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

24. Enolate Chemistry: Reactions at the Alpha-Carbon

Enolate

Organic Chemistry

24. Enolate Chemistry: Reactions at the Alpha-Carbon

Enolate

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7:57 minutes

Problem 87a

Textbook Question

Alkylation of the following compound with methyl iodide under two different conditions forms two different ketoesters (A and B). Each ketoester forms a cyclic diketone (C and D) when treated with methoxide ion in methanol. a. Draw the structures of A and B, and indicate the conditions used in the alkylation reaction that cause that ketoester to be formed.

Verified step by step guidance

Step 1: Analyze the given compound and reaction conditions. The compound contains two carbonyl groups (a ketone and an ester), which are capable of undergoing enolate formation. The alkylation reaction involves methyl iodide (CH₃I) as the alkylating agent, and the enolate formation is controlled by the use of LDA (lithium diisopropylamide) in THF (tetrahydrofuran) at different temperatures.

Step 2: Understand the role of temperature in enolate formation. At -78°C, LDA selectively deprotonates the less sterically hindered alpha-carbon (kinetic enolate formation). At 0°C, LDA allows for equilibration, favoring the more stable enolate (thermodynamic enolate formation). This difference in enolate formation leads to the formation of two different ketoesters (A and B).

Step 3: For the reaction at -78°C (kinetic conditions), identify the alpha-carbon that is less sterically hindered. Deprotonation at this site forms the kinetic enolate, which reacts with methyl iodide to form ketoester A. Draw the structure of ketoester A, showing the methyl group added to the less hindered alpha-carbon.

Step 4: For the reaction at 0°C (thermodynamic conditions), identify the alpha-carbon that forms the more stable enolate. Deprotonation at this site forms the thermodynamic enolate, which reacts with methyl iodide to form ketoester B. Draw the structure of ketoester B, showing the methyl group added to the more stable alpha-carbon.

Step 5: When treated with methoxide ion in methanol, both ketoesters (A and B) undergo intramolecular aldol condensation to form cyclic diketones (C and D). Draw the structures of C and D, showing the cyclization and formation of the diketone products.

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Key Concepts

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

Alkylation Reaction

Alkylation is a chemical reaction that involves the transfer of an alkyl group from one molecule to another. In this context, the alkylation of a compound with methyl iodide (CH3I) occurs under different conditions, leading to the formation of distinct ketoesters. The choice of conditions, such as temperature and the base used, significantly influences the regioselectivity and outcome of the reaction.

Lithium Diisopropylamide (LDA)

LDA is a strong, non-nucleophilic base commonly used in organic synthesis to deprotonate compounds, generating enolates. The temperature at which LDA is used affects the stability and reactivity of the enolate formed. For instance, using LDA at -78°C leads to the formation of a more stable enolate, which can result in different alkylation products compared to using LDA at 0°C.

Cyclic Diketone Formation

Cyclic diketones are formed through the reaction of ketoesters with methoxide ions in methanol. This process typically involves nucleophilic attack by the methoxide on the carbonyl carbon of the ketoester, leading to the formation of a cyclic structure. The specific ketoester formed in the initial alkylation step determines the structure of the resulting cyclic diketone, highlighting the importance of the alkylation conditions.

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