Watch the recordings here on Youtube! You should look back at the general mechanism for a forward Claisen condensation and convince yourself that the retro-Claisen mechanism illustrated aboveis a step-by-step reverse process. A CYCLIC CLAISEN CONDENSATION NaOMe MeOH 42. The LibreTexts libraries are Powered by MindTouch® and are supported by the Department of Education Open Textbook Pilot Project, the UC Davis Office of the Provost, the UC Davis Library, the California State University Affordable Learning Solutions Program, and Merlot. Claisen rearrangement is an organic chemical reaction that offers a powerful method in the formation of carbon-carbon bonds.The reactant of this reaction – allyl vinyl ether, is converted into a gamma, delta-unsaturated carbonyl compound when subjected to heat or a Lewis acid.. The Claisen condensation reaction is an organic coupling reaction that results in the formation of a C-C bond between either a single ester and one carbonyl compoundor between two esters. Unless otherwise noted, LibreTexts content is licensed by CC BY-NC-SA 3.0. A typical nucleophilic acyl substitution reaction might have an alcohol nucleophile attacking a thioester, driving off a thiol and producing an ester. Other than that, the reaction looks just like the Claisen condensation reactions we saw earlier. Claisen condensation The formation of a beta-keto ester from two esters, one of which has an alpha-hydrogen atom; malate synthase, citrate synthase, and atp citrate lyase all catalyze such reactions. For more information contact us at email@example.com or check out our status page at https://status.libretexts.org. Propose a likely mechanism for the reaction shown. The product is a β-keto ester. In the next section, you will see how the range of β‑keto esters that can be prepared by this method is extended through the use of two different esters as starting materials. Explain. Esters with α-hydrogen atom on treatment with a strong base, e.g. Meanwhile, a transthioesterification reaction occurs (steps a and b) to free the enzyme's cysteine residue, regenerating a fatty acyl CoA molecule which is two carbons shorter than the starting substrate. Because esters can contain α hydrogens they can undergo a condensation reaction similar to the aldol reaction called a Claisen Condensation. For example, to deprotonate the ethyl acetate or any other ethyl ester, an … Claisen Condensation Lecture 21 April 9, 2019. Notice that, again, the electrophilic acyl group is first transferred to an active site cysteine, which then serves as the leaving group in the carbon-carbon bond forming process. And that is the alkoxide ion having the same alkyl group as the reacting esters. The enolate carbon attacks the electrophilic thioester carbon, forming a tetrahedral intermediate (step 2) which collapses to expel the cysteine thiol (step 3). Dr. Dietmar Kennepohl FCIC (Professor of Chemistry, Athabasca University), Prof. Steven Farmer (Sonoma State University). The leaving enolate reprotonates (step 3) to bring us back to where we started, with two separate thioesters. Claisen condensation is a fun reaction used to form a beta keto ester when reacting esters in a strong base. The retro-Claisen reaction (step IV) in fatty acid degradation. Chemistry 328N t-Butyl ester hydrolysis The Choice of Base in Claisen Condensation. In a step in the degradation if the amino acid, steps are hydrolytic, meaning that water, rather than a, that cleaves the carbon-carbon bond. When your body 'burns' fat to get energy, it is a retro-Claisen cleavage reaction (EC 22.214.171.124) that is responsible for breaking the carbon-carbon bonds in step IV of the fatty acid degradative pathway. (J. Biol. Claisen Condensation. If, however, the attacking nucleophile in an acyl substitution reaction is the a-carbon of an enolate, a new carbon-carbon bond is formed. Watch the recordings here on Youtube! Dieckmann Condensation: The addition of base to a 1,6-diester causes the diester to undergo intramolecular Claisen Condensation, thereby forming a five membered ring β-keto ester.