Syntheses of the Stemona Alkaloids (±)-Stenine, (±)-Neostenine, and (±)-13-Epineostenine Using a Stereodivergent Diels–Alder/Azido-Schmidt Reaction

A tandem Diels–Alder/azido-Schmidt reaction sequence provides rapid access to the core skeleton shared by several Stemona alkaloids including stenine, neostenine, tuberostemonine, and neotuberostemonine. The discovery and evolution of inter- and intramolecular variations of this process and their applications to total syntheses of (±)-stenine and (±)-neostenine are described. The stereochemical outcome of the reaction depends on both substrate type and reaction conditions, enabling the preparation of both (±)-stenine and (±)-neostenine from the same diene/dienophile combination.