Reinvestigation of the Synthesis of Hydroxy‐Functionalized Diazapentacene: Unexpected Formation of a Phenoxazinone

In 1982, Buckley et al. reported on the hydroxy‐functionalized derivative of 6,13‐diazapentacene (DAP), namely 5,12‐dihydroxo‐6,13‐diazapentacene. In an attempt to reproduce the synthetic procedure, 1 H NMR and 13 C{ 1 H} NMR spectroscopic data revealed the formation of a constitutional isomer of the supposed compound. A single‐crystal X‐ray structure determination revealed that the actual structure of the dark‐violet product was 6‐amino‐5 H ‐dibenzo[ a , h ]phenoxazin‐5‐one ( 2 ), a benzo[ a ]phenoxazine derivative. These kinds of compounds are, along with a wide range of pharmacological applications, known for their specific fluorescent properties, which were analyzed for compound 2 . Furthermore, it was shown that 2 can be utilized as reagent for the synthesis of other benzo[ a ]phenoxazine derivatives, herein 6‐(dimethylamino)‐5 H ‐dibenzo[ a , h ]phenoxazin‐5‐one ( 3 ).