Textbook Question
Show how crossed Claisen condensations could be used to prepare the following esters.
(b)
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Ch. 22 - Condensations and Alpha Substitutions of Carbonyl Compounds
Wade9th EditionOrganic ChemistryISBN: 9780135213728
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Table of contents
- Ch.1 - Structure and Bonding107
- Ch. 2 - Acids and Bases; Functional Groups115
- Ch.3 - Structure and Stereochemistry of Alkanes100
- Ch.4 - The Study of Chemical Reactions99
- Ch.5 - Stereochemistry93
- Ch.6 - Alkyl Halides; Nucleophilic Substitution118
- Ch. 7 - Structure and Synthesis of Alkenes; Elimination158
- Ch.8 - Reactions of Alkenes171
- Ch.9 - Alkynes91
- Ch.10 - Structure and Synthesis of Alcohols143
- Ch.11 - Reactions of Alcohols104
- Ch. 12 - Infrared Spectroscopy and Mass Spectrometry22
- Ch. 13 - Nuclear Magnetic Resonance Spectroscopy45
- Ch. 14 - Ethers, Epoxides, and Thioethers72
- Ch. 15 - Conjugated Systems, Orbital Symmetry, and Ultraviolet Spectroscopy89
- Ch. 16 - Aromatic Compounds74
- Ch. 17 - Reactions of Aromatic Compounds126
- Ch. 18 - Ketones and Aldehydes193
- Ch. 19 - Amines129
- Ch. 20 - Carboxylic Acids77
- Ch. 21 - Carboxylic Acid Derivatives141
- Ch. 22 - Condensations and Alpha Substitutions of Carbonyl Compounds175
- Ch. 23 - Carbohydrates and Nucleic Acids93
- Ch. 24 - Amino Acids, Peptides, and Proteins54
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Wade 9th EditionCh. 22 - Condensations and Alpha Substitutions of Carbonyl CompoundsProblem 42c,d
Wade 9th EditionCh. 22 - Condensations and Alpha Substitutions of Carbonyl CompoundsProblem 42c,dChapter 22, Problem 42c,d
Predict the products from crossed Claisen condensation of the following pairs of esters. Indicate which combinations are poor choices for crossed Claisen condensations.
(c) 
(d) 
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Identify the esters involved in the crossed Claisen condensation. In a crossed Claisen condensation, two different esters react in the presence of a strong base to form a β-keto ester.
Determine the enolate ion that will form from each ester. The enolate ion is generated from the ester with the more acidic alpha hydrogen. Use the base to deprotonate the alpha hydrogen of the ester to form the enolate ion.
Consider the reactivity of each ester. Esters with no alpha hydrogens cannot form enolates and will act as electrophiles. Identify which ester will act as the nucleophile (enolate) and which will act as the electrophile.
Predict the product by combining the enolate ion with the carbonyl carbon of the electrophilic ester. This forms a new carbon-carbon bond, resulting in a β-keto ester.
Evaluate the choice of esters for the reaction. A poor choice for crossed Claisen condensation occurs when both esters can form enolates, leading to a mixture of products. Ideally, one ester should lack alpha hydrogens to avoid multiple products.
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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 between two esters or an ester and a carbonyl compound in the presence of a strong base, leading to the formation of a β-keto ester or a β-diketone. This reaction involves the nucleophilic attack of an enolate ion derived from one ester on the carbonyl carbon of another ester, followed by the elimination of an alcohol. Understanding this mechanism is crucial for predicting the products of crossed Claisen condensations.
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Claisen Condensation
Enolate Ion Formation
Enolate ions are formed when a strong base abstracts a proton from the α-carbon of an ester, resulting in a resonance-stabilized anion. The stability of the enolate ion is influenced by the substituents on the ester, which can affect the reactivity in the Claisen condensation. Recognizing how to generate and utilize enolate ions is essential for successfully predicting the outcomes of crossed Claisen reactions.
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Crossed Claisen Condensation Limitations
Crossed Claisen condensation can lead to multiple products, especially when using two different esters. Poor choices for this reaction typically involve esters that can both form enolates, leading to self-condensation rather than the desired crossed product. Identifying which ester combinations are likely to yield unwanted products is key to successfully predicting the outcomes of these reactions.
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Related Practice
Textbook Question
Some (but not all) of the following keto esters can be formed by Dieckmann condensations. Determine which ones are possible, and draw the starting diesters.
(c)
(d)
1298
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Textbook Question
Predict the products from crossed Claisen condensation of the following pairs of esters. Indicate which combinations are poor choices for crossed Claisen condensations.
(a)
(b)
883
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Textbook Question
Propose a mechanism for the crossed Claisen condensation between ethyl acetate and ethyl benzoate.
115
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Textbook Question
Show how crossed Claisen condensations could be used to prepare the following esters.
(c)
(d)
646
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Textbook Question
Show how crossed Claisen condensations could be used to prepare the following esters.
(a)
1001
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