Concise Enantioselective Total Syntheses of Rearranged ent-Trachylobane Diterpenoids (-)-Wallichanols A and B.

Herein, we report the first enantioselective total syntheses of three rearranged ent-trachylobane diterpenoids, (-)-Wallichanol A (1), (-)-Wallichanol B (2), and (-)-Sanguinolane (3), using a 13, 17, and 14 step longest-linear sequences respectively, featuring 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.