Photochemistry of N-acyl-2-nitrodiphenylamines. A novel photochemical synthesis of phenazine N-oxides
In contrast with 2-nitrodiphenylamines and their N-alkyl derivatives, N-acetyl- and N-benzoyl-2-nitrodiphenylamines are converted into phenazine N-oxides by u.v. irradiation. The requirement of N-acyl groupings is best explained in terms of oxygen transfer from the nitro-group to the amide carbonyl group. The reaction has been applied to the synthesis of some condensed pyrazine N-oxides (imidazo- and thieno-quinoxaline N-oxides).