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Mixed Aldol Reaction and Condensations

The net loss of H and OH represents the loss of water, therefore the term aldol condensation.

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Dibenzalacetone does not undergo the aldol condensation ..

The reaction of carbonyl compound enolates with aldehydes and ketones to form a β-hydroxy carbonyl compound is the Aldol Reaction, if conditions result in a subsequent dehydration to form the α,β-unsaturated compound, then the reaction is termed the Aldol Condensation (loss of a molecule of water). These reactions represent a very large and complex area of chemistry. Chemists have developed techniques to successfully convert almost all possible combinations of donors (the enolate) and acceptors (the aldehyde or ketone) to aldol products. Crossed aldol reactions in which the acceptor is an aromatic aldehyde are sometimes called Claisen-Schmidt Condensations.

are formed in the aldol condensation of dibenzalacetone?
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Mukaiyama aldol reactions are Lewis acid catalyzed (the acceptor is an oxy-substituted carbonium ion, the donor an enol silyl ether). Psymberin: Rech, J. C.; Floreancig, P. E. 2005, , 5175-5178.

The Aldol Reaction and Condensation

This mechanism is known as an Aldol Condensation Reaction, a base-catalyzed dimerization of two aldehydes with a a hydrogen atom.
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In this synthesis of Ferruginol, a second Robinson annulation was performed on the enone product. Note that under these equilibrating conditions it is the conjugated enolate (not the cross-conjugated one) that reacts.

Robinson annulations can also be initiated by the reaction of preformed enolates with Michael acceptors. However, reactions with methyl vinyl ketone are often unsuccessful, because the enolate which is formed in the conjugate addition is very similar in reactivity to the starting enolate. The α-trimethylsilylvinyl methyl ketone introduced by Stork (sometimes called the Stork-Ganem Reagent - . 1973, , 6152.) solves this problem - the trimethylsilyl-substituted enolate product is more hindered, and the anion somewhat stabilized by silicon, so a second conjugate additions (polymerization) is inhibited. In the example below the enolate is formed by conjugate addition of an organocuprate. The silyl group is readily removed during the hydroxide catalyzed aldol reaction. Hispidospermidine: Frontier, A. J.; Raghavan, S.; Danishevsky, S. J. . 2000, , 6151.

Aldol Condensation - Synthesis of Dibenzalacetone

On the other hand, if we add a catalytic amount of weak base, rather than a full equivalent, a small amount of enolate ion will be generated.
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The Robinson Annulation involves a Michael addition of an enolate (typically of a 1,3-dicarbonyl compound) to form a 1,5-dicarbonyl compound. These conjugate additions are successful because the 1,2-addition of the enolates to the enone is highly reversible, and usually has an unfavorable equilibrium. In some cases this step is performed separately, but often continued treatment by base leads to an intramolecular aldol condensation to form the final product, a cyclohexenone, as in the example below: Synthesis of Ferruginol: Snitman, D. L.; Himmelsbach, R. J.; Watt, D. S. , 1978, , 4758.

A much more general approach to controlling aldol reactions is to use preformed enolates or enol derivatives. Lithium enolates of ketones, esters, lactones and amides usually react cleanly with aldehyde substrates. Ester, amide and carboxylate enolates also react well with ketones to form aldol products, but intermolecular ketone-ketone crossed aldols are generally unsuccessful with alkali metal enolates, as are most aldol reactions involving aldehyde enolate donors.

The only experiment performed with the assistance of this lab manual was on page 101-103, Semi-Microscale Aldol Condensation.
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Pdf files for Aldol reaction synthesis of ..

The X-ray structure of a Reformatsky reagent has been reported (Dekker, J. 1983, 553). Both carbon and oxygen are bonded to zinc. Ketone zinc enolates seem to be O-zincated (Hansen, M. M.; Bartlett, P. A.; Heathcock, C. H. ., 1987, , 2069)


The Reformatsky reaction involves the reduction of an α-halo carbonyl compound (usually a bromo ester) with zinc to form a zinc enolate, which condenses with an adehyde or ketone. Classically the reaction was performed under Barbier conditions (ketone, halide and zinc mixed), but separate preparation of the reagent has some significant advantages.

Aldol Condensation - Organic Chemistry Portal

If a full equivalent of strong base is added and the carbonyl compound is rapidly and completely converted into its enolate ion at a low temperature, with the addition of an electrophile to quench the reactive enolate ion, no condensation can take place.

Aldol Condensation Synthesis of Dibenzalacetone ..

Metaloenamines (azaenolates) can be used for those crossed Aldol Reactions (ketone-donor/ketone-acceptor and aldehyde-donor) that cannot be done using preformed lithium enolates.

Synthesis of Dibenzalacetone by Aldol Condensation

Since the newly formed ketone still possessed alpha hydrogens, it too underwent the same enolate condensation reaction with a second mole of benzaldehyde to form the final product, dibenzalacetone.

The Aldol Condensation: Synthesis of Dibenzalacetone

Aldol reaction with ester enolate: synthesis of Ginkolide B: Corey, E. J.; Kang, M. C.; Desai, M. C.; Ghosh, A. K.; Houpis, I. N. 1988, , 649-651.

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