An iodoetherification-dehydroiodination strategy for the synthesis of complex spiroketals from dihydroxyalkene precursors.

Dihydroxyalkenes or their monoprotected alcohol derivatives are transformed to 5,5- and 5,6-spiroketals through a sequence involving an initial iodocyclization, followed by a silver triflate mediated spiroketalization step on the derived hydroxy-iodoether.