Ch. 22 - Conjugated Systems II: Pericyclic Reactions

Mullins - Organic Chemistry: A Learner Centered Approach 1st Edition

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Ch. 22 - Conjugated Systems II: Pericyclic Reactions

Problem 41c

Chapter 21, Problem 41c

Predict the product of the Claisen reactions shown.
(c)

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Identify the reactants involved in the Claisen reaction. Typically, a Claisen condensation involves two ester molecules or an ester and a ketone.

Determine the base used in the reaction. Commonly, a strong base like sodium ethoxide (NaOEt) is used to deprotonate the alpha hydrogen of the ester.

Recognize the formation of the enolate ion. The base abstracts an alpha hydrogen from the ester, forming an enolate ion, which is a key intermediate in the Claisen condensation.

Consider the nucleophilic attack. The enolate ion acts as a nucleophile and attacks the carbonyl carbon of another ester molecule, leading to the formation of a tetrahedral intermediate.

Identify the final product. The tetrahedral intermediate collapses, resulting in the elimination of an alkoxide ion and forming a β-keto ester as the final product of the Claisen condensation.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Claisen Condensation

Claisen condensation is a reaction where two esters or one ester and a ketone react in the presence of a strong base to form a β-keto ester or a β-diketone. The reaction involves the formation of an enolate ion from one of the ester molecules, which then attacks the carbonyl carbon of another ester, leading to the formation of a new carbon-carbon bond.

Enolate Ion Formation

Enolate ions are formed when a strong base deprotonates the α-hydrogen of an ester or ketone, resulting in a resonance-stabilized anion. This ion is nucleophilic and can attack electrophilic centers, such as the carbonyl carbon in Claisen condensation, facilitating the formation of new carbon-carbon bonds.

Product Prediction in Claisen Reaction

Predicting the product of a Claisen reaction involves identifying the nucleophilic enolate ion and the electrophilic carbonyl carbon. The enolate ion attacks the carbonyl carbon, forming a new C-C bond and resulting in a β-keto ester or β-diketone. Understanding the structure of reactants and the mechanism helps in predicting the final product accurately.

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Related Practice

Textbook Question

Predict the product of the Claisen reactions shown.

(b)

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Textbook Question

Predict the product of the following reactions. [When all of the reactions from this chapter are shown together, you must first decide which type of reaction each is. Is it a Diels–Alder, an electrocyclic, or a sigmatropic rearrangement? Drawing the product will be easier once this determination is made.]

(b)

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Textbook Question

Suggest a diene and a dienophile that would give the following products.

(c)

(a)