Are peroxyformic acid and dioxirane electrophilic or nucleophilic oxidants?
The electronic character of peroxyformic acid and dioxirane has been clarified by the analysis of donor-acceptor interactions in 16 transition states (TS) for the epoxidation of olefins. Is has been shown that the olefins are attacked by peroxyformic acid (PFA) in an electrophilic way. A relation of the electronic character to reactivity has been found: the more electrophilic the attack on the C=C bond is, the faster the reaction. In contrast, dioxirane (DO) has been identified as both an electrophilic and nucleophilic oxidant, depending on the substituents at the C=C double bond. The substrates with electron-withdrawing groups are attacked by DO in a nucleophilic way. These reactions have comparably low activation barriers. For instance, the acrylonitrile epoxidation with dioxirane is significantly faster than the corresponding reaction with PFA and proceeds via a transition state with a smaller extent of reaction and a larger extent of asymmetry.
Deubel
D V
DV
Department of Chemistry, University of Calgary, 2500 University Drive N.W., Calgary, Alberta, Canada T2N 1N4. deubel@ucalgary.ca