Hg(II) salts are identified as highly efficient catalysts for the versatile construction of spiroketals from alkyne diols in aqueous conditions. Monounsaturated spiroketals and furans were accessed with equal ease when propargylic triols (or propargylic diols) were subjected to similar conditions. Even the semiprotected alkyne diols gave the corresponding spiroketals with the same ease in a cascade manner. The reactions are instant and high yielding at ambient temperatures. Regioselectivity issues are well addressed.

The steroidal natural product hippuristanol targets eukaryotic translation initiation factor (eIF)4A which plays a pivotal role in translation in eukaryotic cells. Now an efficient synthesis of hippuristanol from 11-ketotigogenin is reported. The synthesis features a rapid construction of a spiroketal unit via Hg(OTf)(2)-catalyzed oxidation/spiroketalization of the 3-alkyn-1,7-diol motif.

A stereoselective total synthesis of (+)-cassaine (1) via an anionic polycyclization methodology is described. Commercially available (+)-carvone (5), the only chiral source, was used to fix the entire stereochemistry of the natural product. Anionic polycyclization of a new substituted 2-(methoxycarbonyl)cyclohex-2-en-1-one (4) with known 1-phenylysulfinyl-3-penten-2-one (3) provided the versatile tricycle (2) with requisite stereochemistry. A sequence of functional group manipulations of tricycle (2) furnished the natural product 1.