Unified Strategy to Monoterpene Indole Alkaloids: Total Syntheses of (±)-Goniomitine, (±)-1,2-Dehydroaspidospermidine, (±)-Aspidospermidine, (±)-Vincadifformine, and (±)-Kopsihainanine A

Total
syntheses of (±)-goniomitine, (±)-1,2-dehydroaspidospermidine,
(±)-aspidospermidine, (±)-vincadifformine, and (±)-kopsihainanine
A were achieved featuring two common key steps: (1) a palladium-catalyzed
decarboxylative vinylation that provides quick access to cyclopentene
intermediates containing all of the carbons present in the natural
products and (2) an integrated oxidation/reduction/cyclization (iORC) sequence for skeletal reorganization that
converts the cyclopentenes to the pentacyclic structures of the natural
products. By incorporation of a geometric constraint to iORC substrates, both the chemoselectivity (C7 vs N1 cyclization)
and the stereoselectivity (trans- vs cis-fused ring system) of the
cyclization process can be controlled.