15.30:

β-Dicarbonyl Compounds via Crossed Claisen Condensations

JoVE Core
Organic Chemistry
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JoVE Core Organic Chemistry
β-Dicarbonyl Compounds via Crossed Claisen Condensations

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01:18 min

April 30, 2023

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.

Figure1

This problem is resolved by using one of the esters without any α hydrogen, such as aryl esters.

Figure2

Additionally, highly reactive molecules like formate esters serve as effective electrophilic partners in cross Claisen condensation.

Figure3

Similarly, less reactive esters with no α protons make the reaction feasible when present in excess quantity.

Figure4

Another approach to obtain an efficient cross Claisen condensation is the use of a strong, sterically hindered base—LDA. It irreversibly deprotonates one of the esters to enolate, while the other ester acts as an electrophile.

Figure5

A variation of crossed Claisen condensation is the reaction of ketones with esters, wherein the enolate of ketone attacks the carbonyl center of the ester producing ꞵ-dicarbonyl compounds.

Figure6