Robust Synthesis of N‑Sulfonylazetidine Building Blocks via Ring Contraction of α‑Bromo N‑Sulfonylpyrrolidinones

A simple and robust one-pot nucleophilic addition–ring contraction of α-bromo N-sulfonylpyrrolidinones has been achieved toward α-carbonylated N-sulfonylazetidines. In the presence of potassium carbonate, various nucleophiles, such as alcohols, phenols or anilines, have been efficiently incorporated into the azetidine derivatives. Moreover, the α-bromopyrrolidinone precursors could be selectively obtained in good yields by monobromination of cheap and easily available N-sulfonyl-2-pyrrolidinone derivatives.