Oxidation with dioxiranes

Dioxiranes are electrophilic oxidants that react more quickly with electron-rich than electron-poor double bonds; however, both classes of substrates can be epoxidized within a reasonable time frame.

The mechanism of epoxidation with dioxiranes likely involves concerted oxygen transfer through a spiro transition state.

In addition, the spiro transition state has been used to explain the selectivity in enantioselective epoxidations with chiral ketones.

When racemic 3-isopropylcyclohexene was subjected to DMD oxidation, the trans epoxide, which resulted from attack on the less hindered face of the double bond, was the major product.

[6] Enantioselective dioxirane epoxidation is critical in a synthetic sequence leading to an analogue of glabrescol.

Peracids generate acidic byproducts, meaning that acid-labile substrates and products must be avoided.

[8] Some methods are well-suited to the oxidation of electron-rich or electron-poor double bonds, but few are as effective for both classes of substrate as dioxiranes.

Dioxiranes may be prepared and isolated or generated in situ from ketones and potassium peroxymonosulfate (Oxone).

The functional group compatibility of dioxiranes is limited somewhat, as side oxidations of amines and sulfides are rapid.

(10)Although alkanes are typically difficult to functionalize directly, C-H insertion with TFD is an efficient process in many cases.

The order of reactivity of C-H bonds is: allylic > benzylic > tertiary > secondary > primary.

Often, the intermediate alcohols produced are oxidized further to carbonyl compounds, although this can be prevented by trapping in situ with an anhydride.

[2] A variety of alternative heteroatom oxidation reagents are known, including peroxides (often employed with a transition metal catalyst) and oxaziridines.

Although chiral dioxiranes do not provide the same levels of enantioselectivity as other protocols, such as Kagan's sulfoxidation system,[18] complexation to a chiral transition metal complex followed by oxidation affords optically active sulfoxides with good enantioselectivity.

These substrates are resistant to many epoxidation reagents, including oxaziridines, hydrogen peroxide, and manganese oxo compounds.