Studies on Heterocyclic Colouring Matters Part III: 7a,14a-diaza-7,7a,14,14a-tetrahydroquino[2,3-b]acridine-7,14-diones (5,7a,12,14a-tetraaza-7,7a,14,14a-tetrahydropentacene-7,14-diones)

2-Aminopyridines react with diethyl 2,5-dioxo-cyclohexane-1,4-dicarboxylate (diethyl succinylsuccinate) to give 7a,14a-diaza-6,7,7a,13,14,14a-hexahydroquino-2,3-b] acridine-7,14-diones (5,7a,1,14a-tetraaza-6,7,7a,13,14,14a-hexahydropentacene-7,14-diones), which are aromatized to the title compounds. Oxidation of these with a mixture of sulfuric and nitric acids results in the formation of their respective 6,13-quinones, also obtained directly from 2-aminopyridines and diethyl 2,5-dichloro-1,4-benzoquinone-3,6-dicarboxylate. The chromophore of the title compounds is compared with that of quinacridones.