MECHANISM OF ALLYLIC HYDROXYLATION BY SELENIUM DIOXIDE

Both regiochemical and stereochemical aspects of the allylic hydroxylation reactions of selenium dioxide have been investigated. The principal findings are as follows. (1) In terfbutyl alcohol the mechanism is more complex than would be predicted by using the ene-[2,3]sigmatropic shift scheme proposed by Sharpless. (2) The stereochemical complexities appear to derive from ionic intermediates and can be suppressed in more basic media, e.g., fert-butyl alcohol/pyridine. (3) The strong preference for trans allylic alcohol products in the reaction is due to sterie preferences in the [2,3]sigmatropic migration. The ene step is nonselective. © 1979, American Chemical Society. All rights reserved.