Metal‐Catalyzed and ‐Promoted Cyclizations for the Synthesis of Cephalosporins: A Possible DAOC/DAC Synthetase Biomimetic Process.

Abstract A thiyl radical cyclization approach to the sulphur containing ring of cephams is described. The reaction was carried out using metals able to perform a single-electron oxidation process under stoichiometric [Fe(III), MN(OAc) 3 ] or catalytic [Fe(III)] conditions. Furthermore, the FeCl 3 or Mn(OAc) 3 /LiX promoted reactions afforded, by a double single-electron oxidation process, over oxidized compounds. The relationship with the mechanistic hypothesis proposed by Baldwin for the DAOC/DACS-catalyzed ring expansion from Penicillin N to Desacetoxy cephalosporin C is discussed.