Total syntheses of (+)-geissoschizine, (±)-geissoschizine, and (±)-(Z)-isositsirikine. Stereocontrolled synthesis of exocyclic double bonds by stereospecific iminium ion-vinylsilane cyclizations

Article abstract of DOI:10.1021/ja00183a046

(+)-Geissoschizine (1) was prepared in an efficient and stereocontrolled fashion in 11 steps and 7.5% overall yield from (S)-tryptophanamide (20). Key steps are the stereoselective 1,4-addition of cuprate 13a to tetracyclic intermediate 8, which establish