2. 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, 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 congener.