Selenium dioxide, allylic

Among eariy synthetic exanqiles of selenium dioxide allylic oxidation s is Rapopoit s synthesis of siienin (. S Oxidation of (7) with selenium dioxide in ethanol at 90 C for 13 h gave a mixture of... 

While most synthetic examples of selenium dioxide allylic oxidation now involve more sophisticated systems (see below), use of the simple stoichiometric reagent alone is still popular. One recent example which well illustrates the mildness and possible selectivity of the reaction is shown in equation... 

A useful modification of selenium dioxide allylic oxidation was introduced by Sharpless in 1977. An inevitable complication of the normal reaction is the production of odoriferous low-valent selenium species which may be difficult to remove from the product mixtures and which can give rise to organo-selenium by-products. Sharpless provided a solution to this problem by the introduction into tlw re-... 

Evidence for the preferential formation of the rraRS-substituted product of selenium dioxide allylic oxidation is seen in the synthesis of part of (13Z)-retinoic acid (equation 48). Reaction took place exclusively at the exocyclic double bond without rearrangement. Allylic oxidation of this nature has also been used in the synthesis of 6-conjugated 2-pyrones (equation 49). This intermediate was employed in the total synthesis of natural pyrones such as yangonin. 

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