| Summary: | The stabilising effect of benzannulation on isoindenes formed in the course of sigmatropic shifts of (C<sub>5</sub>H<sub>5</sub>)Fe(CO)<sub>2</sub> or of organo-silyl groups, and on exocyclic allyl intermediates in the course of haptotropic shifts of organometallic fragments over polycyclic skeletons (fluorene, cyclopenta[<i>def</i>]phenanthrene, <i>syn</i> and <i>anti</i> dibenzpentalenes) is exemplified. This approach led to the development of the first organometallic molecular brake. Benzyne cycloadditions to anthracenes to form triptycenes also led to unexpected or multiple adducts that were characterised by X-ray crystallography. Synthetic routes to the previously elusive benz[<i>cd</i>]azulene system are presented. Finally, the complete mechanism of the stepwise assembly of dispiro- and diindenyltetracenes from fluorenylallenes is presented, whereby every intermediate has been unambiguously structurally characterised.
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