Synthesis of vinca alkaloids and related compounds. Part XCIII. Skeletal rearrangement of cyclovinblastine derivatives: Formation of a novel bisindole system

Article abstract of DOI:10.3987/com-98-s(h)25

Bisindole alkaloids of the vinblastine (VLB) type can be oxidized to give a Ψ-aspidosperma-aspidosperma type skeleton via 3'-7'-transannular cyclization. Acid catalysis triggers an aspidospermane→eburnane skeletal rearrangement of these cyclic derivatives, thus giving a novel bisindole system with a Ψ-eburnea-aspidosperma type skeleton. A previously unexplored aspect of this transformation is the observed retention or inversion at C(16') depending on the starting C(16') configuration. The present paper gives a detailed account of the synthetic aspect of this work together with preliminary NMR and CD results concerning the epimerization at C(16').