The furan approach to oxacycles: synthesis of medium-size 2,3-disubstituted oxacycles

Furan Derivatives and Polyketides from the Fungus Irpex lacteus

Eight new furan derivatives, irpexins A‒H (1‒8), two new polyketides, irpexins I and J (9 and 10), together with nine known compounds were isolated from the fermentation of Irpex lacteus. The structures and absolute configurations were elucidated on the basis of extensive spectroscopic methods and Mosher ester reaction. All compounds shows no cytotoxicity to human MCF-7 and Hela cancer cell lines at the concentration of 10 μM.

Synthesis of α,α'-trans-oxepanes through an organocatalytic oxa-conjugate addition reaction

Oxepanes are found in a wide range of natural products; however, they are challenging synthetic targets due to enthalpic and entropic barriers. Organocatalytic oxa-conjugate addition reactions promoted by the gem-disubstituent (Thorpe–Ingold) effect stereoselectively provided α,α′-trans-oxepanes. In addition, the potential of an organocatalytic tandem oxa-conjugate addition/α-oxidation was demonstrated in a rapid generation of molecular complexity. These organocatalytic oxa-conjugate addition reactions would provide powerful tools for the synthesis of natural products that contain highly functionalized oxepanes.

(3aRS,7aSR)-7a-Methoxy-2-oxo-2,3,3a,4,5,6,7,7a-octahydro-1-benzofuran-4,4-dicarbonitrile

The racemic title compound, C₁₁H₁₂N₂O₃, contains a [4.3.0]bicyclic unit in which the shared C—C bond adopts a cis configuration. The five- and six-membered rings are in twisted envelope (with the bridgehead C atom bearing the methoxy substituent as the flap) and distorted chair conformations, respectively. In the crystal, the mol­ecules are linked via weak C—H⋯O iteractions, forming ladder-like chains along [010].

Synthesis and complete assignment of the 1H and 13C NMR spectra of 6-substituted and 2,6-disubstituted pyridazin-3(2H)-ones

Several pyridazin-3(2H)-one derivatives were synthesized starting from alkyl furans using oxidation with singlet oxygen to give 4-methoxy or 4-hydroxybutenolides, key intermediates of the synthetic strategy followed. For all pyridazinones reported, a complete assignment of the (1)H and (13)C NMR spectra using one- and two-dimensional NMR spectroscopic methods, which included NOE, DEPT, COSY, HSQC and HMBC experiments, was accomplished. Correlations between the chemical shifts of the heterocyclic ring atoms and substituents at N-2 and C-6 were analyzed.

Stereoselective 6-exo radical cyclization using cis-vinyl sulfoxide: practical total synthesis of CTX3C

Ciguatoxins, the principal causative toxins of ciguatera seafood poisoning, are large ladder-like polycyclic ethers. We report a highly stereoselective 6-exo radical cyclization/ring-closing olefin metathesis sequence to construct the syn/trans-fused polyether system. The new method was applied to the practical synthesis of ciguatoxin CTX3C.