SYNTHESIS OF VINCA ALKALOIDS AND RELATED COMPOUNDS.PART XCIII.~1 SKELETAL REARRANGEMENT OF CYCLOVINBLASTINE DERIVATIVES:FORMATION OF A NOVEL BISINDOLE SYSTEM

摘要

Bisindole alkaloids of the vinblastion (VLB) type can be oxidized to give a #PSA#-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 #PSA#-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 gogether with preliminary NMR and CD results concerning the epimerization at C(16~').