Abstract
Though a pyrazole hydroazine vat dye (1) was formed by the direct cyclization of pyrazoleanthrone with 1-amino-2-bromoanthraquinone, the yield was as low as 10%. I, however, was obtained in 58% over-all yield in a two -step synthesis via cyclization of the intermediate, 2-(1'-amino-2-anthraquinonyl)-pyrazoleanthrone, in pyridine-methanol containing potassium hydroxide . 2-(2'-Aminophenyl)-pyrazoleanthrone was also readily cyclized into a pyrazole hydroazine compound . Similar reactions using 2-(3'-pyrazoleanthronyl)-pyrazoleanthrone and 3-anilino - pyrazoleanthrone, however, failed to take place. It is assumed that the cyclization reaction proceeds through a link formation between a -NH anion formed as shown below and a carbonium cation induced by the electron withdrawing effect of the carbonyl group in the pyrazoleanthrone ring.
