DERIVATIVES OF 14H-NAPHTHO[2,3-A]PHENOTHIAZINE-8,13-DIONE .3. SYNTHESES VIA BORIC-ACID COMPLEXES OF ALPHA-HYDROXY-ANTHRAQUINONES

The reaction of alpha-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-di ones proceeds with greater facility than with previously reported reac tions in the absence of boric acid, giving products in generally good yield and high purity. The use of ethanolic media, such as 2-methoxyet hanol, is more convenient than alternative methods involving, for exam ple phenol or Zn/HCl in the reaction system. Copyright (C) 1996 Elsevi er Science Ltd