Asymmetric Total Synthesis of Sarpagine and Koumine Alkaloids.

We report here a concise, collective, and asymmetric total synthesis of sarpagine alkaloids and biogenetically related koumine alkaloids, which structurally feature a rigid cage scaffold, with L‐tryptophan as the starting material. Two key bridged skeleton‐forming reactions, namely tandem sequential oxidative cyclopropanol ring‐opening cyclization and ketone α‐allenylation, ensure concurrent assembly of the caged sarpagine scaffold and installation of requisite derivative handles. With a common caged intermediate as the branch point, by taking advantage of ketone and allene groups therein, total synthesis of five sarpagine alkaloids (affinisine, normacusine B, trinervine, Na‐methyl‐16‐epipericyclivine, and vellosimine) with various substituents and three koumine alkaloids (koumine, koumimine, and N‐demethylkoumine) with more complex cage scaffolds has been accomplished. [ABSTRACT FROM AUTHOR]