Synthesis of 10‐Aryl‐10H‐naphtho[1,8a,8‐fg]indazol‐7‐ones

3‐Hydroxy‐2‐1‐(arylhydrazono)ethyl]‐1H‐phenalen‐1‐ones 3 , obtained from 2‐acetyl‐3‐hydroxy‐1H‐phenalen‐1‐one ( 1 ) and arylhydrazines 2 , cyclize under acidic conditions to 8‐methyl‐10‐aryl‐10H‐naphtho‐1,8a,8‐fg]indazol‐7‐ones 4 . Indazoles 4 are also obtained from 2‐acetyl‐3‐hydroxy‐1H‐phenalen‐1‐one ( 1 ) and arylhydrazines 2 in a one‐pot reaction. 2‐Acetyl‐3‐azido‐1H‐phenalen‐1‐one ( 6 ) does not give 8‐methyl‐9‐arylamino‐9H‐naphtho1,8a,8‐fg]indazol‐7‐ones via azide decomposition but gives again by nucleophilic replacement of the azide moiety in 6 the indazole 4 .