Upon irradiation with near-UV or visible light, organic diselenides undergo homolytic cleavage of their
selenium-selenium linkage to generate the corresponding seleno radicals, which can add to alkynes, allenes, and related
unsaturated compounds. In the case of alkynes, vicinally diselenated alkenes are synthesized successfully. Photoinduced
bisselenation of allenes takes place selectively at the terminal double bond of allenes. In sharp contrast, photoinduced
addition of organic diselenides to alkenes is an inefficient process. However, combination of diselenides and disulfides
under photoirradiation conditions results in highly regioselective thioselenation of alkenes based on the higher reactivity
of thio radicals toward alkenes and the higher carbon radical capturing ability of diselenides. Similar conditions can be
employed with a variety of unsaturated compounds such as alkynes, allenes, conjugated dienes, vinylcyclopropanes, and
isocyanides. This protocol can also be applied to selenotelluration, selenophosphination, and perfluoroalkylselenation of
unsaturated compounds. The excellent carbon radical capturing ability of diselenides makes it possible to attain sequential
addition of diselenides to several unsaturated compounds by suppression of polymerization of unsaturated compounds.
When the sequential addition takes place intramolecularly under photoirradiation conditions, cyclic products are obtained
successfully via a radical cyclization process. In addition, novel photoinduced electrocyclic reaction of o-alkynylaryl
isocyanides with diselenides efficiently affords diselenated quinoline derivatives.