Enolates and Carbanions 2 (1)
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Transcript of Enolates and Carbanions 2 (1)
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75
Sample problem: (sd-61)
How would you prepare the following compound by an enamine
synthesis?
Alkylation of the -carbon: (sd-62)
THE MICHAEL REACTION
Addition of enolate ion to the -carbon of , -unsaturated carbonyl
compound Michael Reaction.
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Stork Enamine Reaction (Sd-64)
When an enamine is used as a nucleophile in place of an enolate in
a Michael reaction, the reaction is called Stork Enamine Reaction.
ALDOL CONDENSATION: (sd-65)
A reaction between two molecules of RCHO/RCOR with -
hydrogen in basic condition -hydroxy aldehyde or -hydroxy
ketone.
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Dehydration of Aldol addition product (sd-66)
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Dehydration sometimes occurs under the conditions in which the
aldol addition is carried out (without additional heating)(sd-67).
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Crossed Aldol Condensations: (sd-68)
Condensation between two carbonyl compounds (only one of the
carbonyl compounds has -hydrogen)
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Intramolecular Aldol reactions: Certain dicarbonyl compounds
when treated with base undergo intramolecular aldol
reactionscyclic products (5/6-membered).
MECHANISM:
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Synthesis using aldol condensations (sd-70)
Aldol condensation 1. -hydroxy aldehyde or ketone
2. --unsaturated aldehyde/ketone
Therefore look for these two functional groups and decide which
aldehydes/ketones must be used for the starting materials.
Knoevenagel condensation (sd-71)
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The Claisen condensation: (73)
Condensation involving molecules of an ester (with -H) in the
presence of base a -keto ester.
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Crossed Claisen condensation: ( sd-74)
Condensation between two different esters; Best results (to avoid
mixtures) are obtained if only one of the esters has -H)
Condensation between ketones and esters (either contain -H or
not)
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Both having H- :(sd-74a)
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The Robinson Annulation (sd-79)
A ring forming reaction that involves:
i) A Michael Reaction- to form a 1,5-diketone
ii) 1,5-diketone undergoes an intramolecular aldol addition
cyclic compound
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