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Chapter 13 α -Substitution and Condensations of Enols and Enolate

Chapter 13 α -Substitution and Condensations of Enols and Enolate. Text 1: Chapter 22, p 1003-1056 Text 2: 11,13 章. 13.1 Enols and enolate ions （烯醇和烯醇负离子）. Resonance-stabilized anion. Keto form ( 酮式， Stable). Enol form ( 烯醇式， unstable). 烯醇阴离子， Enolate ion. Resonance-stabilized cation.

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Chapter 13 α -Substitution and Condensations of Enols and Enolate

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  1. Chapter 13α-Substitution and Condensations of Enols and Enolate Text 1: Chapter 22, p 1003-1056 Text 2: 11,13章

  2. 13.1 Enols and enolate ions （烯醇和烯醇负离子） Resonance-stabilized anion Keto form (酮式，Stable) Enol form (烯醇式，unstable) 烯醇阴离子，Enolate ion Resonance-stabilized cation Enol form (烯醇式， unstable) Keto form (酮式， Stable) Keto and enol tautomers (酮和烯醇互变异构体）

  3. Keto and enol tautomers (酮和烯醇互变异构体） (S) (S) (R) Racemization( 外消旋作用)

  4. α-Substitution (α-取代) • α-halogenation • α-alkylation

  5. 13.2 α-Halogenation of ketones and aldehydes • Base-promoted α-halogenation In many cases, base-promoted halogenation does not stop with replacement of just one hydrogen. The product (α-haloketone) is more reactive toward further halogenation than is the starting material. 碱促进的卤代很难停止在单取代产物。卤代酮更容易发生进一步卤代。

  6. Reactivity of α-H under basic condition: Why ? Less stable More stable

  7. haloform（卤仿） bromoform（溴仿） iodoform（碘仿） yellow precipitate (黄色沉淀) The haloform reaction 卤仿反应 The iodoform test (碘仿试验)

  8. The mechanism of the haloform reaction

  9. Iodoform can test the stuctures of –COCH3 or–CHOHCH3 碘仿反应可以用来检验分子中是否存在甲基酮或乙醇结构。

  10. Acid-catalyzed α-halogenation Acidic halogenation can selectively replace just one hydrongen or more than one if appropreate amounts of the halogen are used.ition. 酸性条件下的卤代反应可以控制在一取代，或通过加卤素的量而控制得多取代产物。

  11. Reactivity of α-H under acidic condition: More stable Less stable 解释：取代基的超共轭效应

  12. How about aldehydes?

  13. 13.3 α-Bromogenation of carboxylic acids The Hell-Volhard-Zelinsky (HVZ) reaction 赫尔-乌尔哈-泽林斯基反应

  14. 13.4 α-alkylation （α烷基化） 1. Alkylation of enolate ions (烯醇负离子的烷基化) C- alkylation O- alkylation more common less common

  15. Base: Strong base, but weak nucleophile LDA (lithium diisopropylamide, 二异丙基氨基锂) C4H10 (i-C3H7)2NH -CHCO- ROH HOH pKa: >40 40 20 16~18 15

  16. LDA优先与位阻小的H反应。

  17. 2. Formation and alkylation of enamine : The Stork reaction δ- δ- δ-

  18. Alkylation烷基化 β-diketone, useful intermediate β-二酮，重要的合成中间体 Acylation酰基化

  19. 1,4-dicarbonyl compound 1，4-二羰基化合物 Problem: synthesis with two methods. • Hint: • LDA • The Stork reaction

  20. Condensation (缩合) • The Aldol reaction (羟醛缩合反应) • The Perkin reaction (珀金反应) • The ester condenstion (酯缩合反应) • Synthesis using β-dicarboyl compounds • Conjugate additions (共轭加成): the Michael reaction • The Robinson annulation (罗宾逊增环反应)

  21. 13.5 The aldol condensation 13.5 The aldol condensation 羟醛缩合反应；醛醇缩合反应 1. Base-catalyzed aldol condensation base: NaOH, NaOR

  22. Mechanism of the base-catalyzed aldol reaction aldol product β-hydroxy aldehyde β-羟基醛

  23. Base-catalyzed dehydration of aldol product α,β-unsaturated aldehyde α, β-不饱和醛

  24. 2. Acid-catalyzed aldol condensation How about the mechanism of the acid-catalyzed hydration of the aldol product?

  25. Problems: Synthetic applications 1. CH3CH=CHCH2OH 2. CH3CH2CH2CH2OH

  26. 3. Crossed Aldol condensations交错羟醛缩合反应

  27. Aldol Cyclizations （经羟醛缩合环化作用） To make 5- and 6-membered rings. Less hindered carbonyl group is attacked prefered. 位阻小的羰基优先被进攻。

  28. Problems: predict products.

  29. Problem: Show how each compound can be dissected into reagents joined by an aldol condensation, then decide wether the necessary alsol condensation is feasible.

  30. Problem: Show how to accomplish the following syntheses.

  31. 13.6 The Claisen ester condensation (克莱森酯缩合) 13.6 The Claisen ester condensation (克莱森酯缩合) pKa : ~24, less acidic than ketones and aldehydes (pKa~20)

  32. Mechanism of ester condensation 酯缩合机理 β-keto ester（ β-酮酸酯） Base: NaOC2H5, not NaOCH3，or NaOH, Why?

  33. 乙酰乙酸乙酯 Self-condensation, 自缩合

  34. The Dieckmann condensation ——a Claisen cyclization

  35. Crossed Claisen condensations 交叉克莱森缩合

  36. Crossed Claisen condensation between ketones and esters β-diketone（ β-二酮） β-keto ester（ β-酮酸酯） diketo ester（ 二酮酸酯）

  37. 13.7 Synthesis using β-carbonyl compounds(β-二羰基化合物在合成中的应用) 丙二酸二乙酯 乙酰乙酸乙酯 pKa1: 13 11 15.7(H2O ) 16(EtOH)

  38. The Malonic ester synthesis:----- Synthesis of substituted acetic acids mono- substituted acetic acids 单取代乙酸 Decarboxylation (脱羧)

  39. Decarboxylation (脱羧)

  40. di- substituted acetic acids 二取代乙酸

  41. Temporary ester group Problem: target molecule:

  42. The acetoacetic ester synthesis: -----Synthesis of substituted acetones Temporary ester group

  43. For example: The target molecule:

  44. 酮式分解 酸式分解

  45. Why?

  46. Problem: target molecule:

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