Abstract: A process is described for preparing 3-exomethylene cephalosporanic acid derivatives for use in the synthesis of cephalosporin antibiotics such as ceftibuten. The process comprises electrochemical reduction of a compound of the formula (IV) ##STR1## wherein: R.sup.3 is ##STR2## is an optional sulfoxide group; n is 2 or 3; R.sup.1 is H and R is H or NHR.sup.2, where R.sup.2 is H or a protecting group selected from C.sub.6 H.sub.5 CH.sub.2 OC(O)--, C.sub.6 H.sub.5 C(O)-- or C.sub.1 -C.sub.6 alkoxy-C(O)--; or wherein R and R.sup.1 together with the carbon atom to which they are attached comprise --C(O)--, and produces the desired 3-exomethylene compounds with low levels of the corresponding 3-methyl tautomers.

Abstract: A process is described for preparing 3-exomethylene cephalosporanic acid derivatives for use in the synthesis of cephalosporin antibiotics such as ceftibuten. The process comprises electrochemical reduction of a compound of the formula (IV) ##STR1## wherein: R.sup.3 is CH.sub.3 C(O)--; ##STR2## is an optional sulfoxide group; n is 2 or 3; R.sup.1 is H and R is H or NHR.sup.2, where R.sup.2 is H or a protecting group selected from C.sub.6 H.sub.5 CH.sub.2 OC(O)--, C.sub.6 H.sub.5 C(O)-- or C.sub.1 -C.sub.6 alkoxy-C(O)--; or wherein R and R.sup.1 together with the carbon atom to which they are attached comprise --C(O)--, and produces the desired 3-exomethylene compounds with low levels of the corresponding 3-methyl tautomers.