Chapter 15
α-Carbon Chemistry: Enols, Enolates, and Enamines
Reactividad de los enoles
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 ...
Reactividad de los iones enolato
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, ...
Tipos de Enoles y Enolatos
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 ...
Convenciones del mecanismo de enolato
When a carbonyl compound is treated with a strong base, the α position gets deprotonated to give a resonance-stabilized intermediate called an ...
Formación regioselectiva de enolatos
As depicted in the figure below, the unsymmetrical ketones can form two possible enolates: less substituted or more substituted enolates. Usually, ...
Efectos estereoquímicos de la enolización
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-halogenación de aldehídos y cetonas catalizada por ácido
By replacing an α-hydrogen with a halogen, acid-catalyzed α-halogenation of aldehydes or ketones yields a monohalogenated product
In the first ...
α-halogenación de aldehídos y cetonas promovida por bases
α-Halogenation of aldehydes and ketones is a reaction involving the substitution of α hydrogens with halogens in the presence of a base. ...
Halogenación múltiple de metilcetonas: reacción de 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-Halogenación de derivados del ácido carboxílico: descripción general
Unlike aldehydes and ketones, carboxylic acids do not readily participate in α halogenation reactions via enols or enolate intermediates. However, ...
α-bromación de ácidos carboxílicos: reacción Hell-Volhard-Zelinski
The method to achieve α-brominated carboxylic acids using a mixture of phosphorus tribromide and bromine is known as the ...
Reacciones de compuestos α-halocarbonílicos: sustitución nucleofílica
Nucleophilic substitution in α-halocarbonyl compounds can be achieved via an SN2 pathway. The reaction in α-haloketones is generally carried out ...
Nitrosación de enoles
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 ...
Formación de enlaces C-C: descripción general de la condensación aldólica
Aldol condensation is an important route in synthetic organic chemistry used to generate a new carbon–carbon bond under basic or acidic conditions. ...
Reacción de adición aldólica catalizada por bases
As depicted in Figure 1, base-catalyzed aldol addition involves adding two carbonyl compounds in aqueous sodium hydroxide to form a β-hydroxy ...
Reacción de adición de aldo catalizada por ácido
The aldol reaction of a ketone under acidic conditions successfully forms an unsaturated carbonyl as the final product instead of an aldol. The ...
Deshidratación de aldólicas a enales: condensación de aldólicas catalizada por bases
This lesson delves into the aldol condensation catalyzed by bases, where aldols undergo dehydration to enals. As shown in Figure 1, the β-hydroxy ...
Deshidratación de aldólicas a enonas: condensación de aldólica catalizada por ácido
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. ...
Reacción aldólica intramolecular
Intramolecular aldol reaction occurs in dicarbonyl compounds such as dialdehydes, diketones, and keto-aldehydes. The dicarbonyl compounds possess more ...
Escisión de enlaces C-C: reacción retro-aldólica
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 ...
Reacciones aldólicas cruzadas: descripción general
Crossed aldol addition is the reaction between two different carbonyl compounds under acidic or basic conditions. Here, both the carbonyl compounds ...
Reacción aldólica cruzada con bases débiles
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 ...
Cetonas con aldehídos aromáticos no enolizables: condensación 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 ...
Reacción aldólica cruzada con bases fuertes: reacción aldólica dirigida
The reaction between two different carbonyl compounds comprising α hydrogen in the presence of a strong base like lithium diisopropylamide (LDA) to ...
Condensación aldólica con β-Diesters: Condensación Knoevenagel
The Knoevenagel condensation is an aldol-type reaction involving the condensation of aldehydes or ketones with active methylene compounds such as ...
De ésteres a β-cetoésteres: descripción general de la condensación de Claisen
Regular Claisen condensation is a base-promoted reaction involving identical esters with two α hydrogens, condensing to produce β-ketoesters. It ...
Ésteres a β-cetoésteres: mecanismo de condensación de Claisen
Regular Claisen condensation involves the synthesis of β-ketoesters by combining identical ester molecules bearing two α hydrogens in the ...
Condensación aldólica vs condensación de Claisen
Aldol condensation is an acid or base-catalyzed condensation between aldehydes or ketones to give an α,ꞵ-unsaturated carbonyl compound. A ...
Condensación intramolecular de Claisen de ésteres dicarboxílicos: ciclación de Dieckmann
Dieckmann cyclization is an intramolecular Claisen condensation of diesters. The reaction occurs in the presence of a base and generates a cyclic ...
Compuestos β-dicarbonílicos a través de condensaciones cruzadas de Claisen
Crossed Claisen condensations are base-promoted reactions between two different ester molecules producing β-dicarbonyl compounds. The reaction ...
α-alquilación de cetonas a través de iones enolato
Ketones with α protons are deprotonated by strong bases like lithium diisopropylamide (LDA) to form enolate ions. The anion is stabilized by ...
Factores que afectan a la α-alquilación de cetonas: elección 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 ...
Alquilación de enolatos de β-cetóster: síntesis de ésteres acetoacéticos
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 ...
Alquilación de enolatos de β-diéster: síntesis de ésteres malónicos
Malonic ester synthesis is a method to obtain α substituted carboxylic acids from ꞵ-diesters such as diethyl malonate and alkyl halides.
The ...
Adición conjugada a compuestos carbonílicos α,β-insaturados
α,β-Unsaturated carbonyl compounds are molecules bearing a carbonyl and alkene functionality in conjugation with each other. The conjugation in ...
Suma conjugada (1,4-adición) vs adición directa (1,2-suma)
α,β-Unsaturated carbonyl compounds with two electrophilic sites, the carbonyl carbon, and the β carbon, are susceptible to nucleophilic ...
Adición conjugada de enolatos: Adición de Michael
The attack of a nucleophile at the β carbon of an α,β-unsaturated carbonyl compound is called conjugate addition. Conjugate addition ...
Ciclohexenonas a través de la adición de Michael y la condensación aldólica: la anulación 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, ...
Síntesis de compuestos carbonílicos α sustituidos: la reacción de la enamina de la cigüeña
α-Substituted ketones or aldehydes can be synthesized from enamines by the Stork enamine reaction, named after its pioneer Gilbert Stork. Enamines ...
Aldehídos no enolizables a ácidos y alcoholes: la reacción 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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