Lewis Acid Mediated Coupling of Silyloxyallylsilanes and Ortholactones: A Convergent, Fragment-Coupling Approach to Functionalized Spiroketals

A convergent, fragment-based coupling approach to the formation of spiroketals has been developed. This approach combines the spiroketal forming step with a fragment coupling utilizing ortholactones as double electrophiles with silyloxyallylsilanes. We also discoved a rapid and regioselective isomerization of the exo-cyclic sprioketals to their endo-cyclic forms.