Concerning the reactivity of dioxiranes. Observations fromexperiments and theory

The challenging hypothesis of a “biphilic” (i.e., electrophilic vs nucleophilic) character for dioxirane
reactivity, which envisages that electron-poor alkenes are attacked by dioxiranes in a nucleophilic fashion,
could not be sustained experimentally. Rate data, which estimate Hammett “rho” values for the epoxidation
of 3- or 4-substituted cinnamonitriles XâPhsCHdCHsCN, unequivocally allow one to establish that
dioxiranes epoxidize electrophilically even alkenes carrying electron-withdrawing groups. The greater
propensity of methyl(trifluoromethyl)dioxirane TFDO (1b) to act as an electrophilic oxidant with respect to
dimethyldioxirane DDO (1a) parallels the cathode reduction potentials for the two dioxiranes, as measured
by cyclic voltammetry. A simple FMO approach for alkene epoxidation is helpful to conceive a likely rationale
for the greater oxidizing power of TFDO as compared to DDO.