formula 3 str4 in the above formulae 3 and 4 r r 1 r 2 r 3 r 4 r 5 x and z have the same meanings as defined above for formula 1 and y is an acyloxy group such as a c 1 c 4 alkanoyloxy group for example acetoxy or a halo group such as chloro bromo or iodo the reaction is carried out in an inert solvent at a temperature between about 20 u00b0 c and about 65 u00b0 c an excess of the thiazole or substituted thiazole is used for best results when in the formula 2 y is a halo group the reaction proceeds at about room temperature and can be carried out at higher temperatures of up to about 65 u00b0 c when y is an acyloxy group such as acetoxy the reaction is usually carried out with warming at temperatures of about 45 u00b0 c to about 65 u00b0 c a small amount of an iodide salt e g ki when added to the reaction mixture y acyloxy oftentimes enhances the rate and yield of the displacement reaction the compound of the formula 2 wherein r is amino and r 1 is a carboxy substituted alkyl group may be used in the reaction in protected form i e where the amino and carboxy groups are suitably protected with conventional amino and carboxy protecting groups the starting materials formula 2 are obtained by the n acylation of a 7 amino 3 39 substituted 3 cephem nucleus compound with the desired oximino.