Dioxirane oxidations: Taming the

w: Dioxiranes (1). a new class of powerful oxidants, have been employed to carry out a variety of synthetically useful transformations. Dioxirane reactivity appears to be earmarked by the propensity for easy electrophilic 0-atom transfer to nucleophilic substrates, as well as for 0-insertion into "unactivated " hydrocarbon C-H bonds. For a number of substrates of varying electron-donor power, ranging from a$-unsaturated carbonyls, to alkenes to sulfoxides to sulfides, the reactivity of dimethyldioxirane (la) exceeds that of peroxybenzoic acid by a factor of the order of 102; upon increasing substrate nucleophilicity, kinetic data show that the selectivity is not diminished, and actually appears to be enhanced. Despite its exceptional reactivity, high regio- and stereoselectivities can be attained in oxyfunctionalizations at hydrocarbon C-H bonds using the powerful methyl-(trifluoromethy1)dioxirane (lb); this has been applied to accomplish remarkably high regio- and stereoselective epoxidations and oxyfunctionalizations of target molecules. In these reactions, stringent steric and stereoelectronic requirements for 0-insertion seem to dictate selectivity; adoption of an FMO model provides a likely rationale