Stereoselective Pinacol Coupling of Chiral Formylferrocene Using Divalent Samarium Triflate: Preparation of a New Chiral Bisferrocenyl Oxazoline Ligand and Its Application to Asymmetric Diels−Alder Reactions

The pinacol coupling reaction of planar chiral ortho-oxazoline-substituted formylferrocene was smoothly mediated by SmI2 or Sm(OTf)3 to give the (R,R) isomer selectivity (up to 76% diastereomeric excess). The combination of Yb(OTf)3 and the (R,R)-ferrocenyl diol was revealed to be a good catalyst for the asymmetric Diels−Alder reaction of 3-acyloxazolidinone with cyclopentadiene, and the endo adduct was produced in up to 80% enantiomeric excess.