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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.

Photolyses of the thiohydroximate ester derivatives 13 and 21 of the 4-(benzyl-seleno)-2-azetidinoines 7 and 20, afford the 1-aza-7-oxo-4-selenabicyclo-[3.2.0]heptane ring systems 14 and 21 in good to moderate yield in processes that presumably involve intramolecular homolytic substitution at selenium with expulsion of benzyl radical. Extension of this methodology to the preparation of derivatives 24 of 12,2a-dihydro-1H,8H-azeto[2,1-b][1,3]benzoselenazin-1-one (22) is also described.

The reductive dehalogenation of organohalides by tris(trimethylsilyl)methane has been re-investigated. Contrary to claims made in a recent publication (Tetrahedron Lett. 2006, 47, 5163-5165), (TMS) 3 CH does not reduce organohalides. In competition experiments between (TMS) 3 CH and the poor chain mediator Et 3 SiH, the latter performed the reduction. Computational investigations support these experimental findings and indicate that the C-H bond of (TMS) 3 CH is too strong for this compound to serve as an effective mediator of radical reactions.

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