Concise Enantioselective Total Syntheses of Rearranged ent-trachylobane diterpenoids: (-)-Wallichanol A, (-)-Wallichanol B and (-)-Sanguinolane

Herein, we report the first, 13-step enantioselective total syntheses of the rearranged ent-trachylobane diterpenoids wallichanol A, sanguinolane, and wallichanol B, achieved via a novel intramolecular [2+2] cycloaddition to construct the unique pentacyclic framework containing an unprecedented tricyclo[3.3.1.02,7]nonane motif. Other key steps in the synthetic route include a highly challenging, selective alkene reduction via hydrogen atom transfer (HAT), leveraging the thermodynamic preference for a tertiary carbon-centered radical; a Robinson-type annulation to construct the tricyclic terpenoid building block; and applying aerobic oxidation at two distinct points to form α-hydroxy ketones, facilitating the enantioselective syntheses of these diterpenoids.