Dioxirane oxidations: Taming the reactivity-selectivity principle

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 regioand 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 regioand 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.