A highly efficient access to spiroketals, mono-unsaturated spiroketals, and furans: Hg(II)-catalyzed cyclization of alkyne diols and triols.

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.