Preparation of novel selenapenams and selenacephems by nucleophilic and radical chemistry involving benzyl selenides

2,2a-Dihydro-1H, 8H-azeto[2,1-b][1,3] benzoselenazin-1-one (12), 5-selena-1-azabicyclo[4.2.0] oct-3-en-8-one (13), ethyl 1-aza-7-oxo-4-selenabicyclo[3.2.0] heptane-2-carboxylate (16), and benzoselenopenem (33) can be prepared in 39 - 85% yield through the intramolecular homolytic substitution of aryl, vinyl or alkyl radicals at the selenium atom in suitably-substituted 4-benzylseleno-beta-lactams, or through intramolecular nucleophilic substitution by the benzylseleno moiety in 4-halo-beta-lactam precursors. Application of this chemistry to the preparation of optically active selenium-containing analogues of beta-lactam antibiotics is also detailed.