Cationic cyclizations of (diene)iron tricarbonyl complexes with pendant alkenes and arenes

Stereospecific annulation reactions, which involve the intramolecular addition of olefinic and aromatic nucleophiles to in situ generated iron tricarbonyl-stabilized dienyl cations, are described. It is found that a simple unactivated olefinic double bond reacts to generate cyclohexane systems in high yield. On the other hand, reaction with aromatic moieties to form substituted tetralins proceeds only for activated aromatic rings; in those cases where less nucleophilic aromatics are used, a competing unproductive rearrangement of the diene–iron tricarbonyl complex occurs.