Search

Hg(OTf)2-catalyzed cyclization of an alkynyl alcohol on a tetrahydropyran template gives the bispyranyl ketone arising from dehydrative cyclization and alkyne hydration, rather than the targeted fused pyran-oxepane product. The combination of stoichiometric Hg(OTf)2 and triethylsilane gives reductive cyclization, but affords the fused pyran-oxocane corresponding to an 8-endo-mode oxacyclization process. [ABSTRACT FROM AUTHOR]

Exploratory studies on the sequential exo-mode oxacyclizations of acyclic polyene precursors have provided a substantial substructure of brevenal, including the fused tricyclic polyether with stereochemical patterns consistent with the AB and BC ring fusions. The synthesis of acyclic substrates featured two variations of Cr(II)/Ni(II) couplings for preparing 1,1-disubstituted allylic alcohols. A sequence of iodine-promoted cycloetherification, base-promoted intramolecular conjugate addition, and mercury-promoted cycloetherification produced the tricyclic substructure. [ABSTRACT FROM AUTHOR]