Unusual products from oxidation of naphthalene diimides

Transforming the naphthalene diimide (NDI) core into unusual aromatic systems has large potential for applications in which current NDI-based systems show promise. Treatment of N,N-dialkylNDIs under mild oxidizing conditions with ruthenium(III) chloride and sodium periodate affords the corresponding 1,4-diones in good yield. Interestingly, while aliphatic substituents at the N-imide positions allowed oxidation to take place easily, the presence of neutral, electron-rich or electron-deficient phenyl groups retarded the oxidation process under these reaction conditions. The chemistry of the 1,4-dione is then explored through reduction and condensation reactions. In two examples, reaction of the 1,4-dione with diamines gives an unusual, ring-contracted product 20, which has a high quantum yield. Additionally, the 1,4-dione can be converted into larger heterocycles such as 21 and 22 featuring an isoquinoline core. The 1,4-diones and their products have been investigated by spectroscopy, cyclic voltammetry, theoretical studies, and X-ray crystallography. The results obtained demonstrate the potential of the 1,4-dione to serve as an invaluable precursor for NDI-based research.