Total Synthesis of ent-Ascospiroketal B

Biomimetic total synthesis of plakortone Q via acid-mediated tandem cyclization

Plakortone Q and plakdiepoxide are natural polyketides isolated from the marine sponge Plakortis simplex. Bicyclo[3.3.0]furanolactone compounds, including plakortone Q, are expected to exhibit a wide range of pharmacological activities. Therefore, developing a simple and versatile synthetic method to produce these compounds is an important research goal. We have achieved the first total synthesis of plakortone Q and plakdiepoxide through an efficient protecting-group-free strategy. The key transformation was an acid-mediated tandem 5-endo-tet/5-endo-tet cyclization of vicinal diepoxide to build the tetrahydrofuran-γ-lactone motif.

Total Synthesis of Ascospiroketal B

An enantioselective total synthesis of the marine tricyclic polyketide ascospiroketal B, previously isolated from the marine-derived fungus Ascochyta salicorniae, was accomplished in 21 steps by using an improved route. The intriguing 5,5-spiroketal-cis-fused-γ-lactone core was constructed through rearrangement of an epoxide, in conjunction with an acid-mediated spiroketalization.

Dual Lewis Acid/Photoredox-Catalyzed Addition of Ketyl Radicals to Vinylogous Carbonates in the Synthesis of 2,6-Dioxabicyclo[3.3.0]octan-3-ones

A combined Lewis acid/photoredox catalyst system enabled the intramolecular umpolung addition of ketyl radicals to vinylogous carbonates in the synthesis of 2,6-dioxabicyclo[3.3.0]octan-3-ones. This reaction proceeded on a variety of aromatic ketones to provide THF rings in good yield (up to 95%). Although diastereoselectivity was found to be modest (1.4-5:1) for the C-C bond forming reaction, the minor diastereomers were converted to 2,6-dioxabicyclo[3.3.0]octan-3-ones by an efficient Lewis acid-mediated epimerization cascade in up to 90% yield.