Claisen Condensation Reactions Looking for organic chemistry practice problems? Here are a bunch of examples of reactions taken straight from the literature, ranging from easy to hard. Predict the products and practice your mechanisms! You'll learn better by only checking your answers after attempting 3-5 problems. Claisen condensation of two acetyl-CoA molecules to form acetoacetyl-CoA plus free CoASH (Scheme 1). 1.1 Two reactions: one fold Two main classes of Claisen condensations for carbon-carbon Another important aspect of the Claisen condensation is that the base portion used must be the same as the alcohol portion of the ester. If aqueous sodium hydroxide is used, irreversible ester hydrolysis will be the predominant reaction pathway. But if sodium ethoxide is used we simply get an identity reaction. The ethoxide attacks the Claisen condensation reactions are performed by enzymes that are members of the thiolase superfamily based on a three-dimensional fold first characterized in a degradative thiolase from Saccharomyces cerevisiae. 1,2 These enzymes primarily form dimers, with each subunit sharing a common superfamily topology, 3 whereas tetramers are observed only in the biosynthetic thiolase subfamily. 4 The Lecture #22: Claisen Condensation Esters also have split personality disorders → can be used either as an electrophile or a nucleophile Homo-Claisen condensation reaction: Similar to the aldol reaction One half of the molecules will act as the E+ and one half of the molecules will act as the Nu Except it is done with esters, it produces the beta-keto-ester and you CANNOT use NaOH in the ± The condensation of an aromatic aldehyde with an aliphatic aldehyde or ketone in the presence of a base or an acid to form an α,β-unsaturated aldehyde or ketone with high chemoselectivity is generally known as Claisen-Schmidt condensation. This reaction has been applied to the preparation of chalcone, flavanone, 1,3-diarylpropane The Claisen-Schmidt condensation reaction is an organic reaction in which a ketone or an aldehyde holding an α-hydrogen reacts with an aromatic carbonyl compound which does not have any α-hydrogens. This reaction is named after the chemists J.G. Schmidt and Rainer Ludwig Claisen. It can be noted that dibenzalacetone can be synthesized with Highlights : Tandem Cyclization/ Claisen Rearrangements, Primary Thioamides Microwave Chemistry Highlights : Tandem Claisen-Mislow-Evans Rearrangement, 1-Amido-2-cyclohexenes, 2-Aminoimidazoles, Suzuki/Aldol Condensation Reaction Doris Dallinger 15 The Claisen Condensation: A Synthesis of β-Keto Esters: In a Claisen condensation, the enolate of one ester molecule adds to the carbonyl group of another, resulting in an acyl substitution reaction that forms a b-keto ester and an alcohol molecule. The alcohol molecule that is formed derives from the alkoxyl group of the ester. The product in the Claisen condensation is a β-keto ester, and for the aldol addition, it is a β-hydroxy carbonyl. The main difference in the products is that, in Claisen reaction, both molecules retain their carbonyl group, and this is due to the presence of the alkoxy group which serves as a leaving group after the nucleophilic addition Claisen condensation Named after Rainer Ludwig Claisen Reaction type Coupling reaction Identifiers Organic Chemistry Portal claisen-condensation RSC ontology ID RXNO:0000043 The Claisen condensation (PDF). Organic Syntheses. 30: 18.; Collective Volume, 4,