Remote Chiral Induction in Vinyl Sulfonium Salt‐Mediated Ring Expansion of Hemiaminals into Epoxide‐Fused Azepines

The planet of the azepines: Epoxy-fused azepines have been synthesized in a highly selective reaction with hemiaminals and vinyl sulfonium salts. Stereochemistry is controlled by the substituent at the four- or five-position of the hemiaminal. The key step involves ring-opening of the hemiaminal, conjugate addition onto a vinyl sulfonium salt, and epoxidation of the aldehyde by the in situ formed sulfur ylide.