Aldol

Short description: Organic compound of the form R–CH(OH)–CHR–C(=O)–R

Generalized structure of the aldol moiety: When R3 is -H, it is a β-hydroxy aldehyde, otherwise it is a β-hydroxy ketone.

In organic chemistry, an aldol describes a structural motif consisting of a 3-hydroxy ketone, R–CH(OH)–CHR'–C(=O)–R", or 3-hydroxyaldehyde, R–CH(OH)–CHR'–CH=O. Both are composed of a hydroxy group (–OH) and either a ketone (>C=O) or an aldehyde (–CH=O, which is merely a ketone with a hydrogen substituent). An aldol consisting of a 3-hydroxy ketone is called a β-hydroxy ketone, and an aldol consisting of a 3-hydroxy aldehyde is called a β-hydroxy aldehyde. The term "aldol" may refer to 3-hydroxybutanal.[1][2]

## Contents

* 1 Synthesis and reactions
* 2 Applications
* 3 See also
* 4 References

## Synthesis and reactions

Isomers of generalized aldol.

Aldols are usually the product of aldol addition, i.e. the condensation of two aldehydes.[1] Stereoselective syntheses of aldols is an active area of asymmetric synthesis.

The chemistry of aldols is dominated by one reaction, dehydration:

RC(O)CH2CH(OH)R' → RC(O)CH=CHR' + H2O

## Applications

When two molecules of aldehydes react to form an aldol (β-hydroxy aldehyde), the aldol usually produces secondary compounds since it is unstable.[1] Secondary compounds can be diols, unsaturated aldehydes, or alcohols.[1] The aldol 3-hydroxybutanal is a precursor to quinaldine, a precursor to the dye quinoline Yellow SS.[1]

Aldols are also used as intermediates in the synthesis of natural products and drugs.[3][4] The synthesis of Oseltamivir, an antiviral medicine used to treat the flu, involves the aldol reaction.[5]

The structural motif of aldols is often found in polyketide natural products, which can be used to manufacture antibiotics.[3]

Hydroxypivaldehyde is a rare example of a relatively robust aldol.[6]

## See also

* Mukaiyama aldol addition

## References

1. ↑ 1.0 1.1 1.2 1.3 1.4 Kohlpainter, Christian; Schulte, Markus; Falbe, Jürgen; Lappe, Peter; Weber, Jürgen; Frey, Guido D. (15 January 2013). "Aldehydes, Aliphatic". Ullmann's Encyclopedia of Industrial Chemistry (7). doi:10.1002/14356007.a01_321.pub3. ISBN 9783527303854. https://onlinelibrary.wiley.com/doi/full/10.1002/14356007.a01_321.pub3?saml_referrer. Retrieved 1 April 2023.
2. ↑ PubChem. "CID 21282929" (in en). https://pubchem.ncbi.nlm.nih.gov/compound/21282929.
3. ↑ 3.0 3.1 Schetter, Bernd; Mahrwald, Rainer (2006). "Modern aldol methods for the total synthesis of polyketides". Angewandte Chemie International Edition 45 (45): 7506–25. doi:10.1002/anie.200602780. PMID 17103481.
4. ↑ Ghosh, Arun K.; Dawson, Zachary L. (2009). "Synthesis of Bioactive Natural Products by Asymmetric syn- and anti-Aldol Reactions". Synthesis 2009 (17): 2992–3002. doi:10.1055/s-0029-1216941. PMID 30443084.
5. ↑ Ko, Ji S.; Keum, Ji E.; Ko, Soo Y. (15 October 2010). "A synthesis of oseltamivir (Tamiflu) starting from D-mannitol". J Org Chem 75 (20): 7006–9. doi:10.1021/jo101517g. PMID 20866058. https://pubmed.ncbi.nlm.nih.gov/20866058/.
6. ↑ Zhang, Yanping; Mu, Hongliang; Pan, Li; Wang, Xuling; Li, Yuesheng (21 May 2018). "Robust Bulky [P,O] Neutral Nickel Catalysts for Copolymerization of Ethylene with Polar Vinyl Monomers". ACS Catal. 8 (7): 5963–5976. doi:10.1021/acscatal.8b01088.

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