An ideal oxidant should be highly reactive, selective, and environmentally benign. It should transform a broad range of substrates with diverse functional groups, preferably under catalytic conditions, and be readily generated from commercially available and economical starting materials. Of course, such an ideal oxidant has not yet been invented; however, the dioxiranes, which have risen to prominence during the past few decades, appear to fulfill these requirements in many respects. These three membered ring cyclic peroxides are very efficient in oxygen transfer, yet very mild toward the substrate and product. They exhibit chemo-, regio-, diastereo-, and enantioselectivities, act catalytically, and can be readily prepared from a suitable ketone (for example, acetone) and potassium monoperoxysulfate (2KHSO5 · K2SO4 · Caroate®, Oxone®, or Curox®), which are low-cost commercial bulk chemicals. Throughout the text KHSO5 is used to specify this oxygen source, rather than refer to one of the commercial trade names.
Isolated dioxiranes (as solutions in the parent ketones) perform oxidation under strictly neutral conditions so that many elusive oxyfunctionalized products have been successfully prepared in this way for the first time. Epoxidations, heteroatom oxidations, and X-H insertions constitute the most investigated oxidations by dioxiranes. An overview of these transformations is displayed in a rosette scheme. These preparatively useful oxidations have been extensively reviewed during the last decade in view of their importance in synthetic chemistry.
This chapter deals mainly with the epoxidation of carbon-carbon double bonds [π bonds in simple alkenes and with these electron donors (ED), electron acceptors (EA), and with both ED and EA] with either isolated or in situ generated dioxiranes. In view of the vast amount of material on alkene oxidation, the epoxidation of the double bonds in cumulenes (allenes, acetylenes) and arenes is covered in a separate chapter, together with the oxidation of heteroatom functionalities (nonbonding electron pairs), X-H insertions (σ bonds) and transition-metal complexes.