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Aldol Reactions and Aldol-like Reactions

Aldol-like Reactions

Many variations of aldol reaction were established. These work on the same principle as classical aldol reaction does, such as ...

  • ... intramolecular aldol reaction, which yields cyclic compounds.
  • ... crossed aldol reaction, in which two different carbonyl compounds are applied together, resulting in a variety of products.
  • ... Knoevenagel reaction, in which particularly strongly CH-acidic compounds, such as 1,3-dicarbonyl compounds or nitroalkanes, are applied instead of a "simple" enolate.
  • ... Michael reaction, in which the conjugated base (anion) of a CH-acidic compound is added to the β carbon of an α,β-unsaturated carbonyl compound. If the CH-acidic compound is an aldehyde or a ketone, the Michael reaction yields a 1,5-dicarbonyl compound.
  • ... Robinson annulation, which is a combination of a Michael reaction and a subsequent intramolecular aldol condensation. Robinson annulation is useful for the construction of complex aliphatic ring skeletons, such as that of steroids and terpenes.
Tab.1
Aldol-like reactions.
Intramolecular aldol condensation: An intramolecular aldol reaction yields a cyclic compound.
Fig.1
Crossed aldol reaction: In crossed aldol reactions, two different carbonyl compounds are applied together, resulting in a variety of products.
Fig.2
Knoevenagel condensation: In Knoevenagel condensation, particularly strongly CH-acidic compounds, such as 1,3-dicarbonyl compounds or nitroalkanes, are applied instead of a "simple" enolate.
Fig.3
Michael reaction: In the Michael reaction, the conjugated base (anion) of a CH-acidic compound is added to the β carbon of an α,β-unsaturated carbonyl compound. As the remaining proton is finally added to the carbonyl oxygen, a 1,4-addition is produced.
Fig.4
Robinson annulation: Robinson annulation is a combination of a Michael reaction and a subsequent intramolecular aldol condensation.
Fig.5

Exercise

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