Tf₂O‑Promoted Intramolecular Schmidt Reaction of the ω‑Azido Carboxylic Acids

A designed Tf₂O-promoted intramolecular Schmidt reaction of 2-substituted ω-azido carboxylic acids was demonstrated. Tf₂O was used as an activation reagent for the carboxylic acid, and ω-azido anhydride was in situ generated, releasing a molecular TfOH, which acted as an acid promoter for the Schmidt process. A series of 2-substituted pyrrolidines was produced and acetylated for better purification. The strategy was also efficient for conversion of a 4-substituted ω-azido carboxylic acid to the tricyclic lactam.