Enantioselective Total Synthesis of Berkeleyone A and Preaustinoids.

Herein we report the first enantioselective total synthesis of 3,5-dimethylorsellinic acid-derived meroterpenoids (-)-berkeleyone A and its five congeners ((-)-preaustinoids A, A1, B, B1 and B2) in 12-15 steps, respectively, starting from commercially available 2,4,6-trihydroxybenzoic acid hydrate. Based upon the recognition of latent symmetry within D-ring, our convergent synthesis features two critical reactions: (1) a symmetry-breaking, diastereoselective dearomative alkylation to assemble the entire carbon core, and (2) a Sc(OTf) 3 -mediated sequential Krapcho dealkoxycarbonylation/carbonyl α- tert -alkylation to forge the intricate bicyclo[3.3.1]nonane framework. We also conducted our preliminary biomimetic investigations and uncovered a series of rearrangements (α-ketol, α-hydroxyl-β-diketone, etc ) responsible for the biomimetic diversification of (-)-berkeleyone A into its five preaustinoid congeners.