醛酮的Alfa位反应

1、Aldehyde & Ketone,Nucleophilic Addition to the Carbonyl Group,Oxygen Nucleophiles Sulfur Nucleophiles Carbon Nucleophiles Nitrogen Nucleophiles,Reactions at the -Carbon of Aldehyde & Ketone,Reactions at the -Carbon of Carbonyl Compounds,Acidity of the -hydrogens Keto-Enol tautomerization Application

2、s,Acidity of the -hydrogens,Keto-Enol Tautomerization,Keto,Enol,Which makes a greater contribution to the hybrid?,A. Interconversion：,B. Keto-enol tautomers in equilibrium,K,enol,keto,Monocarbonyl compounds,(99%) (1.510-4%),(100%) (extremely small),(98.8%) (1.2%),-dicarbonyl compounds,24%,76%,Phenol

3、,K 1014,C. Detection:,+ FeCl3,Purple or blue,D. Formation of enolate:,Which “Base”?,enolate,E. Regioselective Formation of Enolate Anions,?,?,Kinetic enolate,Thermodynamic enolate,Generally: 1. Low temperature gives the kinetic enolate. 2. High temperature, relatively weak base in a protic solvent g

4、ives the thermodynamic enolate.,LDA,Two special examples: 1. The kinetically favored enolate can be formed cleanly through the use of diisopropylamide (LDA). 2. In acid condition, the thermodynamic enol is formed predominantly.,enol,enolate,F. Racemization:,Application,Nucleophilic center,Nucleophil

5、ic center,Ambident nucleophile,carbanion,alkoxide anions,React as an alkoxide anions,trapped,React as a carbanion,React as a carbanion 1: Halogenation,Haloform reaction,iodoform reaction,React as a carbanion 2: Alkylation,side reaction:,solution:,React as a carbanion 3: Aldol Reaction,Reversible,easy,difficult,Soxhlet Extractor,catalyst,acetone,How does it work?,Crossed A