Chapter 15
α-Carbon Chemistry: Enols, Enolates, and Enamines
Réactivité des énols
Enols are a class of compounds where a hydroxyl group is attached to a carbon–carbon double bond, which implies that it is a vinyl alcohol. A ...
Réactivité des ions énolates
Enolate ions are formed by the acid–base reaction of a carbonyl compound with a base. This leads to deprotonation of the α hydrogen atom, ...
Types d’énols et d’énolates
Aldehydes and ketones form enols, although only about 1% of the enol is present at the equilibrium for simple monocarbonyl compounds. The enol form is ...
Conventions du mécanisme énologique
When a carbonyl compound is treated with a strong base, the α position gets deprotonated to give a resonance-stabilized intermediate called an ...
Formation régiosélective des énolates
As depicted in the figure below, the unsymmetrical ketones can form two possible enolates: less substituted or more substituted enolates. Usually, ...
Effets stéréochimiques de l’énolisation
The chiral α-carbon of the carbonyl compound is the stereocenter of the molecule. As shown in the figure below, when such a carbonyl compound ...
α-halogénation d’aldéhydes et de cétones catalysée par un acide
By replacing an α-hydrogen with a halogen, acid-catalyzed α-halogenation of aldehydes or ketones yields a monohalogenated product
In the first ...
α-halogénation des aldéhydes et des cétones promue par une base
α-Halogenation of aldehydes and ketones is a reaction involving the substitution of α hydrogens with halogens in the presence of a base. ...
Halogénation multiple des méthylcétones : réaction haloforme
A method involving the transformation of methyl ketones to carboxylic acids using excess base and halogen is called the haloform reaction. It begins with ...
α-halogénation des dérivés de l’acide carboxylique : aperçu
Unlike aldehydes and ketones, carboxylic acids do not readily participate in α halogenation reactions via enols or enolate intermediates. However, ...
α-bromation des acides carboxyliques : réaction Hell-Volhard-Zelinski
The method to achieve α-brominated carboxylic acids using a mixture of phosphorus tribromide and bromine is known as the ...
Réactions des composés α-halocarbonyles : substitution nucléophile
Nucleophilic substitution in α-halocarbonyl compounds can be achieved via an SN2 pathway. The reaction in α-haloketones is generally carried out ...
Nitrosation des énols
The nitrosation reaction is one of the methods of preparing 1,2-diketones. The enol tautomer of the starting ketone reacts with sodium nitrite in ...
Formation de liaisons C-C : aperçu de la condensation Aldol
Aldol condensation is an important route in synthetic organic chemistry used to generate a new carbon–carbon bond under basic or acidic conditions. ...
Réaction d’addition d’aldol catalysée par une base
As depicted in Figure 1, base-catalyzed aldol addition involves adding two carbonyl compounds in aqueous sodium hydroxide to form a β-hydroxy ...
Réaction d’addition d’aldol catalysée par un acide
The aldol reaction of a ketone under acidic conditions successfully forms an unsaturated carbonyl as the final product instead of an aldol. The ...
Déshydratation d’aldols en enals : condensation d’aldol catalysée par une base
This lesson delves into the aldol condensation catalyzed by bases, where aldols undergo dehydration to enals. As shown in Figure 1, the β-hydroxy ...
Déshydratation des aldols en énones : condensation des aldol catalysée par l’acide
As shown in Figure 1, under acidic conditions, the β-hydroxy ketone undergoes dehydration via an E1 elimination reaction to form an enone.
Figure 1. ...
Réaction intramoléculaire d’aldol
Intramolecular aldol reaction occurs in dicarbonyl compounds such as dialdehydes, diketones, and keto-aldehydes. The dicarbonyl compounds possess more ...
Clivage de la liaison C-C : réaction rétro-aldol
The reverse of the aldol addition reaction is called the retro-aldol reaction. Here, the carbon–carbon bond in the aldol product is cleaved under ...
Réactions d’Aldol croisé : aperçu
Crossed aldol addition is the reaction between two different carbonyl compounds under acidic or basic conditions. Here, both the carbonyl compounds ...
