Total Synthesis of Dehaloperophoramidine: Evolution of a Synthesis

This account describes our efforts toward developing a stereodivergent entry to perophoramidine and the communesin alkaloids. The original approach toward our simplified model substrates relied on a palladium-catalyzed carbopalladation–carbonylation of a tetrasubstituted olefin to install the vicinal all-carbon quaternary stereocenters present in the target molecules, the olefin's stereochemistry thus dictating the relative stereochemistry of the quaternary stereocenters. Although the carbonylation–carbopalladation sequence worked well for trisubstituted olefins, only premature esterification was observed when using tetrasubstituted alkene substrates. Our second approach made use of the latent symmetry embedded in our target molecules. A Diels–Alder reaction or SmI₂-mediated bis-alkylation of isoindigo was to be used to access the communesin and perophoramidine scaffolds, respectively. We found that due to unfavorable thermodynamics, it was not possible to reach the communesin scaffold. However, two new complexity-generating, cascade reactions were encountered en route to the synthesis of dehaloperophoramidine, resulting in a short and efficient synthesis.