Table of contents

1. A Review of General Chemistry5h 5m
2. Molecular Representations1h 14m
3. Acids and Bases2h 46m
4. Alkanes and Cycloalkanes4h 17m
5. Chirality3h 39m
6. Thermodynamics and Kinetics1h 22m
7. Substitution Reactions1h 48m
8. Elimination Reactions2h 30m
9. Alkenes and Alkynes2h 9m
10. Addition Reactions3h 19m
11. Radical Reactions1h 58m
12. Alcohols, Ethers, Epoxides and Thiols2h 42m
13. Alcohols and Carbonyl Compounds2h 17m
14. Synthetic Techniques1h 26m
15. Analytical Techniques:IR, NMR, Mass Spect7h 3m
16. Conjugated Systems6h 13m
17. Ultraviolet Spectroscopy51m
18. Aromaticity2h 34m
19. Reactions of Aromatics: EAS and Beyond5h 1m
20. Phenols55m
21. Aldehydes and Ketones: Nucleophilic Addition4h 56m
22. Carboxylic Acid Derivatives: NAS2h 51m
23. The Chemistry of Thioesters, Phophate Ester and Phosphate Anhydrides1h 10m
24. Enolate Chemistry: Reactions at the Alpha-Carbon1h 53m
25. Condensation Chemistry2h 9m
26. Amines1h 43m
27. Heterocycles2h 0m
28. Carbohydrates5h 53m
29. Amino Acids4h 20m
30. Peptides and Proteins2h 42m
31. Catalysis in Organic Reactions1h 30m
32. Lipids 2h 50m
33. The Organic Chemistry of Metabolic Pathways2h 52m
34. Nucleic Acids1h 32m
35. Transition Metals6h 14m
36. Synthetic Polymers1h 49m

16. Conjugated Systems

Claisen Rearrangement

Organic Chemistry

16. Conjugated Systems

Claisen Rearrangement

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Problem 52

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.]

Verified step by step guidance

Step 1: Begin with the phenol and treat it with sodium hydride (NaH), a strong base. This deprotonates the hydroxyl group, forming a phenoxide ion.

Step 2: The phenoxide ion then reacts with allyl bromide in a Williamson ether synthesis. The oxygen of the phenoxide ion attacks the carbon attached to the bromine, displacing the bromide ion and forming an allyl phenyl ether. This is compound A.

Step 3: Upon heating, the allyl phenyl ether undergoes a Claisen rearrangement. This involves a [3,3]-sigmatropic rearrangement where the allyl group migrates to the ortho position relative to the oxygen, forming an ortho-allyl phenol. This is compound B.

Step 4: The ortho-allyl phenol can tautomerize between its keto and enol forms. The keto form is a cyclohexenone, while the enol form is an ortho-allyl phenol.

Step 5: Provide an arrow-pushing mechanism for each step: (a) Deprotonation of phenol by NaH, (b) Nucleophilic attack of phenoxide on allyl bromide, (c) [3,3]-sigmatropic rearrangement in Claisen rearrangement, and (d) Keto-enol tautomerism.

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Key Concepts

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

Williamson Ether Synthesis

The Williamson ether synthesis is a reaction that forms an ether from an alkoxide ion and an alkyl halide. In this process, a phenol is deprotonated by a strong base like NaH to form a phenoxide ion, which then reacts with an allyl bromide to form an ether. This step is crucial for forming the intermediate that undergoes the Claisen rearrangement.

Claisen Rearrangement

The Claisen rearrangement is a pericyclic reaction where an allyl vinyl ether is converted into a γ,δ-unsaturated carbonyl compound upon heating. This rearrangement involves a [3,3]-sigmatropic shift, where the allyl group migrates to the ortho position of the aromatic ring, forming a ketone. It is a key step in attaching allyl groups to benzene derivatives.

Keto-Enol Tautomerism

Keto-enol tautomerism is an equilibrium between a ketone and its corresponding enol form. In this process, the ketone form, which is typically more stable, can convert to an enol form through the migration of a hydrogen atom and the shift of a double bond. This tautomerism is important for understanding the final structure of the product in the Claisen rearrangement.

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Related Practice

Textbook Question

Predict the product of the Claisen reactions shown.

(b)

Textbook Question

Propose a mechanism for the following reaction:

Textbook Question

If the terminal sp² carbon of the substituent attached to the benzene ring is labeled with ¹⁴C, where will the label be in the product?

Textbook Question

Draw the product of the following reaction:

Textbook Question

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.

Suggest a mechanism for this reaction.

Textbook Question

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

(a)

Textbook Question

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

(b)

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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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.]

Key Concepts

Williamson Ether Synthesis

Claisen Rearrangement

Keto-Enol Tautomerism

Watch next

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.]