Nucleophilic and radical chemistry of benzylselenides: preparation of novel selenocephems and selenopenams

Selenocephems (14 and 15) and selenopenams (18, 20, 24 and 25) can be prepared in 18–85% yields through the intramolecular homolytic substitution of aryl or alkyl radicals at the selenium atom in suitably-substituted 4-benzylseleno-β-lactams, or through intramolecular nucleophilic substitution by the benzylseleno moiety in 4-halo-β-lactam precursors.