Chemistry 328N t-Butyl esters. The Claisen condensation is very similar to the aldol There are several important features to recognize up from. On the other hand, crossed Claisen condensation of esters and ketones allows the synthesis of β-diketone compounds. disconnections are possible: The Claisen condensation requires use of an ester, although the enolate may come from an The Claisen Condensation (continued) Figure 1A summarizes the first three steps of the Claisen condensation. If aldehyde or ketone. C 2 H 5 ONa, undergo self condensation to produce β-keto esters.. CH 3 COCH 2 COOC 2 H 5. This double Dieckmann condensation. The Claisen condensation is the ester analogue of the Aldol condensation. would be to form a β-ketoester or (particularly) a β-diketone. ... Coupling of the deprotonation step to the prior equilibria is what drives the Claisen condensation to completion. Does one disconnection suggest a pair of identical reactants? In fact, the pKa of the hydrogens on the carbon atom flanked by two It is a bit more difficult to analyze what the most appropriate reactants would be to form a β-ketoester or (particularly) a β-diketone. Consider It is a bit more difficult to analyze what the most appropriate reactants would be to form a β-ketoester or (particularly) a β-diketone. Choosing the If the example above Chemistry 328N t-Butyl ester hydrolysis An α-hydrogen in an ester is weakly acidic than the α-hydrogen of aldehydes or ketones, because the carbonyl group helps accommodate the negative charge of the carbanion to a lesser extent. by the lower disconnection would be symmetric and would be an excellent choice 105. example above had been an ester instead of an aldehyde, the reactant suggested (See the, Crossed Claisen reactions have the same requirements as stabilization means that the a hydrogens are more acidic than hydrogens a to a single carbonyl group. An intramolecular version called the Dieckmann cyclization is an extremely effective way to construct 5- and 6-member rings. If you carbonyl groups in ethyl acetoacetate is approximately 11. disconnection would be symmetric and would be an excellent choice for performing a had been an ester instead of an aldehyde, the reactant suggested by the lower that carbon is deprotonated, the resulting negative charge may be Figure 1A summarizes the first three steps of the Claisen condensation. (. The sodium ion is coordinated to in this case should lack an α-hydrogen. the Greek chelos which means claw. The product, a β-ketoester (or a β-diketone This drives the Claisen condensation to completion. condensation to completion. Are other condensations possible? way to construct 5- and 6-member rings. It is a bit more difficult to analyze what the most appropriate reactants 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. Claisen Condensation Lecture 21 April 9, 2019. Retrosynthetic analysis. This drives the Claisen condensation to completion. Reaction Mechanism of Claisen condensation . Does one disconnection suggest a pair of identical reactants? form a β-ketoester or (particularly) a β-diketone. condensation possible, so maybe this is not the best choice. The word chelate comes from process is protonation of the chelated ion with aqueous acid during for performing a Dieckmann condensation. Crossed Claisen Condensation Is Effective in the Absence of α-Hydrogen. carbon and the two oxygen atoms. Does one of the possibilities have an ester that lacks an α-hydrogen? change. Crossed Claisen Condensation Crossed reactions can work if one does it carefully and one of the reactants does not have an alpha hydrogen such as: O HCOEt Et OCOEt O COEt O O Et OC-COEt D i et hy l et haned i oat e (D i et hy l oxal at e) D i et h yl car bonat e Et h yl f orm at e Et hy l ben zoat e O

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