ENANTIOSELECTIVE SYNTHESIS OF (+)-INDOLIZIDINE, (+)-LABURNINE AND (+)-ELAEOKANINES A AND C USING THE DIELS-ALDER REACTION OF ALPHA-(2-EXO-HYDROXY-10-BORNYLSULFINYL)MALEIMIDE

The Diels-Alder adduct 5 derived from the N-butynylmaleimide sand cyclopentadiene has been transformed into the tetracyclic lactams 12 and 19 via 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 A3 and (+)-elaeokanine C4.