A facile synthesis of bispyrroloquinone and bispyrroloiminoquinone ring system of marine alkaloids

Bispyrroloquinone and bispyrroloiminoquinone are two important polycyclic ring systems present in biologically active marine alkaloids such as Zyzzyanones, tsitsikammamines, and wakayin. A facile synthesis of these two ring systems starting from a 6-benzylamino indole-4,7-quinone or 6-benzylamino pyrroloiminoquinone is described here. This chemistry involves the construction of a pyrrole ring in a single step by treatment of the starting reagents with ethyl acetoacetate or phenylbutane-1,3-dione in the presence of ceric ammonium nitrate in MeOH/CH2Cl2 solvent.