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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. [1] This migration step is thought to be the rate determining step. [2] [3] Finally, deprotonation of the oxocarbenium ion produces the ester. [1] Reaction mechanism of the Baeyer-Villiger ...
The following scheme shows the epoxidation of cyclohexene with mCPBA. The epoxidation mechanism is concerted: the cis or trans geometry of the alkene starting material is retained in the epoxide ring of the product. The transition state of the Prilezhaev reaction is given below: [5]
The reaction proceeds through what is commonly known as the "butterfly mechanism", first proposed by Bartlett, wherein the peracid is intramolecularly hydrogen-bonded at the transition state. [5] Although there are frontier orbital interactions in both directions, the peracid is generally viewed as the electrophile and the alkene as the ...
However it has been shown that for medium-sized rings (eight and nine) peracid oxidizers show reverse selectivity, while vanadium catalyzed reactions continue to show formation of the syn epoxide. [14] Although it is the least reactive metal catalyst for epoxidations, vanadium is highly selective for alkenes with allylic alcohols.
The most common use of organic peroxy acids is for the conversion of alkenes to epoxides, the Prilezhaev reaction. Formation of an epoxide from an alkene and a peroxycarboxylic acid. Another common reaction is conversion of cyclic ketones to the ring-expanded esters using peracids in a Baeyer-Villiger oxidation .
The mechanism of epoxidation with dioxiranes likely involves concerted oxygen transfer through a spiro transition state. As oxygen transfer occurs, the plane of the oxirane is perpendicular to and bisects the plane of the alkene pi system. The configuration of the alkene is maintained in the product, ruling out long-lived radical intermediates.
The reaction proceeds via what is commonly known as the "Butterfly Mechanism". [13] The peroxide is viewed as an electrophile, and the alkene a nucleophile. The reaction is considered to be concerted. The butterfly mechanism allows ideal positioning of the O−O sigma star orbital for C−C π electrons to attack. [14]
The reaction mechanism of the Sharpless dihydroxylation begins with the formation of the osmium tetroxide – ligand complex (2). A [3+2]-cycloaddition with the alkene (3) gives the cyclic intermediate 4. [9] [10] Basic hydrolysis liberates the diol (5) and the reduced osmate (6).