Synthesis of Enantiopure Planar Chiral Bisferrocenes Bearing Sulfur or Nitrogen Substituents

A new procedure for the preparation of enantiopure planar chiral bisferrocenes bearing
potentially metal-coordinating sulfur or nitrogen substituents is reported. The diastereoselective ortho-lithiation of enantiopure sulfinyl- or oxazolidinylferrocenes followed by treatment
with nonenolizable esters leads in a one-pot operation to the corresponding bisferrocenyl
carbinols. Due to the presence of a strong hydrogen bond between the hydroxyl group and
one of the sulfinyl moieties, the pyrolysis of the bis(sulfinyl)bisferrocene 3a in toluene at
110 °C takes place by selective removal of the non-hydrogen-bonded sulfoxide to afford in
good yield a tetraferrocene disulfide derivative. Interesting structural information for these
novel bi- and tetraferrocenes, deduced by NMR and X-ray crystallography, is also discussed.