Syntheses of ent-Aquilanol A and ent-Aquilanol B via Retro-Cycloisomerization of (−)-Caryophyllene Oxide. Access to Medium-Sized Oxygenated Carbocyclic Scaffolds

The first syntheses of the enantiomers of naturally occurring aquilanols A and B, two unprecedented 7/10 bicyclic sesquiterpenoids, are presented. Key features are a retro-cycloisomerization event on (−)-caryophyllene oxide to formulate the 11-membered carbocycle and an intramolecular epoxide opening to construct the bicyclic skeleton. The latter provides evidence of the plausible biosynthesis of natural compounds, rendering our syntheses biomimetic. Selective access to other medium-sized carbocyclic oxygenated compounds was achieved, enhancing the structural diversity of the final products.