Simultaneous Construction of Planar and Central Chiralities as Well as Unprecedented Axial Chirality on and around a Ferrocene Backbone

Simultaneous
generation of planar, central and axial chiralities
on and around a ferrocene backbone via a d-phenylglycinol-induced
intramolecular iminium cyclization was disclosed, which is rare and
differs from known methods. A series of chiral spiro­[cyclopentadienyl-1,2,3,3a-tetrahydropentalenyliron­(II)-1,2′-pyrrolidine]
derivatives were prepared acording to the new method, and their structures
were characterized unambiguously. The axial chirality caused by the
ferrocene backbone and the rigid spiral structure was verified by
NOESY and variable-temperature NMR experiments and single-crystal
XRD analyses. Mechanism for the stereoselective iminium cyclization
reaction was suggested, which was influenced by steric hindrance and
hydrogen bonding.