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