Ester cleavage process for use with .beta.-lactams

A process for producing a compound of the formula I ##STR15## or a pharmaceutically acceptable salt thereof;

• which comprises reacting, in a non-basic solvent having a dielectric constant between about 0 and about 15, lithium iodide and a compound of the formula II or a salt of a compound of the formula II that is capable of forming a salt, ##STR16## wherein:
• W is lithium ion;
• W.sup.1 is a carboxy-protecting group;
• Z is --S--, --S(O)--, --SO.sub.2 -- or --CH.sub.2 --;
• R.sup.9 is hydrogen, C.sub.1 -C.sub.6 alkyl or is combined with R.sup.10 to form a double bond;
• R.sup.10 is hydrogen or is combined with R.sup.9 to form a double bond;
• f is 0 or 1, with the provisos that when f is 1, R.sup.9 and R.sup.10 combine to form a double bond and when f is 0, A is C.sub.1 -C.sub.6 alkyl;
• R.sup.1 and R.sup.2 are independently hydrogen, C.sub.1 -C.sub.6 alkyl, amino-protecting group or --C(O)--R where R is the residue of a carboxylic acid, with the proviso that when one of R.sup.1 or R.sup.2 is --C(O)--R then the other cannot be hydrogen;
• A is hydrogen or a substituent selected from those found in the cephalosporin, 1-carbacephalosporin or penicillin arts.