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

• Synthesis of novel 1-amino-4-(ar)alkylaminoanthraquinones having a Br, CH2OH, CN, or CH3 in the 2-position of the scaffold.
• The target compounds were obtained by Ullmann condensation of bromaminic acid analogues with a variety of amines.
• Optimization of the conditions for the different reactions has been conducted.
• Comparison of the different bromaminic acid analogues in terms of chemical reactivity and reaction conditions is presented.
• The anthraquinone derivatives may be useful as new dyes or represent bioactive compounds for experimental pharmacology.

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.

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