A 3-step process for the conversion of C-4 disubstituted ceph-2-ems into ceph-3-ems, where the original C-4 carboxyl group is replaced by a substituted ethyl group, is described. A range of novel compounds (A-D) are produced. Ester (B) is converted into carboxylic acid (E). The regiospecificity of alkylation reactions of ceph-3-em sulphides, α- sulphoxides and β-sulphoxides is investigated for a variety of bases and electrophiles. C-4 disubstituted ceph-2-ems thus obtained are converted into the novel β-lactams (F & G). A novel class of ceph-3-ems bearing C-2 exocyclic double bond systems containing two heteroatoms is described (H-J). Ester (H) is converted into acid (L). None of the new β-lactams obtained exhibited any significant biological activity.