Sodium hydroxide converts 2′-hydroxy-2-nitro-5′-methylchalcone (I) into 10-hydroxy-2-methyl-11H-[1]benzopyrano[3,2-b]indol-11-one (IIa), a derivative of a new heterocyclic system. Sulphur dioxide in methanol removes the hydroxy-group giving 2-methyl-11H[1]benzopyrano[3,2-b]indol-11-one (VIIIa), which is also obtained by the catalytic hydrogenolysis of the methyl ether (IIb). Ethyl phosphite converts 2′-nitro-6-methylflavone into (VIIIa) in a reaction which appears to involve nitrene insertion into a pyrone nucleus and which confirms the constitutions allocated to the new compounds. The 10-hydroxy-1,3-dimethyl (XIV) and the 10-hydroxy-3-methoxy-analogues (XIII), have also been prepared from appropriate chalcones, which are best prepared by the Friedel–Crafts method avoiding basic media. The new heterocyclic nucleus is relatively stable to moderate chemical attack (by acids, bases, oxidising agents, or reducing agents) and to mass spectral fragmentation. These features are attributed to a combination of charge separation phenomena and aromaticity.