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Ch. 22 - Conjugated Systems II: Pericyclic Reactions
Mullins - Organic Chemistry: A Learner Centered Approach 1st Edition
Mullins1st EditionOrganic Chemistry: A Learner Centered ApproachISBN: 9780137566471Not the one you use?Change textbook
All textbooksMullins 1st EditionCh. 22 - Conjugated Systems II: Pericyclic ReactionsProblem 53
Chapter 21, Problem 53

The Ireland–Claisen reaction is a variant of the Claisen reaction studied in this chapter.
(a) Suggest a mechanism for the first step.
(b) Predict the product (B) that would result from heating intermediate A.
(c) Hydrolysis of B gives a carboxylic acid.
Suggest a mechanism for this reaction.
Chemical reaction mechanism diagram illustrating the Ireland–Claisen reaction with labeled steps and intermediates.

Verified step by step guidance
1
The first step involves the deprotonation of the alpha hydrogen of the ester by LDA (Lithium diisopropylamide), a strong base, to form an enolate ion. This is a common step in reactions involving carbonyl compounds to generate nucleophilic enolates.
The enolate ion then reacts with trimethylsilyl chloride (Me3SiCl) to form a silyl enol ether. This step involves the nucleophilic attack of the enolate oxygen on the silicon atom, resulting in the formation of intermediate A.
Upon heating, intermediate A undergoes a [3,3]-sigmatropic rearrangement, known as the Ireland–Claisen rearrangement. This rearrangement involves the migration of the allyl group to the oxygen atom, forming a new carbon-carbon bond and resulting in the formation of product B.
The product B, which is an ester, undergoes hydrolysis in the presence of an acid (H3O+). This involves the nucleophilic attack of water on the carbonyl carbon, followed by proton transfers and the elimination of an alcohol, leading to the formation of a carboxylic acid.
The final product of the hydrolysis is a carboxylic acid, which is formed by the cleavage of the ester linkage in product B. This step completes the transformation of the initial ester into a carboxylic acid.

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Key Concepts

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

Ireland–Claisen Rearrangement

The Ireland–Claisen rearrangement is a variant of the Claisen rearrangement involving silyl enol ethers. It typically involves the conversion of an allyl ester to a γ,δ-unsaturated carboxylic acid. The reaction proceeds through a six-membered cyclic transition state, allowing for the migration of the allyl group and formation of a new carbon-carbon bond.
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Definition of Claisen Rearrangement

Silyl Enol Ether Formation

Silyl enol ethers are formed by the reaction of enolates with silyl chlorides, such as trimethylsilyl chloride (Me3SiCl). In the Ireland–Claisen rearrangement, lithium diisopropylamide (LDA) is used to generate the enolate, which then reacts with Me3SiCl to form the silyl enol ether. This intermediate is crucial for the rearrangement process, as it stabilizes the enolate and facilitates the subsequent rearrangement.
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Hydrolysis of Esters

Hydrolysis of esters involves the conversion of an ester into a carboxylic acid and an alcohol, typically under acidic or basic conditions. In the context of the Ireland–Claisen rearrangement, the hydrolysis of the rearranged product (B) leads to the formation of a carboxylic acid. Acidic hydrolysis involves protonation of the ester, followed by nucleophilic attack by water, leading to the cleavage of the ester bond and formation of the carboxylic acid.
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Related Practice
Textbook Question

The [2 + 2] cyclization is especially useful when done intramolecularly. 

(a) What makes intramolecular reactions more favorable? 

(b) Predict the product of the following cyclization (slight modification of a reaction from Angew. Chem. 2011, 50, 5149)

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Textbook Question

The Claisen rearrangement can be used to attach allyl groups to benzene via initial alkylation of a phenol.

(a) Predict the identity of A and B

(b) provide an arrow-pushing mechanism for each step. [The phenol alkylation is simply a Williamson ether synthesis reaction.]


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Textbook Question

Only after working Assessment 22.53, predict the product of the following reactions.

(b)

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Textbook Question

By forming a Lewis acid–Lewis base complex with the dienophile, Lewis acids are able to increase the rate of Diels–Alder reactions. Why might this be true?

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Textbook Question

Only after working Assessment 22.53, predict the product of the following reactions.

(a)

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Textbook Question

The Johnson–Claisen reaction is a variant of the Claisen reaction studied in this chapter. (a) Suggest a mechanism for the first step. (b) Predict the product (B) that would result from heating intermediate A.

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