Evolution of a Unified, Stereodivergent Approach to the Synthesis of Communesin F and Perophoramidine

Expedient synthetic approaches to
the highly functionalized polycyclic
alkaloids communesin F and perophoramidine are described using a unified
approach featuring a key decarboxylative allylic alkylation to access
a crucial and highly congested 3,3-disubstituted oxindole. Described
are two distinct, stereoselective alkylations that produce structures
in divergent diastereomeric series possessing the critical vicinal
all-carbon quaternary centers needed for each synthesis. Synthetic
studies toward these challenging core structures have revealed a number
of unanticipated modes of reactivity inherent to these complex alkaloid
scaffolds. Additionally, several novel and interesting intermediates
en route to the target natural products, such as an intriguing propellane
hexacyclic oxindole encountered in the communesin F sequence, are
disclosed. Indeed, such unanticipated structures may prove to be convenient
strategic intermediates in future syntheses.