E-rotamers of 3-hydroy cephem derivatives

A process for the manufacture of 7-acylamino-3-hydroxy-cephem-4-carboxylate-1-oxide in E-rotamer form (Formula III), comprises reacting a 7-acylamino-3-exomethylenecepham-4-carboxylate-1-oxide with ozone in an inert organic solvent in the presence of a catalytic amount of an organic or inorganic base at a temperature ranging from about -80 DEG C. to about +20 DEG C. The E-rotamer (wherein the 3-hydroxy group is strongly hydrogen bonded to the carbonyl of the 4-ester group) exhibits different chemical and physical properties from and is more thermodynamically stable than, the Z-rotamer (wherein there is no hydrogen bonding between the 3-hydroxy group and the carbonyl of the 4-ester group).