Acid-Catalyzed Formal Cycloaddition of α,β-Unsaturated Carbonyls with Epoxides: Dioxepines or Acetals?

It has been recently reported that the reaction of α,β-unsaturated carbonyl derivatives with epoxides in the presence of a homogeneous acid catalyst readily delivers the corresponding dioxepines via formal (4 + 3) cycloaddition. We report herein that the same apparent reactivity can be triggered via heterogeneous catalysis. Characterization of products by means of NMR correlation experiments and DFT modeling revealed, however, that products are the acetals of the unsaturated reagent rather than the desired heterocycles.