Selenium dioxide, allylic mechanism

Treatment of double-bond compounds with selenium dioxide introduces an OH group into the allylic position (see also 19-14). This reaction also produces conjugated aldehydes in some cases.Allylic rearrangements are common. There is evidence that the mechanism does not involve free radicals but includes two pericyclic steps (a and... 

Selenium dioxide is a useful reagent for allylic oxidation of alkenes. The products can include enones, allylic alcohols, or allylic esters, depending on the reaction conditions. The mechanism consists of three essential steps (a) an electrophilic ene reaction with Se02, (b) a [2,3]-sigmatropic rearrangement that restores the original location of the double bond, and (c) solvolysis of the resulting selenium ester.183... 

The selenium-dioxide mediated allylic oxidation of alkenes was explored by means of 2H and 13C KIEs to clarify the mechanism of ene step.85 Changes of isotopic composition were determined for unreacted 2-methyl-2-butene 33 in reaction with Se02 at 25°C in ferf-butyl alcohol (Equation (49)). 

Selenium dioxide oxidation of isopulegol acetate (133 3R) and neoisopulegol acetate (133 35) is reported 223 allylic oxidation is consistent with the Sharpless mechanism but a different mechanism is proposed. 

Woggon, W. D., Ruther, F., Egli, H. The mechanism of allylic oxidation by selenium dioxide. J. Chem. Soc., Chem. Common. 1980, 706-708. 

Singleton, D. A., Hang, C. Isotope effects and the mechanism of allylic hydroxylation of alkenes with selenium dioxide. J. Org. Chem. 2000, 65, 7554-7560. 

Selenium dioxide (Se02) is commonly used to hydroxylate alkenes in the al-lylic position. The mechanism of this transformation involves two sequential peri-cyclic reactions. The first reaction is an ene reaction. It gives a selenenic acid. Then a [2,3] sigmatropic rearrangement occurs, and the intermediate loses SeO to give the observed product. Note how two allylic transpositions result in no al-lylic transposition at all ... 

Treatment of the fraw.Mrart.s-germacranolide, epitulipanolide (477) and two of its derivatives with selenium dioxide and t-butyl hydroperoxide gives the melampolide-type alcohol (478).218 A mechanism for this allylic oxidation with inversion of configuration at the A1-10 double bond is proposed. It should be noted, however, that this is not the first report of such a process (cf. Vol. 11, p. 55). 

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