Protecting Group-Free Total Synthesis of (−)-Lannotinidine B

Abstract

The first total synthesis of (−)-lannotinidine B, a unique tetracyclic constitutent of <i>Lycopodium annotinum</i>, has been accomplished in 10 steps with 23% overall yield. The completed short and efficient synthesis is characterized with three highly chemo- and/or stereoselective reductive-amination steps to furnish the desired <i>trans</i>-fused 6/6 bicycle and the aza seven-membered ring system, and a direct intramolecular acyloin condensation to deliver the cyclopentanone moiety, as well as successful application of a protecting group-free strategy and an optimal redox order