Aldol

General aldol structure showing the α and 𝛽 positions of carbons relative to the carbonyl. When R" is -H, it is an aldol, when R" is a carbon, it is a ketol.

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. ^{[1] [2]}

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

Possible stereochemical configurations for chiral aldols. R/S configurations of chiral centers: A: OH is 4R, R-group is 3R B: OH is 4S, R-group is 3S C: OH is 4R, R-group is 3S D: OH is 4S, R-group is 3R

Aldols are usually synthesized from an aldol addition reaction using two aldehydes or an aldehyde and a ketone for a ketol. ^[1] 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. ^[1] Hydroxypivaldehyde is a rare example of a distillable aldol. ^[3] The aldol 3-hydroxybutanal is a precursor to quinaldine, which is a precursor to the dye quinoline Yellow SS. ^[1]

Aldols are also used as intermediates in the synthesis of polyketide natural products and drugs such as Oseltamivir and Epothilone. ^{[4] [5] [6] [7]}

See also

• Aldol reactions
• Beta hydroxycarboxylic acid

References

1. 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 . Retrieved 1 April 2023– via Wiley Online Library.
2. PubChem. "CID 21282929". National Center for Biotechnology Information. Retrieved 2023-04-15.
3. 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 – via ACS Publications.
4. 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.
5. 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. PMC   6233898 . PMID   30443084 – via Thieme.
6. 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.
7. Schinzer, Dieter (2004-06-24), Mahrwald, Rainer (ed.), "The Aldol Reaction in Natural Product Synthesis: The Epothilone Story" , Modern Aldol Reactions (1 ed.), Wiley, pp. 311–328, doi:10.1002/9783527619566.ch7, ISBN   978-3-527-30714-2 , retrieved 2024-04-15