Norrish reaction

Source: Wikipedia, the free encyclopedia.

A Norrish reaction, named after

polycarbonates and polyketones
.

Type I

The Norrish type I reaction is the photochemical cleavage or

2-butanone largely yields ethyl radicals in favor of less stable methyl radicals.[4]

Norrish type I reaction
Norrish type I reaction

Several secondary reaction modes are open to these fragments depending on the exact molecular structure.

  • The fragments can simply recombine to the original carbonyl compound, with
    racemisation
    at the α-carbon.
  • The acyl radical can lose a molecule of
    α substituents. Typically the more α substituted a ketone is, the more likely the reaction will yield products in this way.[5][6]
  • The abstraction of an α-proton from the carbonyl fragment may form a ketene and an alkane.
  • The abstraction of a β-proton from the alkyl fragment may form an aldehyde and an alkene.
Norrish type I reaction
Norrish type I reaction

The synthetic utility of this reaction type is limited, for instance it often is a side reaction in the Paternò–Büchi reaction. One organic synthesis based on this reaction is that of bicyclohexylidene.[7]

Type II

A Norrish type II reaction is the photochemical

biradical as a primary photoproduct.[8] Norrish first reported the reaction in 1937.[9]

Norrish type II reaction
Norrish type II reaction

Secondary reactions that occur are fragmentation (β-scission) to form an alkene and an enol (which will rapidly tautomerise to a carbonyl), or intramolecular recombination of the two radicals to a substituted cyclobutane (the Norrish–Yang reaction).[10]

Scope

The Norrish reaction has been studied in relation to

chemical yield together with cyclic alcohols (cyclobutanols and cyclopentanols) both from a Norrish type II channel and around 10% yield of hexanal
from a Norrish type I channel (the initially formed n-hexyl radical attacked by oxygen).

In one study

nanometer diameter. The species believed to responsible for reducing Au3+ to Au0[13] is the Norrish generated ketyl
radical.

Norrish application nanogold synthesis
Norrish application nanogold synthesis

Leo Paquette's 1982 synthesis of dodecahedrane involves three separate Norrish-type reactions in its approximately 29-step sequence.

An example of a synthetically useful Norrish type II reaction can be found early in the total synthesis of the biologically active

Phil Baran and coworkers.[14]
The optimized conditions minimize side reactions, such as the competing Norrish type I pathway, and furnish the desired intermediate in good yield on a multi-gram scale.

Type II Norrish reaction in Phil Baran's total synthesis of the biologically active cardenolide ouabagenin.
Type II Norrish reaction in Phil Baran's total synthesis of the biologically active cardenolide ouabagenin.

See also

References

  1. ISBN 0-470-01041-X
  2. S2CID 225243217
    .
  3. ^
    doi:10.1351/goldbook.N04219. Retrieved 31 March 2014. {{cite journal}}: Cite journal requires |journal= (help
    )
  4. doi:10.1021/ja01162a544
    .
  5. doi:10.1021/ja00726a046
    .
  6. doi:10.1016/0047-2670(72)80036-4
    .
  7. ^ Bicyclohexylidene Nicholas J. Turro, Peter A. Leermakers, and George F. Vesley Organic Syntheses, Coll. Vol. 5, p.297 (1973); Vol. 47, p.34 (1967) Online article.
  8. doi:10.1351/goldbook.N04218. Retrieved 31 March 2014. {{cite journal}}: Cite journal requires |journal= (help
    )
  9. S2CID 4104669
    .
  10. doi:10.1351/goldbook.NT07427. Retrieved 31 March 2014. {{cite journal}}: Cite journal requires |journal= (help
    )
  11. doi:10.1021/jo060596u
  12. doi:10.1021/ja066522h
  13. ^ Technically Au3+ is reduced to Au2+ which then forms Au+ and Au3+ by disproportionation followed by final reduction of Au1+ to Auo
  14. PMID 23288535
    .
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