METAL-CATALYZED AND METAL-PROMOTED CYCLIZATIONS FOR THE SYNTHESIS OF CEPHALOSPORINS - A POSSIBLE DAOC/DAC SYNTHETASE BIOMIMETIC PROCESS

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 FeCl3 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.