistry can usually be controlled by proper choice of migrating group. … Thus, the Baeyer-Villiger oxidation is not only stereospecific but frequently regioselective. By controlling reaction conditions and by proper choice of the peroxy acid, it is often possible to favor the Baeyer-Villiger reaction over epoxidation."