Derivatives of 14H-naphtho[2,3-a]phenothiazine-8,13-dione—III. Syntheses via boric acid complexes of α-hydroxy-anthraquinones

Abstract

The reaction of α-hydroxy (and amino) derivatives of anthraquinone with 2-aminobenzenethiol in the presence of boric acid is evaluated. The formation of the resulting 14H-naphtho[2,3-a]phenothiazine-8,13-diones proceeds with greater facility than with previously reported reactions in the absence of boric acid, giving products in generally good yield and high purity. The use of ethanolic media, such as 2-methoxyethanol, is more convenient than alternative methods involving, for example phenol or Zn HCl in the reaction system.