Oxidation of α,β-unsaturated ketones with alkaline hydrogen peroxide produces the corresponding keto epoxides in good yields. This nucleophilic epoxidation proceeds via an initial Michael-type addition of the hydroperoxide anion to the enone system … Treatment of enones with basic tert-butyl hydroperoxide provides an alternative route for epoxidation of enones when the alkaline hydrogen peroxide procedure fails.
Dirnethyldioxirane (DMDO) is a mild reagent for epoxidation under neutral conditions of electron-rich as well as of electron-deficient alkenes. Moreover, dimethyldioxirane is often the oxidant of choice for the preparation of labile epoxides. … Methyl(trifluoromethyl)dioxirane (TFDO), … is more reactive than DMDO by a factor of ~600. … TFDO can be used to regioselectively oxidize tertiary over secondary C-H bonds via an “oxenoid” (butterfly) mechanism.
Chloroiodomethane on treatment with methyllithium-lithium bromide or n-butyllithium at low temperature undergoes lithium iodide exchange to form a lithium chlorocarbenoid species [LiCHCl]. This highly reactive "carbanion" intermediate can be intercepted by the carbonyl group of aldehydes or ketones before it undergoes α-elimination to generate carbene and LiC1. Displacement of chloride from the initially formed carbonyl adducts furnishes the corresponding epoxides in high yields.
Although epoxidation of cyclic alkenes occurs preferentially from the less hindered side, the presence of a polar substituent near the double bond may reverse the facial direction of attack by the peroxide.
Straight-chain allylic alcohols have been crucial to the development of stereoselective syntheses of complex natural products since they can be converted stereoselectively into epoxides and via further elaboration of these into a host of functionalized compounds of predictable stereochemistry.