Organocatalytic and Late-Stage CH-Functionalization Enabled Asymmetric Synthesis of Communesin F and Putative Communesins

Herein we report the total syntheses
of communesin F and putative
members of the communesin family of polycyclic bis-aminal alkaloids.
The successful strategy featured a novel organocatalytic reaction
between two oxindole subunits to cast, after extensive optimization,
the all-carbon vicinal quaternary stereocenters of the target molecule
with high enantiocontrol. The resulting bis-oxindole intermediate
further underwent a Ti­(OiPr)4-mediated dehydrative skeletal rearrangement to furnish the communesin
core structure. Consider the ready availability and low-cost of unsubstituted
isatin, and the inferior organocatalytic reaction employing a bromo-substituted
substrate, a Pd­(OAc)2-catalyzed and oxalamide-directed
aryl CH-alkenylation reaction was implemented to assemble the complete
skeletal backbone of the target molecule. Collectively, the synthetic
technologies disclosed herein constitute the first asymmetric organocatalytic
approach to the communesins, together with a highly effective late-stage
CH-functionalization in stark contrast to the bromoarene substrates
employed in all of the past synthetic work.