The Baeyer Villiger Reaction

A commonly used oxidation reaction in organic synthesis is the conversion of carbonylic compounds into the corresponding esters or lactones. This reaction was discovered in 1899 by Adolf Baeyer and Victor Villiger and therefore is called the Baeyer-Villiger reaction [1]. The Baeyer-Villiger reaction is typically performed using a peroxyacid, resulting in the insertion of an oxygen atom between the carbonyl carbon and a neighboring carbon atom. For several decades the exact mechanism by which this oxygenation reaction proceeds was debated [2]. The reaction mechanism was finally elucidated in 1953 when Doering and Dorfman studied the Baeyer-Villiger oxidation of 18O-labeled benzophenone [3]. Upon oxidation of this ketone with perbenzoic acid, the labeled oxygen atom ended up as the carbonyl oxygen of the ester that was formed. This outcome confirmed a mechanism that was first proposed by Criegee [4] and involves formation and decay of a so-called "Criegee intermediate." This tetrahedral intermediate is formed by a nucleophilic attack of the peroxyacid onto the ketone (Fig. 3.1). Subsequent decay of this labile intermediate involves migration of a substituent from the carbonyl carbon, yielding an ester or lactone.

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. Unsubstituted groups (e.g. a methyl) adjacent to the carbonyl function represent poor migrating groups while highly substituted groups (e.g. tertiary alkyl) have a good migratory aptitude. An additional attractive feature of the Baeyer-Villiger reaction is that the migrating group will typically retain its configuration. This allows effective and selective oxidation reactions. However, a major drawback of the reaction is the intrinsic need for a potent and therefore hazardous oxidizing agent. The classical approach to perform a Baeyer-Villiger reaction includes the use of organic

Criegee intermediate Fig. 3.1 The Baeyer-Villiger reaction proceeds via formation and subsequent rearrangement of a Criegee intermediate.

Criegee intermediate Fig. 3.1 The Baeyer-Villiger reaction proceeds via formation and subsequent rearrangement of a Criegee intermediate.

peroxyacids as catalyst. In addition to the fact that these reactive compounds have to be handled with care, they are also relatively expensive. This has triggered development of more gentle catalytic systems that enable Baeyer-Villiger reactions, such as the use of hydrogen peroxide-dependent catalysts (see [5] for a recent review). An obvious alternative "green chemistry" approach would be the use of a biocatalyst that is able to catalyze Baeyer-Villiger reactions.

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