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(O^<i>i</i>Pr)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