Total Synthesis of Liangshanone.

The first total synthesis of a hexacyclic ent -kaurane diterpenoid alkaloid, liangshanone, has been completed. Its intricate cage-like framework was assembled through several key transformations including an oxidative dearomatization/Diels-Alder (OD/DA) cycloaddition sequence, a tandem alkene cleavage/ Mannich cyclization, a Robinson-type annulation, and an intramolecular aldol reaction. Notably, an organocatalytic enantio-selective α-hydroxymethylation process allowed the preparation of the enantioenriched tricycle 15a that should enable asymmetric access to the target natural product.