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Concept
Baeyer–Villiger oxidation
Summary
The Baeyer–Villiger oxidation is an organic reaction that forms an ester from a ketone or a lactone from a cyclic ketone, using peroxyacids or peroxides as the oxidant. The reaction is named after Adolf von Baeyer and Victor Villiger who first reported the reaction in 1899.
In the first step of the reaction mechanism, the peroxyacid protonates the oxygen of the carbonyl group. This makes the carbonyl group more susceptible to be attacked by the peroxyacid. Next, the peroxyacid attacks the carbon of the carbonyl group forming what is known as the Criegee intermediate. Through a concerted mechanism, one of the substituents on the ketone group migrates to the oxygen of the peroxide group while a carboxylic acid leaves. This migration step is thought to be the rate determining step. Finally, deprotonation of the oxocarbenium ion produces the ester.
The products of the Baeyer–Villiger oxidation are believed to be controlled through both primary and secondary stereoelectronic effects. The primary stereoelectronic effect in the Baeyer–Villiger oxidation refers to the necessity of the oxygen-oxygen bond in the peroxide group to be antiperiplanar to the group that migrates. This orientation facilitates optimum overlap of the σ orbital of the migrating group to the σ* orbital of the peroxide group. The secondary stereoelectronic effect refers to the necessity of the lone pair on the oxygen of the hydroxyl group to be antiperiplanar to the migrating group. This allows for optimum overlap of the oxygen nonbonding orbital with the σ* orbital of the migrating group. This migration step is also (at least in silico) assisted by two or three peroxyacid units enabling the hydroxyl proton to shuttle to its new position.
The migratory ability is ranked tertiary > secondary > aryl > primary. Allylic groups are more apt to migrate than primary alkyl groups but less so than secondary alkyl groups. Electron-withdrawing groups on the substituent decrease the rate of migration. There are two explanations for this trend in migration ability.
Official source
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