α,β-Unsaturated carbonyl compound

Source: Wikipedia, the free encyclopedia.
General structure of α,β-unsaturated carbonyl compounds.
R2 & R4 can also be single hydrogens.

α,β-Unsaturated carbonyl compounds are

vinylogous. Examples of unsaturated carbonyls are acrolein (propenal), mesityl oxide, acrylic acid, and maleic acid. Unsaturated carbonyls can be prepared in the laboratory in an aldol reaction and in the Perkin reaction
.


Classifications

α,β-Unsaturated carbonyl compounds can be subclassified according to the nature of the carbonyl and alkene groups.

Acryloyl group

Structure of the acryloyl group

α,β-Unsaturated carbonyl compounds featuring a carbonyl conjugated to an alkene that is terminal, or

acyl group derived from acrylic acid. The preferred IUPAC name
for the group is prop-2-enoyl, and it is also known as acrylyl or simply (and incorrectly) as acryl. Compounds containing an acryloyl group can be referred to as "acrylic compounds".

α,β-Unsaturated acids, esters, and amides

An α,β-unsaturated acid is a type of α,β-unsaturated carbonyl compound that consists of an

polyacrylate plastics. Acrylate polymers are derived from but do not contain the acrylate group.[4] The carboxyl group of acrylic acid can react with ammonia to form acrylamide, or with an alcohol to form an acrylate ester. Acrylamide and methyl acrylate are commercially important examples of α,β-unsaturated amides
and α,β-unsaturated esters, respectively. They also polymerize readily. Acrylic acid, its esters, and its amide derivatives feature the acryloyl group.

α,β-Unsaturated dicarbonyls are also common. The parent compounds are

Krebs citric acid cycle
, which is of great importance in bioenergy.

Enones

"Enone" redirects here. For the character in Greek mythology, see
Oenone. For enone biomolecules used in paleothermometry, see Alkenone
.

An enone (or alkenone) is an organic compound containing both

propargyl alcohol. Another method to access α,β-unsaturated carbonyls is via selenoxide elimination. Cyclic enones can be prepared via the Pauson–Khand reaction
.

General reaction for an aldol condensation between two carbonyl compounds

Cyclic enones

The cyclic enones include cyclopropenone, cyclobutenone,[6] cyclopentenone, cyclohexenone, and cycloheptenone.[7]

Enals

An enal (or alkenal) is an organic compound containing both alkene and aldehyde functional groups. In an α,β-unsaturated enal, the alkene is conjugated to the carbonyl group of the aldehyde (formyl group).[3] The simplest enal is acrolein (CH2=CHCHO). Other examples include cis-3-hexenal (essence of mowed lawns) and cinnamaldehyde (essence of cinnamon).

Reactions of α,β-unsaturated carbonyls

α,β-Unsaturated carbonyls are

Michael addition, which is used commercially in the conversion of mesityl oxide into isophorone. Owing to their extended conjugation, α,β-unsaturated carbonyls are prone to polymerization. In terms of industrial scale, polymerization dominates the use of α,β-unsaturated carbonyls. Again because of their electrophilic character, the alkene portion of α,β-unsaturated carbonyls is good dienophiles in Diels–Alder reactions. They can be further activated by Lewis acids, which bind to the carbonyl oxygen. α,β-Unsaturated carbonyls are good ligands for low-valent metal complexes, examples being Fe(bda)(CO)3 and tris(dibenzylideneacetone)dipalladium(0)
.

α,β-Unsaturated carbonyls are readily hydrogenated. Hydrogenation can target the carbonyl or the alkene (

conjugate reduction
) selectively, or both functional groups.

Enones undergo the Nazarov cyclization reaction and in the Rauhut–Currier reaction (dimerization).

α,β-Unsaturated thioesters

α,β-Unsaturated thioesters are intermediates in several enzymatic processes. Two prominent examples are

crotonyl-coenzyme A. They arise by the action of acyl-CoA dehydrogenases.[8] Flavin adenine dinucleotide
(FAD) is a required co-factor.

Safety

Since α,β-unsaturated compounds are electrophiles and alkylating agents, many α,β-unsaturated carbonyl compounds are toxic. The endogenous scavenger compound

N-acetylcysteine
) containing thiol groups may protect from such harmful alkylation.

See also

References

  1. ISBN 9780470772218
    .
  2. ISBN 9780470772225
    .
  3. ^
    ISBN 978-0-471-72091-1
  4. ISBN 978-3527306732
    .
  5. ISBN 978-3527306732
    .
  6. doi:10.15227/orgsyn.089.0491
    .
  7. doi:10.15227/orgsyn.059.0113
    .
  8. S2CID 42549744
    .
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