Advances in Free Radical Reactions of Organoselenium and Organotellurium Compounds

Abstract

Free radical reactions of organoselenium and tellurium compounds have been widely studied and exploited since the first two volumes of this series appeared. Alkyl aryl selenides and tellurides undergo alkyl C‐Se or C‐Te cleavage with stannanes or silanes to generate alkyl radicals that can be employed in reductions, allylations and both intermolecular and intramolecular additions to a large variety of unsaturated substrates, terminated by either hydrogen or arylchalcogen transfer. Selenoesters, telluroesters and related species generate acyl radicals that are useful in overall decarboxylations of carboxylic acids, and in addition and radical cyclization processes, including cascade reactions of polyenes to afford polycyclic products. Homolytic cleavage of diselenides and ditellurides produces selenyl and telluryl radicals that can be employed in additions to unsaturated acceptors, while the dichalcogenides themselves function as effective trapping agents for radicals produced in a variety of other ways, as from Barton thiohydroxamates. Selenols are efficient hydrogen donors that are of importance in kinetic studies of radical processes. When selenium and tellurium are joined to other heteroatoms, the resulting reagents effect radical 1,2‐additions to unsaturated substrates, as in the case of selenosulfonation and azidoselenenylation reactions. Other radical processes include oxidations, S H 2 substitutions, single electron transfers, extrusions and fragmentations, and reactions performed on solid supports. The synthetic utility of these processes, as well as mechanistic considerations are covered in this chapter.