Background: Homolytic substitution at higher order chalcogens is no doubt a useful tool for
radical based synthetic methodologies. Intramolecular variants of these reactions have received considerable
attention in recent years and are a reliable route to prepare interesting molecules exhibiting a
diverse range of biological activities. Methods: This review highlights tin-fee and photo-initiated
routes to homolytic substitution at chalcogens. The use of thiohydroximate esters as precursors for
radicals makes intramolecular homolytic substitution reactions easily initiated using near UV light. Intermolecular
variants of these reactions offer to the synthetic practitioner a convenient route to a number
of different radicals whose reactivity can be utilized to form interesting, non-chalcogen containing molecules. Evolving
from the latter method are unique tellurium based radical precursors that do not undergo homolytic substitution but
rather produce synthetically useful radicals by using near UV light. Conclusions: Employing these reactions in synthesis
provides a greener alternative to some traditional radical based methods eliminating the requirement for chemical initiators
and toxic chain carriers. These versatile methods afford atom and chemical efficient processes that can be performed
using low cost white light sources.
Keywords: Chalcogen, homolytic substitution, photoinitiation precursor, radical cyclization, SH2, selenium, tellurium, tin-free.
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