Reduction of 1-Hydroxyimidazole Derivatives Containing 4-Nitrophenyl Moiety

The reduction of 1-hydroxydimiazole derivatives containing a nitrophenyl substituent was studied. Reduction of either 1-hydroxy-4,5-dimethyl-2-(4-nitrophenyl)imidazole or 1-hydroxy-4,5-dimethyl-2-[2-(4-nitrophenyl)ethenyl]imidazole with sodium dithionite promptly resulted in products of complete reduction, i.e., aniline-containing imidazoles with no additional substituents at the nitrogen atoms in positions 1 and 3 of the heterocycle. Two synthetic routes to 5-acetylimidazoles containing 2-(4-aminophenyl) or 2-[2-(4-aminophenyl)ethenyl] moieties with no substituents at the nitrogen atoms of the heterocycle were proposed. These compounds were obtained as by-products in the reduction reactions of starting 5-acetyl-1-hydroxyimidazole derivatives with either sodium dithionite in the presence of base in THF–H2O media or zinc in glacial acetic acid. Otherwise, these aminophenyl-containing 5-acetylimidazoles were synthesized by a two-step procedure including selective reduction of the hydroxyl group in position 1 of nitrophenyl-substituted imidazoles followed by the reduction of the nitro group of the substituent with sodium dithionite. The possibility of the acquisition of 5-acetyl-1-hydroxyimidazole derivatives containing a primary amino group in the aryl substituent was also demonstrated for the first time.