Flexible Approach to <i>Stemona</i> Alkaloids: Total Syntheses of (−)-Stemospironine and Three New Diastereoisomeric Analogs

Abstract

Total syntheses of (−)-stemospironine and three new diastereoisomeric analogs have been completed through a flexible strategy devised for <i>Stemona</i> alkaloids. The azabicycle <b>7</b> is the pivotal intermediate, from which the sequence splits according to each particular target. The most remarkable differential feature for stemospironine is the installation of the spiranic γ-lactone through an intramolecular Horner–Wadsworth–Emmons olefination. The configuration of the stereogenic center at C-11 was controlled by fine-tuning of the synthetic sequence