Chapter 15
α-Carbon Chemistry: Enols, Enolates, and Enamines
Chapter 15
α-Carbon Chemistry: Enols, Enolates, and Enamines
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 …
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, …
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 …
When a carbonyl compound is treated with a strong base, the α position gets deprotonated to give a resonance-stabilized intermediate called an …
As depicted in the figure below, the unsymmetrical ketones can form two possible enolates: less substituted or more substituted enolates. Usually, …
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 …
By replacing an α-hydrogen with a halogen, acid-catalyzed α-halogenation of aldehydes or ketones yields a monohalogenated product
In the first …
α-Halogenation of aldehydes and ketones is a reaction involving the substitution of α hydrogens with halogens in the presence of a base. …
A method involving the transformation of methyl ketones to carboxylic acids using excess base and halogen is called the haloform reaction. It begins with …
Unlike aldehydes and ketones, carboxylic acids do not readily participate in α halogenation reactions via enols or enolate intermediates. However, …
The method to achieve α-brominated carboxylic acids using a mixture of phosphorus tribromide and bromine is known as the …
Nucleophilic substitution in α-halocarbonyl compounds can be achieved via an SN2 pathway. The reaction in α-haloketones is generally carried out …
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 …
Aldol condensation is an important route in synthetic organic chemistry used to generate a new carbon–carbon bond under basic or acidic conditions. …
As depicted in Figure 1, base-catalyzed aldol addition involves adding two carbonyl compounds in aqueous sodium hydroxide to form a β-hydroxy …
The aldol reaction of a ketone under acidic conditions successfully forms an unsaturated carbonyl as the final product instead of an aldol. The …
This lesson delves into the aldol condensation catalyzed by bases, where aldols undergo dehydration to enals. As shown in Figure 1, the β-hydroxy …
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. …
Intramolecular aldol reaction occurs in dicarbonyl compounds such as dialdehydes, diketones, and keto-aldehydes. The dicarbonyl compounds possess more …
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 …
Crossed aldol addition is the reaction between two different carbonyl compounds under acidic or basic conditions. Here, both the carbonyl compounds …
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 …
Benzaldehyde, like formaldehyde, lacks an α hydrogen and cannot enolize to form an enolate. Hence, the reaction of benzaldehyde with a ketone in the …
The reaction between two different carbonyl compounds comprising α hydrogen in the presence of a strong base like lithium diisopropylamide (LDA) to …
The Knoevenagel condensation is an aldol-type reaction involving the condensation of aldehydes or ketones with active methylene compounds such as …
Regular Claisen condensation is a base-promoted reaction involving identical esters with two α hydrogens, condensing to produce β-ketoesters. It …
Regular Claisen condensation involves the synthesis of β-ketoesters by combining identical ester molecules bearing two α hydrogens in the …
Aldol condensation is an acid or base-catalyzed condensation between aldehydes or ketones to give an α,ꞵ-unsaturated carbonyl compound. A …
Dieckmann cyclization is an intramolecular Claisen condensation of diesters. The reaction occurs in the presence of a base and generates a cyclic …
Crossed Claisen condensations are base-promoted reactions between two different ester molecules producing β-dicarbonyl compounds. The reaction …
Ketones with α protons are deprotonated by strong bases like lithium diisopropylamide (LDA) to form enolate ions. The anion is stabilized by …
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 …
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 …
Malonic ester synthesis is a method to obtain α substituted carboxylic acids from ꞵ-diesters such as diethyl malonate and alkyl halides.
The …
α,β-Unsaturated carbonyl compounds are molecules bearing a carbonyl and alkene functionality in conjugation with each other. The conjugation in …
α,β-Unsaturated carbonyl compounds with two electrophilic sites, the carbonyl carbon, and the β carbon, are susceptible to nucleophilic …
The attack of a nucleophile at the β carbon of an α,β-unsaturated carbonyl compound is called conjugate addition. Conjugate addition …
Robinson annulation is a base-catalyzed reaction for the synthesis of 2-cyclohexenone derivatives from 1,3-dicarbonyl donors (such as cyclic diketones, …
α-Substituted ketones or aldehydes can be synthesized from enamines by the Stork enamine reaction, named after its pioneer Gilbert Stork. Enamines …
The Cannizzaro reaction is a base-promoted redox reaction producing a primary alcohol and a carboxylic acid from two molecules of a nonenolizable …
Indoxyl glycosides proved to be valuable and versatile tools for monitoring glycosidase activities. Indoxyls are released by enzymatic hydrolysis and are …
Methine-bridged conjugated bicyclic aromatic compounds are common constituents of a range of biologically relevant molecules such as porphyrins, …
The development of chemically recyclable biopolymers offers opportunities within the pursuit of a circular economy. Chemically recyclable biopolymers make …