Construction of a Bicyclo[2.2.2]octene Skeleton via a Visible-Light-Mediated Radical Cascade Reaction of Amino Acid Derivatives with N-(2-Phenyl)benzoyl Groups

Bridged polycyclic ring systems constitute the core structures of numerous natural products and biologically active molecules. We found that simple biphenyl substrates derived from amino acids participate in a radical cascade reaction under visible light irradiation in the presence of [Ir{dF(CF₃)ppy}₂(dtbpy)]PF₆ to enable the direct construction of bicyclo[2.2.2]octene structures. Isotopic labeling experiments suggested that intramolecular hydrogen atom transfer is involved in the cascade processes.

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 congeners.

Total Synthesis of (±)-Leonuketal

Leonuketal is an 8,9-seco-labdane terpenoid with a unique tetracyclic structure, owing to a diversity-generating biosynthetic C-C bond cleavage event. The first total synthesis of leonuketal is reported, featuring a Ti(III)-mediated reductive cyclization of an epoxy nitrile ether, an unusual ring-opening alkyne formation as part of an auxiliary ring strategy, and the previously undescribed Au(I)-catalyzed cyclization of a β-keto(enol)lactone to assemble the core spiroketal motif.

Noncanonical Cation-π Cyclizations of Alkylidene β-Ketoesters: Synthesis of Spiro-fused and Bridged Bicyclic Ring Systems

Three cation-π cyclization cascades initiated at alkylidene β-ketoesters bearing pendent alkenes are described. Depending upon the alkene substitution pattern and the reaction conditions employed, it is possible to achieve selective synthesis of the three different types of products, including 1-halo-3-carbomethoxycyclohexanes, spiro-fused tricyclic systems, and [4.3.1] bridged bicyclic ring systems. All three reactions begin with 6- endo addition of an olefin to the alkylidene β-ketoester electrophile, followed by one of three different cation capture events.

Total Synthesis of (±)-Berkeleyone A

A 13-step total synthesis of the fungal meroterpenoid berkeleyone A is reported. The molecular skeleton is formed using the first examples of two critical construction reactions: (1) an epoxide-initiated, β-ketoester-terminated polycyclization, and (2) an isomerization-cyclization cascade to generate the remaining bicyclo[3.3.1]nonane framework. The resulting 6-step synthesis of the carbocyclic core of the berkeleyone natural products has been used to access protoaustinoid A and berkeleyone A, and will aid future biosynthetic investigations into the origin of related natural products.

Annulative Methods Enable a Total Synthesis of the Complex Meroterpene Berkeleyone A

Synthetic pathways to complex meroterpenes derived from 3,5-dimethylorsellinic acid (DMOA) and farnesyl pyrophosphate have not been reported despite heavy biosynthetic and medicinal interest. Herein we report the first total synthesis of berkeleyone A, a potential gateway compound to a plethora of fungal-derived meroterpenes, in 13 steps. In addition, we have further developed a novel annulation reaction for the synthesis of hydroxylated 1,3-cyclohexadiones in a single step.