A New Route to Semisynthetic Cephalosporins from Deacetylcephalosporin C. I. Synthesis of 3-Heterocyclicthiomethyl-cephalosporins

New compounds 3-acetoacetoxymethyl-7β-acylaminoceph-3-em-4-carboxylic acids (4) were synthesized from deacetylcephalosporin C (3a), after N-protection of the amino-adipoyl group followed by acetoacetylation of the 3'-hydroxyl with diketene and acyl exchange at the 7-position. They underwent a facile nucleophilic displacement of the 3'-acetoacetoxy group with heterocyclic thiols to afford 7β-acylamino-3-heterocyclicthio-methylceph-3-em-4-carboxylic acids (6) including SCE-963 (6e) in good yields.