Organoselenium

Organoselenium compounds are organic compounds that contain carbon–selenium bonds. They form a diverse class with roles in organic synthesis and biology. Selenium’s position below sulfur in the periodic table gives C–Se bonds that are relatively large and polarizable, leading to distinctive reactivity and redox behavior.

Common classes include selenols (R–SeH), selenides (R–Se–R' or R–Se–R''), diselenides (R–Se–Se–R'), and selenoxides (R–Se(O)–R'). Selenols are notably more acidic than thiols and alcohols. Selenides act as nucleophiles and can be oxidized to diselenides or selenoxides. Selenoxides arise by oxidation of selenides and can undergo Cope elimination to form alkenes and selenium-containing byproducts.

In synthesis, selenium dioxide (SeO2) is a classical reagent for allylic oxidation, illustrating the utility of organoselenium species in transformations beyond simple C–Se bond formation. Organoselenium chemistry also intersects with biology, where selenium is essential in the amino acid selenocysteine, a component of several antioxidant enzymes such as glutathione peroxidase.

Preparation and handling typically involve introducing selenium into organic frameworks via nucleophilic selenium sources, followed by oxidation to diselenides or selenoxides, or formation of selenols through reduction of higher selenium species. Many organoselenium compounds are toxic and have characteristic odors, so appropriate safety precautions are essential.

Overall, organoselenium chemistry provides versatile tools for selective oxidations, carbon–carbon and carbon–heteroatom bond formation, and explorations of selenium’s roles in biology and medicine.