Oxidation with dioxiranes refers to the introduction of oxygen into organic molecules through the action of a dioxirane. Dioxiranes are well known for their oxidation of alkenes to epoxides; however, they are also able to oxidize other unsaturated functionality, heteroatoms, and alkane C-H bonds. Introduction Dioxiranes may be produced through the action of KHSO5 on carbonyl compounds. Because of their low-lying σ*O-O orbital, they are highly electrophilic oxidants and react with unsaturated functional groups, Y-H bonds (yielding oxygen insertion products), and heteroatoms. The most common dioxiranes employed for organic synthesis are dimethyldioxirane (DMD) and trifluoromethyl-methyldioxirane (TFD). The latter is effective for chemoselective oxidations of C-H and Si-H bonds. Although this class of reagents is most famous for the epoxidation of alkenes, dioxiranes have been used extensively for other kinds of oxidations as well. (1) Mechanism and stereochemistry Prevailing mechanisms Epoxidations of alkynes and allenes proceed by concerted mechanisms analogous to epoxidations of simple alkenes. Often, these epoxidized products are unstable and undergo further oxidation reactions via different mechanisms, such as Y-H insertion. Kinetic studies of heteroatom oxidations have demonstrated that their mechanisms likely proceed by an SN2 process, rather than a single-electron-transfer pathway. An example of heteroatom oxidation is the nucleophilic decomposition of DMD by N-oxides, a side reaction that regenerates the reduced starting material and converts the oxidizing agent to dioxygen and acetone. (2) Concerning the mechanism of C-H and Si-H oxidations, two mechanisms have been proposed. The debate centers on whether the oxidation takes place via concerted oxenoid-type insertion or via radical intermediates. A large body of evidence (including analogous oxidations of alkenes and peracid epoxidation) supports the concerted mechanism; however, recent observations of radical reactivity have been made. Complete retention of configuration in oxidations of chiral alkanes rules out the involvement of free, uncaged radicals. However, products of radical decomposition pathways have been observed in some DMD oxidations, suggesting radical intermediates. (3) Stereoselective variants Enantioselective dioxirane oxidations may rely on chiral, non-racemic dioxiranes, such as Shi's fructose-based dioxirane. Enantioselective oxidation of meso-diols with Shi's catalyst, for instance, produces chiral α-hydroxy ketones with moderate enantioselectivity. (4) Alternatively, an asymmetric environment may be established through the use of chiral metal complexes. For instance, coordination of sulfides to chiral, non-racemic transition-metal complexes facilitates enantioselective sulfoxidation with dioxiranes. Bovine serum albumin may also be used to establish a chiral environment for sulfoxidation. (5) Scope and limitations Dioxiranes oxidize a wide variety