Enantioselective synthesis of (+)-indolizidine, (+)-laburnine and (+)-elaeokanines A and C using the Diels–Alder reaction of α-(2-exo-hydroxy-10-bornylsulfinyl)maleimide

Abstract

The Diels–Alder adduct 5 derived from the N-butynylmaleimide 6 and cyclopentadiene has been transformed into the tetracyclic lactams 12 and 19via a common precursor 9. The lactams 12 and 19 have been converted into (+)-indolizidine 1 and (+)-laburnine 2, respectively, via retro-Diels–Alder reaction. Similar methodology has been successfully applied to the synthesis of (+)-elaeokanine A 3 and (+)-elaeokanine C 4.