Metal ions and complexes in organic reactions. Part XIX. Response of some N-substituted o-nitrodiphenylamines to cyclisation procedures
4-Chloro-4′-methyl-2-nitrodiphenylamine, the corresponding N-methyl- and N-acetyl-compounds, and N-acetyl-4-chloro-2′-methoxy-2-nitrodiphenylamine were compared in their susceptibility to cyclisation when heated (i) alone, (ii) with iron(II) oxalate, or (iii) with triethyl phosphite. The products were phenazine and benzimidazole derivatives and (in one case, with triethyl phosphite) an azepinobenzimidazole derivative. Aromatisation of N-acetyl-5,10-dihydrophenazine was examined. Results from these and preceding investigations of cyclisations through o-nitro-groups are summarised and are discussed in relation to suggested mechanisms. A note on the preparation of o-nitrodiarylamines is included.