Recoverable Chiral Sulfoxide: Asymmetric Diels–Alder Reaction Using Optically Active 1-(2-p-Tolylsulfinyl)pyrrolyl α,β-Unsaturated Ketones as a Dienophile

The Diels–Alder reaction of chiral cinnamoyl- and crotonyl(2-p-tolylsulfinyl)pyrrole with cyclopentadiene in the presence of AlCl3 or Yb(OTf)3 proceeded smoothly to give the corresponding endo adducts in excellent yield with high diastereoselectivity, ranging from 92 to 99% d.e. The chiral auxiliary, 2-pyrrolesulfoxide was efficiently recovered after alcoholysis of the adduct without loss of optical purity.