Mixed Claisen condensation

Mixed Claisen condensations are analogous to mixed aldol condensations and involve carbon-carbon bond formation between the a carbon atom of one ester and the carbonyl carbon of another... 

The following equation shows an example of a mixed Claisen condensation m which a benzoate ester is used as the nonenohzable component... 

Give the structure of the product obtained when ethyl phenyl acetat C6H CH2C02CH2CH3) is treated with each of the following esters under conditions of the mixed Claisen condensation... 

In a reaction related to the mixed Claisen condensation nonenolizable esters are used as acylatmg agents for ketone enolates Ketones (via their enolates) are converted to p keto esters by reaction with diethyl carbonate... 

Mixed Claisen condensations (Section 21.3) Diethyl carbonate, diethyl oxalate, ethyl formate, and benzoate esters cannot form ester enolates but can act as acylating agents toward other ester enolates. 

The mixed Claisen condensation of two different esters is similar to the mixed aldol condensation of two different aldehydes or ketones (Section 23.5). Mixed Claisen reactions are successful only when one of the two ester components has no a hydrogens and thus can t form an enolate ion. For example, ethyl benzoate and ethyl formate can t form enolate ions and thus can t serve as donors. They can, however, act as the electrophilic acceptor components in reactions with other ester anions to give mixed /3-keto ester products. 

Mixed Claisen-like reactions can also be carried out between an ester and a ketone, resulting in the synthesis of a jS-diketone. The reaction works best when the ester component has no a hydrogens and thus can t act as the nucleophilic donor. For example, ethyl formate gives high yields in mixed Claisen condensations with ketones. 

Predicting the Product of a Mixed Claisen Condensation Reaction... 

Mixed Claisen condensations (Section 23.8) also occur frequently in living organisms, particularly in the pathway for fatty-acid biosynthesis that we ll discuss in Section 29.4. Butyryl synthase, for instance, reacts with malonvl ACP in a mixed Claisen condensation to give 3-ketohexanoyl ACP. 

The Claisen reaction is a carbonyl condensation that occurs between two ester molecules and gives a /3-keto ester product. Mixed Claisen condensations... 

Ethyl benzoate, mixed Claisen condensation reaction of, 890-891... 

Microwaves, electromagnetic spectrum and. 419 Mincralocorticoid, 1083 Minor groove (DNA), 1104-1105 Mitomycin C, structure of, 970 Mixed aldol reaction, 885-886 requirements for. 885-886 Mixed Claisen condensation reaction, 890-891... 

In a Claisen condensation the carbanion-enolate of an ester adds to the C=0 group of its parent ester. The addition is followed by loss of the OR group of the ester to give a -ketoester. In a mixed Claisen condensation the carbanion-enolate adds to the C=0 group of a molecule other than its parent. 

In these Claisen condensations OCjH, is displaced from the COOCjH, group by the a-carbanion formed from another ester molecule. Mixed Claisen condensations are feasible only if one of the esters has no a H. 

In the Claisen condensation the bond formed is between the carbonyl C and the C that is a to COOR. Work backwards by breaking this C—C bond and adding OR to the carbonyl C and adding H to the other C. Mixed Claisens are practical if one ester has no a H. 

---