An enantiodivergent protocol from R-(−)-carvone: synthesis of dihydroagarofuran sesquiterpenoid 1-deacetoxy-ent-orbiculin A

Total Synthesis of (-)-Sigillin A: A Polychlorinated and Polyoxygenated Natural Product

The total synthesis of (-)-sigillin A, a highly chlorinated and oxygenated octahydroisocoumarin, is described herein. A hexahydroisocoumarin skeleton was constructed from (R)-4-(trichloromethyl)oxetan-2-one in seven steps. Its unique manganese oxidation provided an enone as the key intermediate of sigillin A. Stereoselective installation of two hydroxy groups and formation of gem-dichloroalkene from the corresponding ketone led to the total synthesis of (-)-sigillin A in a total of 16 steps.

Tripterfordins A-O, Dihydro-β-agarofuran Sesquiterpenoids from the Leaves of Tripterygium wilfordii

Fifteen new dihydro-β-agarofuran-type sesquiterpenoids, tripterfordins A-O, were obtained from the aqueous EtOH extracts of the leaves of Tripterygium wilfordii. These constituted a class of highly oxygenated tricyclic sesquiterpenoid polyesters with a cinnamoyloxy group at C-1. The assignments of their structures were conducted via extensive analyses of the spectroscopic data and comparison of experimental and calculated ECD data. The absolute configurations of compounds 1, 4, 9, and 10 were established via single-crystal X-ray diffraction data. Additionally, compounds 1, 4, 9, 10, and 13 exhibited pronounced inhibitory effects on nitric oxide production in RAW 264.7 murine macrophages stimulated by lipopolysaccharide with IC₅₀ values ranging from 11.9 to 31.0 μM.

Intramolecular [2 + 2] Cycloadditions of Alkyl(phenylthio)ketenes: Total Synthesis of (+)-Sphaerodiol

Asymmetric total synthesis of (+)-sphaerodiol (2) has been achieved. A key step is an intramolecular [2 + 2] cycloaddition of alkyl(phenylthio)ketene for rapid assembly of the decalin ring.

Construction of the septahydroxylated ABC-ring system of dihydro-β-agarofurans: application of 6-exo-dig radical cyclization

A synthetic route to the septahydroxylated ABC-ring system of dihydro-β-agarofurans was established. The B-ring was formed by a base-promoted diastereoselective Diels-Alder reaction between 3-hydroxy-2-pyrone and a d-glyceraldehyde-derived dienophile, while the C-ring was cyclized by PhSeCl-mediated etherification. The remaining A-ring was constructed via a 6-exo-dig radical reaction. Selective transformations gave rise to the ABC-ring system 1 with nine contiguous stereocenters. The thus obtained 1 corresponded to the enantiomer of the densely oxygenated core structure of dihydro-β-agarofurans.