Reductively activated ‘polar’ nucleophilic aromatic substitution. A new mechanism in aromatic chemistry?

Electrochemical studies indicate that although the reactions of p- dinitrobenzene and p-nitrobenzonitrile with phenolate or phenol in DMF show radical features, they can not be attributed to the direct reaction of the nucleophile on the substrate radical anion. Mechanistic studies suggest that in spite of its different behavior in front of radical scavengers or irradiation, all polyfluoronitrobenzenes react with methanol in aqueous solution following a second stage rate determining “polar” SNAr mechanism. The reported facts are not compatible with the previously proposed (for some of these reactions) SRN2 mechanism. However, reductive activation is feasible in certain cases but substrate radical anion formation is not responsible for it. Topologically controlled coulombic interactions (TCCI) have been used to achieve reductively activated SNAr reactions on otherwise unreactive nitrophenyl ethers. A mechanistic rationale is discussed. © 1995 IUPAC