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Ch. 17 - Reactions at the Alpha-Carbon
Bruice - Organic Chemistry 8th Edition
Bruice8th EditionOrganic ChemistryISBN: 9780135213711Not the one you use?Change textbook
All textbooksBruice 8th EditionCh. 17 - Reactions at the Alpha-CarbonProblem 66b
Chapter 18, Problem 66b

Indicate how each of the following compounds can be synthesized from the given starting material and any other necessary reagents:
b. Chemical structures showing the synthesis of a compound via Claisen condensation, with reactants and product labeled.

Verified step by step guidance
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Step 1: Analyze the starting material and the target compound. The starting material is a β-keto ester (ethyl acetoacetate), and the target compound is a bicyclic diketone. This suggests a reaction involving cyclization and formation of two new carbon-carbon bonds.
Step 2: Recognize that the transformation likely involves an intramolecular aldol condensation. This reaction requires the generation of an enolate ion from the β-keto ester under basic conditions, which will then attack another carbonyl group within the molecule.
Step 3: Treat the starting material with a strong base, such as sodium ethoxide (NaOEt), to deprotonate the α-hydrogen of the β-keto ester and form the enolate ion. The enolate ion is nucleophilic and can initiate the cyclization process.
Step 4: The enolate ion attacks the carbonyl group of the ester, forming a new carbon-carbon bond and creating a cyclic intermediate. This intermediate undergoes elimination of ethanol to form the bicyclic diketone structure.
Step 5: After the reaction is complete, the product can be isolated and purified using standard techniques such as recrystallization or chromatography to obtain the desired bicyclic diketone.

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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 on the carbonyl carbon of another ester, followed by the elimination of an alcohol. Understanding this mechanism is crucial for synthesizing complex cyclic structures from simpler precursors.
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Claisen Condensation

Enolate Ion Formation

Enolate ions are formed when a strong base abstracts a proton from the alpha carbon of a carbonyl compound, resulting in a resonance-stabilized anion. This species is a key intermediate in many organic reactions, including the Claisen condensation. Recognizing how to generate and utilize enolate ions is essential for predicting the outcomes of reactions involving carbonyl compounds.
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Formation of Enolates

Cyclization Reactions

Cyclization reactions involve the formation of cyclic compounds from acyclic precursors, often through intramolecular reactions. In the context of the Claisen condensation, cyclization can occur when the reaction leads to the formation of a ring structure, as seen in the provided reaction diagram. Understanding the conditions that favor cyclization, such as sterics and electronics, is important for successful synthesis.
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Related Practice
Textbook Question

The Reformatsky reaction is an addition reaction in which an organozinc reagent is used instead of a Grignard reagent to add to the carbonyl group of an aldehyde or a ketone. Because the organozinc reagent is less reactive than a Grignard reagent, a nucleophilic addition to the ester group does not occur.

The organozinc reagent is prepared by treating an α-bromo ester with zinc.

Describe how each of the following compounds can be prepared, using a Reformatsky reaction:

c.

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Textbook Question

The Reformatsky reaction is an addition reaction in which an organozinc reagent is used instead of a Grignard reagent to add to the carbonyl group of an aldehyde or a ketone. Because the organozinc reagent is less reactive than a Grignard reagent, a nucleophilic addition to the ester group does not occur. The organozinc reagent is prepared by treating an α-bromo ester with zinc.

Describe how each of the following compounds can be prepared, using a Reformatsky reaction:

a.

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Textbook Question

There are other condensation reactions similar to the aldol and Claisen condensations:

c. The Knoevenagel condensation is the condensation of an aldehyde or a ketone that has no a-hydrogens and a compound such as diethyl malonate that has an a-carbon flanked by two electron-withdrawing groups. Draw the product obtained from the following Knoevenagel condensation:

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Textbook Question

There are other condensation reactions similar to the aldol and Claisen condensations:

b. What compound is formed if water is added to the product of a Perkin condensation?

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Textbook Question

Indicate how each of the following compounds can be synthesized from the given starting material and any other necessary reagents:

c.

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Textbook Question

What product is obtained when the product of a Knoevenagel condensation is heated in an aqueous acidic solution?

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