Aldol_III_LDA - The Aldol Reaction: Crossed/Directed Aldol...

Info iconThis preview shows pages 1–4. Sign up to view the full content.

View Full Document Right Arrow Icon
The Aldol Reaction: Crossed/Directed Aldol Reactions LDA is highly basic and will irreversibly deprotonate carbonyl compounds. By exposing an aldehyde or ketone to LDA at –78C, we can “pre-form” an enolate and conduct crossed aldol reactions as shown below. Note that by using a preformed enolates we may conduct aldol reactions in which both reacting partners have α -hydrogens. H 3 CC H 3 O H O R LDA, -78C 1 K e t o n e H 3 C O 1 = N u , 2 = E + OH R H 3 C O 2 H 3 H 3 O 1 p K a = 2 0 N Li L D A ( L i t h i u m D i i s o p r o p y l a m i d e ) H 3 H 2 O 1 E n o l a t e N H D i i s o p r o p y l a m i n e p K a = 3 8 K eq = 10 18 Li
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
The Aldol Reaction: Crossed/Directed Aldol Reactions Deprotonation of unsymmetrical ketones with LDA LDA is very bulky and will prefer to deprotonate the sterically less hindered α - hydrogen. However, the less substituted enolate is the less stable enolate. When the temperature is raised, the two enolates will equilibrate and the more substituted enolate, which is more stable, will predominate.
Background image of page 2
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Background image of page 4
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 4

Aldol_III_LDA - The Aldol Reaction: Crossed/Directed Aldol...

This preview shows document pages 1 - 4. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online