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.