Electrochemical behavior of N-oxyphthalimides: Cascades initiating self-sustaining catalytic reductive N-O bond cleavage

N-oxyphthalimides are stable and easily accessible compounds that can produce oxygen radicals upon 1-electron reduction. We present a systematic study of electrochemical properties of N-oxyphthalimide derivatives (PI-ORs) in DMF by cyclic voltammetry. In all cases, electron transfer to the substrate leads to decomposition of the intermediate radical anion via the N-O bond cleavage. In the case of benzyloxyphthalimide or its derivatives containing electron-donating substituents, reductive electron transfer induces the chain decomposition of the substrate to phthalimide ( PI) radical-anion and the corresponding carbonyl compound. The PI radical-anion product is a powerful reductant that can transfer an electron to the reactant PI-OR, thus establishing a catalytic cycle for reductive N-O scission. This self-catalytic process is reflected in a considerable decrease in the reduction current for the substrate (<1e(-)/molecule). By contrast, reductive fragmentations of benzyl derivatives containing electron-withdrawing substituents in the aromatic ring or at the benzylic position, as well as tosyl and alkyl derivatives, occur via a 1-electron mechanism. A sequence of N-O and C-C scissions was engineered to support the intermediacy of O-centered radicals in these processes.