Divergent Total Synthesis of 17-nor-Excelsinidine and Geissoschizoline.

Using the key intermediate previously established in our group's synthetic investigations of monoterpenoid indole alkaloids, concise and efficient total synthetic routes toward the 17-nor-excelsinidine and geissoschizoline were developed. The synthesis of 17-nor-excelsinidine relied on oxidative cyclization and intramolecular N-alkylation as the pivotal transformations. Following this strategy, a concise total synthesis of this alkaloid was accomplished. For geissoschizoline, we developed a biomimetic synthetic route featuring a cascade reaction sequence: Mn(OAc)3-mediated oxidative cyclization and skeletal reorganization. The target molecule was secured in a seven-step longest linear sequence, alongside a formal synthesis of dehydrogeissoschizoline.