Yoshitsugu Arai, Tsutomu Masuda and Yukio Masaki
1-[2-(p-Tolylsulfinyl)]pyrrolyl α,β-unsaturated enones served as efficient dienophiles in the Diels–Alder reaction, where the use of aluminium chloride or a lanthanide triflate effected the cycloaddition with cyclopentadiene, affording the endo adduct with high diastereoselectivity. In particular, for the sulfinyl dienophile, the chiral auxiliary (i.e. the sulfinyl pyrrole) was recovered after use without any loss of optical purity.