(-)-Mimamine (2), the first pentacyclic proaporphine alkaloid, has been found in Egyptian Roemeria hybrida and R. dodecandra (Papaveraceae); The title compound has been shown to undergo conjugate addition to a variety of α,β-unsaturated ketones to afford β-seleno boron enolates which are convertable to unsaturated ketols upon treatment with aldehydes and subsequent oxidative elimination.