Aldol

In organic chemistry, an aldol is a structure consisting of a hydroxy group (-OH) two carbons away from either an aldehyde or a ketone. The name combines the suffix 'ol' from the alcohol and the prefix depending on the carbonyl group, either 'ald' for an aldehyde, or 'ket' for a ketone, in which case it referred to as a 'ketol'. An aldol may also use the term β-hydroxy aldehyde (or β-hydroxy ketone for a ketol). The term "aldol" may refer to 3-hydroxybutanal.

Aldols are the product of a carbon-carbon bond-formation reaction, giving them wide applicability as a precursor for a variety of other compounds.

Synthesis and reactions
Aldols are usually synthesized from an aldol addition reaction using two aldehydes or an aldehyde and a ketone for a ketol. These reactions may also be done intramolecularly to form 5 or 6 member rings or for stereoselective syntheses in the active area of asymmetric synthesis.

Aldols may also undergo a condensation reaction in which the hydroxy group is replaced by a pi bond. The final structure is a reactive α,β-unsaturated carbonyl compound, which can also be used in a variety of other reactions:
 * RC(O)CH2CH(OH)R' →  RC(O)CH=CHR'  +  H2O

Applications
Aldols synthesized from two aldehydes are usually unstable, often producing secondary compounds such as diols, unsaturated aldehydes, or alcohols. Hydroxypivaldehyde is a rare example of a distillable aldol. The aldol 3-hydroxybutanal is a precursor to quinaldine, which is a precursor to the dye quinoline Yellow SS.

Aldols are also used as intermediates in the synthesis of polyketide natural products and drugs such as Oseltamivir and Epothilone.