A process is disclosed for preparing a cephalosporin of structure: ##STR1## where R is selected from the class consisting of hydrogen, alkyl having from 1 to 4 carbon atoms, cyano-methyl, thienyl-methyl, furyl-methyl, naphthyl-methyl, phenyl-methyl, phenoxy-methyl, phenyl-isopropyl, phenoxy-isopropyl, pyridyl-4-thiomethyl, tetrazolyl-1-methyl;R.sup.1 is selected from the class consisting of hydroxy, alkoxy having from 1 to 4 carbon atoms, trichloroethoxy, benzyloxy, p-methoxy-benzyloxy, p-nitrobenzyloxy, benzhydryloxy, triphenylmethoxy, phenacyloxy, p-halophenacyloxy; andZ is selected from the class consisting of hydrogen, hydroxy, --O--Alkyl, --O--CO--Alkyl, --Br, --I, --NH.sub.2, --O--COCH.sub.3, --O--CO--NH.sub.2, and an --S-mononuclear nitrogen heterocyclic ring,Wherein a compound of structure: ##STR2## where R, R.sup.1 and Z have the above meanings, is reacted with iodine in a suitable aqueous solvent at a temperature between 5.degree. and 80.degree. C in the presence of an oxide of a heavy metal or with a free radical initiator under the influence of light or heat, to give a compound of structure: ##STR3## in which R, R.sup.1 and Z have the above meanings, AND THE SAID INTERMEDIATE (II) is reacted in a suitable solvent with a compound selected from the class consisting of inorganic and organic bases to finally give the desired compound (III) which is then isolated and purified in per se known manner.