Pd(II)-catalyzed spiroketalization of ketoallylic diols.

A high-yielding stereoselective method for forming spiroketals from simple ketoallylic diols is reported. Employing catalytic [PdCl2(MeCN)2] in THF at 0 °C, these dehydrative cyclization reactions require only mild conditions to produce vinyl-substituted spiroketals in high yields after brief reaction times with water as the only byproduct. Using this method, the stereochemical information embedded at the nucleophile is transmitted "down-the-chain" and efficiently sets the stereochemistry at both the anomeric carbon atom and the newly formed allylic stereocenter.

Au-catalyzed cyclization of monopropargylic triols: an expedient synthesis of monounsaturated spiroketals.

The gold-catalyzed cyclization of monopropargylic triols to form olefin-containing spiroketals is reported. The reactions are rapid and high yielding when 2 mol % of the catalyst generated in situ from Au[P(t-Bu)(2)(o-biphenyl)]Cl and AgOTf is employed in THF at 0 degrees C. A range of differentially substituted triols leading to substituted 5- and 6-membered ring spiroketals were prepared and function well in the reaction.