Singlet-triplet mechanistic duality in the photosubstitution of nitrophenyl ethers with ethyl glycinate. The role of single electron transfer.

Mechanistic studies show that 4-nitroveratrole and 4,5-dinitroveratrole undergo nucleophilic aromtic photosubstitution with ethyl glycinate through an SN2Ar* route. However, in the first case the photoreaction 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 in the singlet excited state stage, is proposed for the nucleophilic aromatic photosubstitution reactions of nitrophenyl ethers with amine nucleophiles. © 1992.