Annulenoannulenes

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Abstract
Annulenoannulenes formally consist of two annulenes fused together. Hitherto, almost all the known representatives of this class of compounds were the strongly dehydrogenated forms, containing a few triple bonds and several cumulated double bonds. Besides ortho‐annelated dehydroannulenoannulenes also such compounds containing bridges made up of two or four carbon atoms (“acetylene‐cumulene” annulenoannulenes) were obtained by multistep syntheses. Most dehydroannulenoannulenes are stable and form colored crystals. In addition to dehydro[4n+2]annuleno[4n+2] annulenes with 14‐, 18‐, and 22‐membered individual rings, two dehydro[4n]annuleno[4n+2]annulenes with 16‐ and 14‐, and 16‐ and 18‐membered rings have also been synthesized. Planar combinations of two [4n]‐rings of this type and size are not known.—The dehydrogentated[14]annuleno[14]annulene containing a bridge of two carbon atoms has been studied in detail; however, the problem of the induction of a diamagnetic ring current in compounds of this type has still not been completely clarified.