Baeyer-Villiger Oxidation

Theory and Defination :

The Baeyer–Villiger oxidation is an organic reaction in which a ketone is oxidized to an ester by treatment with peroxy acids or hydrogen peroxide.Key features of the Baeyer–Villiger oxidation are its stereospecificity and predictable regiochemistry. It is named after the German chemist Johann Friedrich Wilhelm Adolf von Baeyer (1835–1917) and the Swiss chemist Victor Villiger (1868–1934).

Genaral Reaction :

Reagents typically used to carry out this rearrangement are meta-chloroperoxybenzoic acid (mCPBA), Disodium phosphate or sodium bicarbonate is often added as a buffering agent to prevent transesterification or hydrolysis.

Mechanism

The reaction is initiated by addition of peracid to the ketone. The addition is catalyzed by protons originating from the peracid or the carboxylic acid formed during the reaction.

Fig.1: Addition of peracid to ketone

At the same time, the peracid functions as a nucleophile by attacking the carbonyl carbon with the terminal oxygen atom, thereby forming an α-hydroxyperoxy ester.

Fig.2: Hydroxyperoxy ester formation

Contrary to the behavior of peracids and simple hydroperoxides, hydroxyperoxy esters spontaneously decompose already at room temperature. 1,2-Migration of the the substituents R' or R" produces an ester and a carboxylic acid derived from the peracid.

Fig.3: Substituent migration

Migration of the substituent takes place with retention, i.e. a pure enantiomeric ketone produces a pure enantiomeric ester.

Examples :

1)epi-cytoxazone and the αα-hydroxy-ββ-amino acid derivatives from ketones.

Application :

1.The Baeyer-Villiger reaction is widely appreciated in organic synthesis as it is applicable to a broad range of carbonylic compounds while the moiety that will migrate during the reaction can also be predicted to some extent.
2.An additional attractive feature of the Baeyer-Villiger reaction is that the migrating group will typically retain its configuaration. This allows effective and selective oxidation reactions. However, a major drawback of the reaction is the intrinsic need for a potent and therefore hazardous oxidising agent.
3.The classical approach to perform a Baeyer-Villiger reaction includes the use of organic peroxyacids as catalyst. In addition to the fact that these reactive compounds have to be handled with care, they are also relatively expensive.