Copper(II)-Mediated Intramolecular Cyclopropanation of Ketene N,X‑Acetals (X = S, O, N) under Mild Conditions

CuBr2-mediated intramolecular oxidative cyclopropanation of α-oxo ketene N,S-acetals was efficiently achieved to afford 2-thioalkyl-3-azabicyclo-[3.1.0]­hexenes under mild conditions. 2-Oxyalkyl- and 2-aminoallyl-3-azabicyclo-[3.1.0]­hexenes were also obtained from the corresponding α-oxo ketene N,O- and N,N-acetals. Further C–S bond transformations led to diverse 2-aryl-substituted 3-azabicyclo[3.1.0]­hexene derivatives in good to high yields.