Claisen Adapter
Claisen Adapter - Related Videos
01:33
Aldol Condensation vs Claisen Condensation
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2025
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.
01:08
Esters to β-Ketoesters: Claisen Condensation Mechanism
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2025
Regular Claisen condensation involves the synthesis of β-ketoesters by combining identical ester molecules bearing two α hydrogens in the presence of an alkoxide base. The reaction commences with the deprotonation of the acidic α hydrogen by the base to form a resonance stabilized ester enolate. This nucleophilic ion then attacks the carbonyl center of another ester molecule to generate a tetrahedral alkoxide intermediate. Next, the expulsion of the alkoxide group from the intermediate restores...
01:24
Esters to β-Ketoesters: Claisen Condensation Overview
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2023
Regular Claisen condensation is a base-promoted reaction involving identical esters with two α hydrogens, condensing to produce β-ketoesters. It is a nucleophilic acyl substitution reaction wherein one of the ester molecules, upon deprotonation by the base, forms a nucleophilic enolate ion, while the other molecule serves as an electrophile. The condensation reaction requires specific nonaqueous bases, such as alkoxide, which must be similar to the alkoxy group of the ester molecule. The use...
01:18
β-Dicarbonyl Compounds via Crossed Claisen Condensations
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2025
Crossed Claisen condensations are base-promoted reactions between two different ester molecules producing β-dicarbonyl compounds. The reaction involving esters, with both containing α hydrogen, results in a mixture of four different products that are difficult to isolate. This reduces the synthetic utility of the reaction. This problem is resolved by using one of the esters without any α hydrogen, such as aryl esters. Additionally, highly reactive molecules like formate esters serve as...
01:01
Ketones with Nonenolizable Aromatic Aldehydes: Claisen–Schmidt Condensation
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2023
Benzaldehyde, like formaldehyde, lacks an α hydrogen and cannot enolize to form an enolate. Hence, the reaction of benzaldehyde with a ketone in the presence of an aqueous base forms a single crossed product. This reaction is referred to as Claisen–Schmidt condensation. As the self-condensation of ketones is generally not favored in basic conditions, the self-condensed products do not form in the reaction between ketones and benzaldehyde. The general reaction of Claisen–Schmidt condensation is...
FAQs
Heating supplies the energy needed for the rearrangement to proceed through a concerted, six-electron [3,3]-sigmatropic pathway. In this process, bond reorganization occurs through a cyclic transition state rather than through separately formed ionic or radical intermediates. The result is a reorganized carbonyl compound with a changed carbon framework, making thermal activation central to the adapter’s function.
The cyclic transition state brings the allyl and unsaturated portions of the framework into the arrangement required for simultaneous bond changes. This organized pathway helps convert the starting connectivity into a new carbon skeleton while forming a carbon-carbon bond. Because the structural relationships are maintained during the rearrangement, the adapter can carry information about substituent arrangement into the product.
Substituent placement and stereochemistry determine how structural information is organized within the adapter before rearrangement. When the framework is designed appropriately, those features can be transferred to the reorganized carbonyl product. This control supports stereoselective synthesis, allowing chemists to create products with defined three-dimensional relationships rather than treating carbon-skeleton formation as an uncontrolled rearrangement.
Design must account for how the allyl group and vinyl ether or related unsaturated component are positioned within the functionalized framework. Their arrangement must support the cyclic transition state required for the [3,3]-sigmatropic process. Substituent placement also matters because it influences the structural information available for transfer into the carbonyl-containing product.
These adapters provide a strategy for reorganizing carbon skeletons while forming carbon-carbon bonds in a single rearrangement step. That combination can support chain extension and the construction of more elaborate molecular frameworks. The approach is therefore useful when a synthesis requires efficient connectivity changes rather than assembling every new bond through separate transformations.
Their applications include stereoselective synthesis and the preparation of complex natural products and pharmaceutical intermediates. In these settings, the adapter helps organize unsaturated components so the rearrangement can generate a new carbon framework and carbonyl compound. Its value comes from combining structural reorganization, bond formation, and transfer of stereochemical information within one synthetic strategy.