Organoselenium chemistry#Selenoxide oxidations

The Riley - oxidation is a name reaction in organic chemistry and named after the chemist HL Riley ( 1899-1986 ). It is a selective, controlled oxidation method of ketones and alkenes, with the carbonyl group or the C = C double bond α - position carbon atom is oxidized to the highly toxic selenium dioxide to the aldehyde, ketone or alkene. Suitable solvents are dioxane, a mixture of acetic acid and acetic anhydride or water in question.

Response Table

• An allylic methyl group (or methylene group or methine group ) can be oxidized to the alcohol by the oxidation Riley, when a solvent is used. A ketone or aldehyde produced, when operating in the gas phase.

• A constant α - methyl group (or methyl group ) of carbonyl compounds can be oxidized with selenium dioxide to the 1,2- dicarbonyl compound:

Reaction mechanism

In this section, the first two mechanisms of overview reactions are described. If an alkene 1 brought with selenium dioxide to react, so initially carries out a nucleophilic attack of the double bond on the selenium of Selendioxids. Here, a proton is transferred. After a few electron pair rearrangements then arises the oxidized allylic intermediate 3, the desired allyl alcohol 4 delivers to the elimination of selenium.

If the ketone 5 brought with selenium dioxide to the reaction, the first reaction step is determined by a nucleophilic attack on the selenium of Selendioxids by the carbonyl group of the ketone here. Here, a proton is transferred and received the ketone 7 as an intermediate for further electron pair rearrangements. In the last step, elemental selenium, and water is split off, so that the desired 1,2- dicarbonyl compound 8 is produced.

Advantages and Disadvantages

• A particular advantage of the reaction is the absence of the further oxidation of aldehydes, to carboxylic acids, as often observed in case of other oxidizing agents.
• The reaction is very specific for oxo compounds and alkenes.
• A disadvantage is the high toxicity of Selendioxids used.