Réaction d’aldol croisée à l’aide de bases faibles
This lesson deals with the crossed aldol reaction using weak bases. The self-condensation of an aldehyde having α hydrogen is prevented by adding it ...
Cétones avec des aldéhydes aromatiques non énolizables : condensation de Claisen-Schmidt
Benzaldehyde, like formaldehyde, lacks an α hydrogen and cannot enolize to form an enolate. Hence, the reaction of benzaldehyde with a ketone in the ...
Réaction d’aldol croisée à l’aide de bases fortes : réaction d’aldol dirigée
The reaction between two different carbonyl compounds comprising α hydrogen in the presence of a strong base like lithium diisopropylamide (LDA) to ...
Condensation Aldol avec β-diesters : condensation de Knoevenagel
The Knoevenagel condensation is an aldol-type reaction involving the condensation of aldehydes or ketones with active methylene compounds such as ...
Esters à β-cétoesters : Présentation de la condensation de Claisen
Regular Claisen condensation is a base-promoted reaction involving identical esters with two α hydrogens, condensing to produce β-ketoesters. It ...
Esters aux β-cétoesters : mécanisme de condensation de Claisen
Regular Claisen condensation involves the synthesis of β-ketoesters by combining identical ester molecules bearing two α hydrogens in the ...
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 ...
Condensation Claisen intramoléculaire d’esters dicarboxyliques : cyclisation de Dieckmann
Dieckmann cyclization is an intramolecular Claisen condensation of diesters. The reaction occurs in the presence of a base and generates a cyclic ...
Composés β-dicarbonyles via condensations croisées de Claisen
Crossed Claisen condensations are base-promoted reactions between two different ester molecules producing β-dicarbonyl compounds. The reaction ...
α-alkylation des cétones via les ions énolates
Ketones with α protons are deprotonated by strong bases like lithium diisopropylamide (LDA) to form enolate ions. The anion is stabilized by ...
Facteurs affectant la α-alkylation des cétones : choix de la base
α-Alkylation of ketones is achieved in the presence of alkyl halides and a base. The reaction proceeds via the formation of an enolate ion followed ...
Alkylation des énolates de β-cétoester : synthèse d’esters acétoacétiques
Acetoacetic ester synthesis is a method to obtain ketones from alkyl halides and β-keto esters. The reaction occurs in the presence of an alkoxide ...
Alkylation des énolates β-diester : synthèse d’esters maloniques
Malonic ester synthesis is a method to obtain α substituted carboxylic acids from ꞵ-diesters such as diethyl malonate and alkyl halides.
The ...
Addition conjuguée à des composés carbonylés α,β-insaturés
α,β-Unsaturated carbonyl compounds are molecules bearing a carbonyl and alkene functionality in conjugation with each other. The conjugation in ...
Addition conjuguée (1,4-addition) vs addition directe (1,2-addition)
α,β-Unsaturated carbonyl compounds with two electrophilic sites, the carbonyl carbon, and the β carbon, are susceptible to nucleophilic ...
Addition conjuguée d’énolates : Addition de Michael
The attack of a nucleophile at the β carbon of an α,β-unsaturated carbonyl compound is called conjugate addition. Conjugate addition ...
Cyclohexenones via Michael Addition et Aldol Condensation : L’annulation de Robinson
Robinson annulation is a base-catalyzed reaction for the synthesis of 2-cyclohexenone derivatives from 1,3-dicarbonyl donors (such as cyclic diketones, ...
Synthèse de composés carbonylés α-substitués : la réaction de l’énamine de la cigogne
α-Substituted ketones or aldehydes can be synthesized from enamines by the Stork enamine reaction, named after its pioneer Gilbert Stork. Enamines ...
Aldéhydes non énolizés en acides et alcools : la réaction de Cannizzaro
The Cannizzaro reaction is a base-promoted redox reaction producing a primary alcohol and a carboxylic acid from two molecules of a nonenolizable ...
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