Baeyer-Villiger Oxidation
The Baeyer-Villiger oxidation is a transformation in organic chemistry that inserts an oxygen atom between the carbonyl carbon of a ketone and an adjacent carbon atom:
The reaction is often performed using a peroxyacid such as mCPBA (meta-chloroperbenzoic acid). Other oxidants can be used under certain circumstances including hydrogen peroxide, peroxyacetic acid, peroxytrifluoroacetic acid, and other organic peroxy acids and peroxides.
Mechanism:
The mechanism involves the acid-promoted nucleophilic attack of the carbonyl carbon atom of the ketone starting material by the oxygen atom of the peroxy acid that is not bonded to carbon. This produces the tetrahedral intermediate known as the Criegee intermediate. A pair of electrons on the oxygen atom in the species formed is then used to form a carbon oxygen double bond, and one of the alkyl groups undergoes a 1,2 shift from the carbon atom of the carbonyl to the oxygen atom of the peroxy acid. The carboxylate analog of the peroxy acid is eliminated and the resulting ester product is formed.
Regio- and Stereochemistry:
The regiochemistry and stereochemistry of the reaction products are highly predictable. The group that migrates is the group that is best able to stabilize a developing positive charge in the transition state. Usually, but not always, the more highly substituted group will migrate. If one of the groups is particularly capable of stabilizing a positive charge, such as allyl or benzyl, it will usually migrate even if it is not the most highly substituted group. When the carbon atom that migrates is an asymmetric (i.e. chiral) center, the reaction usually proceeds with retention of configuration.
When aldehydes are subjected to the reaction conditions the hydrogen atom attached to the carbonyl carbon usually migrates and gives rise to the carboxylic acid. If the group attached to carbon is particularly well suited to stabilize a positive charge however, that group may undergo migration to produce the formic acid ester (i.e. formate).
References:
Baeyer, A.; Villiger, V. “Einwirkung des Caro’schen Reagens auf Ketone” (abstract). Ber. 1899, 32 (3): 3625–3633.
Burton, J.W.; Clark, J.S.; Derrer, S.; Stork, T.C.; Bendall, J.G.; Holmes, A.B. “Synthesis of Medium Ring Ethers. 5. The Synthesis of (+)-Laurencin” (Abstract). J. Am. Chem. Soc. 1997, 119 (32): 7483–7498.
M. A. Goodman, M. R. Detty. “Selenoxides as Catalysts for Epoxidation and Baeyer-Villiger Oxidation with Hydrogen Peroxide” Synlett, 2006, 1100-1104.
S. Murahashi, S. Ono, Y. Imada, Angew. “Asymmetric Baeyer-Villiger Reaction with Hydrogen Peroxide Catalyzed by a Novel Planar-Chiral Bisflavin” Chem. Int. Ed., 2002, 41, 2366-2368.
G. A. Olah, Q. Wang, N. J. Trivedi, G. K. S. Prakash. “Baeyer-Villiger Oxidation of Ketones to Esters with Sodium Percarbonate/Trifluoroacetic Acid”, Synthesis, 1991, 739-740.
Michael Renz, Bernard Meunier (1999). “100 Years of Baeyer-Villiger Oxidations”. European Journal of Organic Chemistry 1999 (4): 737–750.