Divergent Asymmetric Total Synthesis of (+)-Vincadifformine, (−)-Quebrachamine, (+)-Aspidospermidine, (−)-Aspidospermine, (−)-Pyrifolidine, and Related Natural Products

A uniformly strategic
total synthesis of Aspidosperma alkaloids (+)-vincadifformine,
(−)-quebrachamine, (+)-aspidospermidine,
(−)-aspidospermine, (−)-pyrifolidine, and nine others
from efficiently constructed tricyclic ketone 13 is reported.
Highlights of these divergent and practical syntheses include (i)
stereoselective intermolecular [4 + 2] cycloaddition to establish
a C–E ring with one all-carbon quaternary stereocenter (C-5)
and two bridged contiguous cis-stereocenters (C-12
and C-19), (ii) a Pd/C-catalyzed hydrogenation/deprotection/amidation
cascade process to assemble the D ring, and (iii) Fischer indolization
to forge the A–B ring.