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H
C
H
H
H
Synthesis
Biosynthesis
Reagents = small carbon-based molecules (e.g. amino acids, carbohydrates)
Catalysts = enzymes, proteins that bind and then catalyze chemical reaction
Chapter 17: Aldehydes and Ketones – Nucleophilic Addition
17.1 – Nomenclature of Aldehydes and Ketones
17.2 – 17.4 – Structure of C=O and Sources
17.5 – Nucleophilic Addition
Nucleophiles:
H2O – hydrates
H- from NaBH4 or LiAlH4
R- from RMgX, RLi
NC-, ROH, RNH2, R2NH
17.6 – Hydration of Aldehydes and Ketones
a
Hydrate Formation
(relevant to H2CrO4 oxidation)
Table 17.3
17.6 – Hydration of Aldehydes and Ketones
Electronic (how stable is the carbonyl – how positive is the carbon?)
Steric (how crowded does the hydrate become?)
Hydrate becomes more crowded, which effects the equilibrium with
the precursor aldehyde or ketone
17.6 – Hydration of Aldehydes and Ketones
Hydrate Formation is Base-Catalyzed
Reaction faster than just with water (pH 7)
Hydroxide is much more nucleophilic than water
Hydroxide regenerated in second step
17.6 – Hydration of Aldehydes and Ketones
17.6 – Hydration of Aldehydes and Ketones – Fig 17.5
17.6 – Hydration of Aldehydes and Ketones
Hydrate Formation is also Acid-Catalyzed
Reaction faster than just H2O, H+ regenerated in second step
17.7 – Cyanohydrin Formation
Both HCN and cyanide anion present in mixture
Cyanide anion catalyzes the reaction, adds to the C=O
New C-C bond formed (compare with Grignard)
17.8 – Acetal Formation
• Acid catalyzed, use TsOH for example
• Use excess ROH to drive equilibrium to the right
• Water is the byproduct
• Acetals are stable to bases and nucleophiles
• Use excess water and H+ to go back to carbonyl - mechanism
17.8 – Acetal Formation
Acetals do not react with bases or nucleophiles - useful
17.9 – Acetals as Protecting Groups
Possible solution:
17.9 – Acetals as Protecting Groups
17.9 – Acetals as Protecting Groups – Hydrolysis
17.10 – Reaction with Primary Amines – Imines
17.10 – Reaction with Primary Amines – Imines
opsin
17.10 – Reaction with Primary Amines – Imines
17.11 – Reaction with Secondary Amines – Enamines
17.12 – The Wittig Reaction
Phosphonium salt
Wittig ylide
17.12 – The Wittig Reaction
17.12 – The Wittig Reaction
Retrosynthesis:
Synthesis:
17.13 – Planning an Alkene Synthesis by the Wittig Reaction
17.14 – Stereoselective Addition to Carbonyls
17.15 – Oxidation of Aldehydes (via the Hydrate)
17.16 – Baeyer-Villager Oxidation of Ketones
17.16 – Baeyer-Villager Oxidation of Ketones