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A Two-Step Protocol for Umpolung Functionalization of Ketones Via Enolonium Species
Published on: August 16, 2018
Clarification of the role of water in proline-mediated aldol reactions
Natalia Zotova1, Axel Franzke, Alan Armstrong
1Department of Chemical Engineering and Chemical Technology, Imperial College London, London SW7 2AZ, United Kingdom.
Journal of the American Chemical Society
|November 16, 2007
Abstract
No abstract available in PubMed .
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Aldol condensation is an important route in synthetic organic chemistry used to generate a new carbon–carbon bond under basic or acidic conditions. The aldol condensation reaction presented in Figure 1 constitutes an aldol addition reaction followed by the dehydration process.
Base-Catalyzed Aldol Addition Reaction
As depicted in Figure 1, base-catalyzed aldol addition involves adding two carbonyl compounds in aqueous sodium hydroxide to form a β-hydroxy carbonyl compound.
Acid-Catalyzed Aldol Addition Reaction
The aldol reaction of a ketone under acidic conditions successfully forms an unsaturated carbonyl as the final product instead of an aldol. The acid-catalyzed aldol reaction is depicted in Figure 1.
Dehydration of Aldols to Enals: Base-Catalyzed Aldol Condensation
This lesson delves into the aldol condensation catalyzed by bases, where aldols undergo dehydration to enals. As shown in Figure 1, the β-hydroxy aldehyde formed in a base-catalyzed aldol addition reaction dehydrates on heating to yield an unsaturated carbonyl product, which is commonly referred to as an enal.
Aldol Condensation vs Claisen Condensation
Aldol condensation is an acid or base-catalyzed condensation between aldehydes or ketones to give an α,ꞵ-unsaturated carbonyl compound. A base-promoted condensation between ester molecules to produce a ꞵ-ketoester is known as the Claisen condensation. In the presence of a base, both reactions involve deprotonation of the acidic α hydrogen to produce the corresponding enolates. The nucleophilic enolates attack their respective nonenolized carbonyl compound forming a tetrahedral intermediate.
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