Preparation of 6-, 7-, and 9-substituted derivatives of 2-oxa-1,3,4,10-tetraazacyclopenta[b]fluoren-9-one

The preparation of a variety of derivatives of 2-oxa-1,3,4,10-tetraazacyclopenta[b] fluoren-9-one 1 is described. A series of substituted indan-1-ones were prepared and oxidized with N-bromosuccinimide and dimethyl sulfoxide to the corresponding ninhydrin derivatives. Cyclization of the ninhydrins with furazan-3,4-diamine yielded the target tetracycles. Appropiate choice of substituents in ninhydrins led to a preference for one regioisomer in the target tetracycles. This permitted the synthesis of a variety of 8-substituted heterocycles. In those instances where isomer formation was possible, structural assignments were confirmed by X-ray crystallography.