Name: &amp;#946;-Dicarbonyl Compounds via Crossed Claisen Condensations
Uploaded: 2023-04-30T10:25:05
Description: Learn by watching this video about β-Dicarbonyl Compounds via Crossed Claisen Condensations at JoVE.com

Claisen condensation between two different esters is termed crossed Claisen condensation.
If both esters contain &#945; hydrogens, then four different types of &#42933;-ketoesters are formed. Of these, two are self-condensation products and the other two are crossed-condensation products.
A successful crossed Claisen condensation requires at least one ester molecule with no &#945; hydrogen or the use of LDA base.
For instance, aryl esters have no &#945; hydrogen and, therefore, cannot form enolates. They give crossed Claisen condensation products with other enolate-forming ester molecules.
Formate esters, in addition to containing no &#945; hydrogen, are highly reactive compared to other esters, making them suitable for crossed Claisen condensation.
If a less reactive, no &#945;-hydrogen-containing&#160;ester is used, an excess of it is required for a feasible reaction.
If &#945;-hydrogen-containing esters are used, then a strong base like LDA facilitates a directed crossed Claisen condensation&#160;by generating an irreversible ester enolate, followed by its reaction with another ester molecule.

&beta;-dicarbonyl compounds via crossed claisen condensations

Crossed Claisen condensations are base-promoted reactions between two different ester molecules producing &#946;-dicarbonyl compounds.&#160; The reaction involving esters, with both containing &#945; hydrogen, results in a mixture of four different products that are difficult to isolate. This reduces the synthetic utility of the reaction.
<img alt="Figure1" src="/files/ftp_upload/12392/12392_Figure_1.svg" style="text-align: center; height: 225px;" />
This problem is resolved by using one of the esters without any &#945; hydrogen, such as aryl esters.
<img alt="Figure2" src="/files/ftp_upload/12392/12392_Figure_2.svg" style="text-align: center; height: 55px;" />
Additionally, highly reactive molecules like formate esters serve as effective electrophilic partners in cross Claisen condensation.
<img alt="Figure3" src="/files/ftp_upload/12392/12392_Figure_3.svg" style="text-align: center; height: 70px;" />
Similarly, less reactive esters with no &#945; protons make the reaction feasible when present in excess quantity.
<img alt="Figure4" src="/files/ftp_upload/12392/12392_Figure_4.svg" style="text-align: center; height: 90px;" />
Another approach to obtain an efficient cross Claisen condensation is the use of a strong, sterically hindered base&#8212;LDA. It irreversibly deprotonates one of the esters to enolate, while the other ester acts as an electrophile.
<img alt="Figure5" src="/files/ftp_upload/12392/12392_Figure_5.svg" style="text-align: center; height: 75px;" />
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 &#42933;-dicarbonyl compounds.
<img alt="Figure6" src="/files/ftp_upload/12392/12392_Figure_6.svg" style="text-align: center; height: 85px;" />

Learn by watching this video about β-Dicarbonyl Compounds via Crossed Claisen Condensations at JoVE.com

&amp;#946;-Dicarbonyl Compounds via Crossed Claisen Condensations

&beta;-Dicarbonyl Compounds via Crossed Claisen Condensations

Crossed Claisen condensations are base-promoted reactions between two different ester molecules producing &#946;-dicarbonyl compounds.&#160; The reaction ...