Brønsted Acid-Initiated Formal [1,3]-Rearrangement Dictated by β-Substituted Ene-Aldimines.

The rearrangement of ene-aldimines is a useful reaction for affording homoallylic amines. Despite their utilities in synthetic chemistry, the rearrangement for accessing homoallylic amines substituted at the 2-position remains elusive. In this study, the Brønsted acid-initiated formal [1,3]-rearrangement of ene-aldimines was developed to synthesize 2,4,4-substituted homoallylic amines that were otherwise inaccessible previously. Our study reveals an intermolecular pathway in which the rearrangement proceeds via a protonation-mediated 2-azaallenium cation.