Dioxiranes oxidize a wide variety of functional groups. This section describes the substrate scope of dioxirane epoxidation and the products that most commonly result.
Oxidations of alkynes, allenes, arenes, and other unique unsaturated functionality may yield epoxides or other oxidized products. Oxidation of allenes affords allene dioxides or products of intramolecular participation. Minor amounts of side products derived from additional oxidation or rearrangement were also observed.
In oxidations of heteroaromatic compounds, the products obtained depend on reaction conditions. Thus, at low temperatures, acetylated indoles are simply epoxidized in high yield (unprotected indoles undergo N-oxidation). However, when the temperature is raised to 0 °C, rearranged products are obtained.
DMD may oxidize heteroatoms to the corresponding oxides (or products of oxide decomposition). Often, the results of these oxidations depend on reaction conditions. Tertiary amines cleanly give the corresponding N-oxides. Primary amines give nitroalkanes upon treatment with 4 equivalents of DMD, but azoxy compounds upon treatment with only 2 equivalents. Secondary amines afford either hydroxylamines or nitrones.
Oxidation of nitronate anions, generated in situ from nitroalkanes, leads to carbonyl compounds in an example of an oxidative Nef reaction.
Sulfide oxidation in the presence of a single equivalent of DMD leads to sulfoxides. Increasing the amount of DMD used (2 or more equivalents) leads to sulfones. Both nitrogen and sulfur are more susceptible to oxidation than carbon-carbon multiple bonds.
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. Chiral alkanes are functionalized with retention of configuration.
Dioxiranes oxidize primary alcohols to either the aldehyde or carboxylic acid; however, DMD selectively oxidizes secondary over primary alcohols. Thus, vicinal diols may be transformed into α-hydroxy ketones with dioxirane oxidation.
Epoxidation is usually more facile than C-H oxidation, although sterically hindered allyl groups may undergo selective C-H oxidation instead of epoxidation of the allylic double bond.