Riley oxidation

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Riley oxidation
Named after Harry Lister Riley
Reaction type Organic redox reaction

The Riley oxidation is a

ketones and at the allylic position of olefins is known as the Riley Oxidation.[3]

Mechanism

The mechanism of oxidation of -CH2C(O)R group by SeO2 has been well investigated.

electrophilic
selenium center. Following rearrangement and loss of water, a second equivalent of water attacks the alpha position. Selenic acid is liberated in the final step to give the 1,2-dicarbonyl product.

Allylic oxidation using selenium-dioxide proceeds via an

allylic alcohol product.[4][8]

Scope

The Riley Oxidation is amenable to a variety of carbonyl and olefinic systems with a high degree of regiocontrol based on the substitution pattern of the given system.

Ketones with two available α-methylene positions react more quickly at the least hindered position.:[1]

Allylic oxidation can be predicted by the substitution pattern on the olefin. In the case of 1,2-disubstituted olefins, reaction rates follow CH > CH2 > CH3:

Geminally-substituted olefins react in the same order of reaction rates as above:[2]

Trisubstituted alkenes experience reactivity at the more substituted end of the double bond. The order of reactivity follows that CH2 > CH3 > CH:

Due to the rearrangement of the double bond, terminal olefins tend to give primary allylic alcohols:

Cyclic alkenes prefer to undergo allylic oxidation within the ring, rather than the allylic position at the sidechain. In bridged ring systems, Bredt’s rule is followed and bridgehead positions are not oxidized:

Applications

In their

Epimerization of the alpha hydrogen led to cis-glyoxal, which spontaneously underwent cyclization with the secondary amine to yield dehydrostryninone.[9]

Selenium-dioxide mediated oxidation was used in the synthesis of the diterpenoid ryanodol.[10]

Selenium dioxide mediated allylic oxidation to access ingenol.[11]

References

  1. ^
    ISSN 0368-1769
    .
  2. ^ a b Guillemonat (1939). "Oxidation of ethylenic hydrocarbons using selenium dioxide".
  3. ISBN 978-0-12-429785-2
    .
  4. ^
    ISSN 0022-3263
    .
  5. ISSN 0002-7863
    .
  6. ISSN 0022-3263
    .
  7. doi:10.1016/0040-4020(96)00902-7
    .
  8. doi:10.1021/jo00393a045
    .
  9. S2CID 42677858
    .
  10. PMID 27563092
    .
  11. S2CID 26998997
    .
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