Singlet-Triplet Mechanistic Duality in the Photosubstitution of Nitrophenyl Ethers with Ethyl Glycinate. The Role of Single Electron Transfer.

Article abstract of DOI:10.1016/S0040-4020(01)90795-1

Mechanistic studies show that 4-nitroveratrole and 4,5-dinitroveratrole undergo nucleophilic aromatic photosubstitution with ethyl glycinate through an S_N2Ar* route.However, in the first case the photoreduction takes place through a singlet excited state whereas for 4,5-dinitroanisole a triplet excited state is involved.Electrochemical data for the present photoreactions reagents and for 4-nitroanisole, involved in a related photoreaction previously described by us, are reported.A mechanistic scheme, governed by a direct collapse - electron transfer competition inthe singlet excited state stage, is proposed for the nucleophilic aromatic photosubstitution reactions of nitrophenyl ethers with amine nucleophiles. Key words: Photosubstitution; Nitrophenyl Ethers; Single Electron Transfer; Redox Potentials; Mechanisms