Asymmetric synthesis of the functionalized A/E bicyclic fragment of the C<sub>19</sub>-diterpenoid alkaloids

The C19-diterpenoid alkaloids belong to a class of natural products with significant biological activities. These molecules are structurally characterized by complex cage-like skeletons and dense functional substituents. The efficient preparation of the A/E aza-bridged ring system, which is ubiquitous in C19-diterpenoid alkaloids, would lay an important foundation for their total synthesis. This paper reports a new asymmetric synthesis of the functionalized A/E bicyclic fragment of the C19-diterpenoid alkaloids, featuring desymmetrization, diastereoselective allylaltion, aldol hydroxymethylation, and reductive amination as key steps.