TOPOLOGICALLY CONTROLLED COULOMBIC INTERACTIONS, A NEW TOOL IN THE DEVELOPING OF NOVEL REACTIVITY - PHOTOCHEMICAL AND ELECTROCHEMICAL CLEAVAGE OF PHENYL ALKYL ETHERS

The hypothesis that a specific placement of a positive charge would dramatically alter the behavior of a charged intermediate has been tested. Phenyl ethers substituted by electron-attracting groups do not undergo reductive fragmentation. However, related alpha-piperidino-omega-(4-substituted-phenoxy)-alkanes give alkyl ether photocleavage when the linker between the redox centers is short, or the usual substitution-reduction photochemistry when it is long. Mechanistic experiments suggest that the photofragmentation process operates through space intramolecular electron transfer to the triplet aromatic chromophore and that a coplanar relative orientation of the alkyl ether bond and the phenyl ring is compulsory for the photofragmentation to be observed. Configuration interaction AM1 calculations justify the described facts, indicating that the fragmentation process is only operative when a Coulombic stabilization of a sigma* intramolecular electron transfer excited state is produced. Electrochemical studies carried out with the corresponding quaternary salts (intermolecular generation of the phenyl ether radical anion) confirm the conclusions derived from the photochemical experiments.