Ring-chain isomerism and reactions of 2-(1-anthraquinonecarbonyl)-1,2,3,4-tetrahydrophthalazine

The ring isomer of the corresponding acyl derivative — 5,9-dioxo-17a-hydroxy-9,10,11,16-17,17a-hexahydro-5H-dibenzod,e,h]phthalazino2,3-a]cinnoline — was obtained by acylation of 1,2,3,4-tetrahydrophthalazine with anthraquinone-1-carboxylic acid chloride. Treatment of the product with thionyl chloride or hydrogen chloride gave the deeply colored 5,9-dioxo-9,10,11,16-tetrahydro-5H-dibenzod,e,h]phthalazino2,3-a]cinnolinium chloride. The possibility of charge transfer between the chloride anion and the phthalazinium cation is examined as a reason for the deep coloration. This compound very readily undergoes hydrolytic oxidative cleavage at the C-N bond to give 2-(2-formylbenzyl)-3,7-dioxo-2,3-dihydro-7H-dibenzod,e,h]cinnoline.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1411–1415, October, 1977.