Synthetic study of perophoramidine: construction of pentacyclic core structure via SmI2-mediated reductive cyclization

An intramolecular SmI2-mediated reductive cyclization of carbodiimides and unsaturated lactams was applied to functionalized substrates bearing tetrasubstituted olefins. The reaction afforded arylated spiro-2-iminoindolines in high yield. Although the stereochemistry of the product was different from the desired one, the optimized palladium-catalyzed aryl amidination realized the isomerization and C–N bond formation in a single step and resulted in efficient construction of pentacyclic core of perophoramidine synthetically equivalent to the Rainierʹs intermediate.