Reduction Product and Leuco-form of Flavanthrone

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Abstract
By reducing flavanthrone (II), 8,16-diazapyranthrene (V) (denoted as flavanthrene) was obtained. On the other hand, leucoflavanthrone dibenzoate was also prepared. Since these two substanses give nearly identical absorption spectra, the leucobenzoate is considered to have the VI formula (5,13-dibenzoyloxy-8,16-diazapyranthrene) and to belong to the same conjugated system as flavanthrene. Consequently, it may be considered that the leuco-form of flavanthrone corresponds to the IV formula (5,13-dihydroxy-8,16-diazapyranthrene) in which two carbonyl groups are reduced, but not the III formula (8-hydro-13-hydroxy-5-oxo-8,16-diazapyranthrene) previously presented. In addition, the leucobenzoate can also be synthesized by boiling the quinone with zinc dust and benzoyl chloride in o-dichlorobenzene containing pyridine. This method, devised by the author, is easy to perform and gives a good yield.