Highly enantioselective hetero Diels–Alder reactions of N-sulfinyl dienophiles promoted by copper(II)- and zinc(II)-chiral bis(oxazoline) complexes

Abstract

Hetero Diels–Alder reactions of 1,3-cyclohexadiene with N-sulfinyl dienophiles 1a or 1b, promoted by Cu(II)- or Zn(II)-chiral bis(oxazoline) complexes, afforded endo adducts in high yields (up to 85%) and enantiomeric excess (e.e. of up to >98%) under stoichiometric conditions. With 10 mol% loading of the Zn(II) catalyst up to 75% e.e. was obtained for the endo adduct ( endo: exo=10:1, total yield 68%).