Rearrangements and Migrations along the Ferrocene Periphery: On the Way to Planar-Chiral and (Multi)Substitution Patterns

The functionalization of ferrocenes via intramolecular rearrangements is summarized. Focus will be directed on anionic, cationic and thermal/photo-induced processes that enable the migration of functional groups along the periphery of the ferrocene's cyclopentadienyl rings. Anionic processes include halogen dance reactions and Fries rearrangements. The metalation procedures are discussed, which are essential for a regio- and stereoselective proceeding. Computational studies and electrochemical data are included to discuss stereoselective processes and reactivity differences. Positioning of a positive charge in close proximity to the ferrocenyl backbone induces Pinacol, Beckmann, and remote Fries rearrangements. Activation of an alkynyl functionality facilitates alkyne/vinylidene changes. Thermal rearrangements do not require an additional charge and are induced by N₂ elimination, followed by nitrene/carbene formation via Curtius and Wolff rearrangements, respectively. The latter was exemplarily used for the ring contraction of [4]- into [3]ferrocenophanes.