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LDA and Kinetic Enolates

LDA and Kinetic Enolates - UCLA Chemistry 30C LDA and...

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UCLA Chemistry 30C LDA and Kinetic Enolate Chemistry Deprotonation of aldehydes, ketones, esters, and amides with hydroxide or alkoxide bases can lead to problems with the regiochemistry of reaction or with over-reaction. That is because these thermodynamic bases only generate small concentrations of the enolate and the reaction product must then be exposed to base also. O O + NaOH + H 2 o Na pKa = 20 pKa = 16 Strong bases, with a conjugate acid much less acidic than the substrates being deprotonated, deprotonate substrates without any reversibility. Such reactivity provides control over reaction regioselectivity and can limit overreaction. Enolates are formed quantitatively and then react with electrophiles completely. LDA, lithium diisopropylamide, is a common strong base that is also sterically hindered to prevent nucleophilic reactions. In the example below, the pKa difference of 17 will guarantee that the reaction is not reversible. Reactions are performed in aprotic polar solvents such as THF.
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