Thiourea-Catalyzed Asymmetric Michael Addition of Carbazolones to 2-Chloroacrylonitrile: Total Synthesis of 5,22-Dioxokopsane, Kopsinidine C, and Demethoxycarbonylkopsin.

A modified Takemoto catalyst enabled the asymmetric Michael addition of carbazolones to 2-chloroacrylonitrile to afford 3,3-disubstituted carbazolones with excellent enantioselectivity. This method was successfully applied to total syntheses of three Kopsia alkaloids which featured an unprecedented MnIII -mediated oxidative cyclization to create the caged ring system and a SmI2 -mediated reductive coupling as key steps.