Ullmann reactions of 1-amino-4-bromoanthraquinones bearing various 2-substituents furnishing novel dyes

Novel 1-amino-4-(ar)alkylaminoanthraquinone derivatives bearing different substituents (Br, CH₂OH, CN, or CH₃) at the 2-position of the anthraquinone scaffold were synthesized by copper-catalyzed Ullmann condensation. The 2-substituted 1-amino-4-bromoanthraquinone derivatives (bromaminic acid analogues) were reacted with a variety of alkyl-, aryl-, and aralkylamines. Different reaction conditions were applied depending on the physical state of the amine and the nature of the substituent at the 2-position of the anthraquinone scaffold. A solvent-free synthetic procedure was developed for reactions with liquid amines. Condensation with solid amines required the addition of a solvent, and reaction conditions had to be optimized for each of the anthraquinone derivatives. Our results emphasize that copper-catalyzed reactions are highly variable depending on the molecules and anions present in the medium, since different reaction mechanisms apply. The synthesized anthraquinone derivatives may be useful as new dyes, or may show biological activity and could be employed as tool compounds in experimental pharmacology.