Competition between Nucleophilic Attack and Electron Transfer in the Reaction of Indoledione Imine N-oxides with Primary Aromatic Amines

2-Methyl-3,5-dioxo-2-phenyl-3,5-dihydro-2H-indole 1-oxide (1) and 2-methyl-3,7-dioxo-2-phenyl-3,7-dihydro-2H-indole 1-oxide (11) react with primary aromatic amines to form products of mono- (5) and di-substitution (8), (9), and (12) and reduction (6). The reaction proceeds through several steps and a competition between nucleophilic attack and electron transfer (ET) may take place when amines characterized by a low oxidation potential, such as p-anisidine, are involved. Some mechanistic considerations are drawn based on ESR results and the E1/2 values of the oxidation and reduction potentials of the starting compounds, and the possibility is stressed that ET occurs at different stages of the reaction. It is conceivable that the disubstitution products (8) and (9) originate from the same intermediate (7), the formation of which remains a puzzle. The structures of compounds (5a), (6), (9a), and (12) have been determined by crystal X-ray analysis.