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The Riley oxidation is a selenium dioxide-mediated oxidation of methylene groups adjacent to carbonyls. It was first reported by Harry Lister Riley and co-workers in 1932. [ 1 ] In the decade that ensued, selenium -mediated oxidation rapidly expanded in use, and in 1939, Andre Guillemonat and co-workers disclosed the selenium dioxide-mediated ...
A number of other reagents bring about this reaction. Scheme 1. Selenium dioxide oxidation. In terms of reaction mechanism, SeO 2 and the allylic substrate react via pericyclic process beginning with an ene reaction that activates the C−H bond. The second step is a [2,3] sigmatropic reaction.
The selenium starting material is reduced to selenium, and precipitates as a red amorphous solid which can easily be filtered off. [10] This type of reaction is called a Riley oxidation. It is also renowned as a reagent for allylic oxidation, [11] a reaction that entails the following conversion Allylic oxidation. This can be described more ...
Selenium forms two oxides: selenium dioxide (SeO 2) and selenium trioxide (SeO 3). Selenium dioxide is formed by the reaction of elemental selenium with oxygen: [5] + It is a polymeric solid that forms monomeric SeO 2 molecules in the gas phase. It dissolves in water to form selenous acid, H 2 SeO 3.
It is prepared by oxidising selenium compounds in lower oxidation states. One method involves the oxidation of selenium dioxide with hydrogen peroxide: SeO 2 + H 2 O 2 → H 2 SeO 4. Unlike the production sulfuric acid by hydration of sulfur trioxide, the hydration of selenium trioxide is an impractical method. [4]
Allyl alcohols in general are prepared by allylic oxidation of allyl compounds, using selenium dioxide or organic peroxides. Other methods include carbon-carbon bond-forming reactions such as the Prins reaction, the Morita-Baylis-Hillman reaction, or a variant of the Ramberg-Bäcklund reaction. Hydrogenation of enones is another route.
The conversion of valencene to nootkatone is an example of allylic oxidation. In the synthesis of some fine chemicals, selenium dioxide is used to convert alkenes to allylic alcohols: [15] R 2 C=CR'-CHR" 2 + [O] → R 2 C=CR'-C(OH)R" 2. where R, R', R" may be alkyl or aryl substituents.
If Y is sulfur, the product can be treated with a thiophil to generate an allylic alcohol in what is known as the Mislow–Evans rearrangement. A [2,3]-rearrangement may result in carbon-carbon bond formation. It can also be used as a ring-expansion reaction. [2]