Aldol Condensation plays a vital role in organic synthesis, creating a path to form carbon-carbon bonds. The aldol itself is then formed, and it may then undergo dehydration to give the unsaturated carbonyl compound. Another approach is to use LDA on one ketone to form the enolate quantitatively, then to react that enolate with the other carbonyl compound. The Claisen‐Schmidt condensation is most often taken to be the condensation of an aromatic aldehyde or ketone usually in the presence of a basic catalyst. https://chem.libretexts.org/Textbook_Maps/Organic_Chemistry/Supplemental_Modules_(Organic_Chemistry)/Reactions/Organic_Reactions/Aldol_Condensation, CC BY-NC-SA: Attribution-NonCommercial-ShareAlike, https://chem.libretexts.org/Textbook_Maps/Organic_Chemistry/Supplemental_Modules_(Organic_Chemistry)/Reactions/Reactivity_of_Alpha_Hydrogens/Synthesis_of_Enols_and_Enolates, https://chem.libretexts.org/Textbook_Maps/Organic_Chemistry/Supplemental_Modules_(Organic_Chemistry)/Reactions/Reactivity_of_Alpha_Hydrogens/Aldol_Reaction, https://chem.libretexts.org/Textbook_Maps/Organic_Chemistry/Map%3A_Organic_Chemistry_(McMurry)/Chapter_23%3A_Carbonyl_Condensation_Reactions/23.05_Mixed_Aldol_Reactions, https://chem.libretexts.org/Textbook_Maps/Organic_Chemistry/Map%3A_Organic_Chemistry_(McMurry)/Chapter_23%3A_Carbonyl_Condensation_Reactions/23.04_Using_Aldol_Reactions_in_Synthesis, https://chem.libretexts.org/Textbook_Maps/Organic_Chemistry/Book%3A_Organic_Chemistry_with_a_Biological_Emphasis_(Soderberg)/13%3A_Reactions_with_stabilized_carbanion_intermediates_I/13.3%3A_Aldol_reactions. Intramolecular aldol condensation. Reactions in which two molecules of an aldehyde combine to form Î±, Î²â unsaturated aldehyde and a molecule of water are called aldol condensations. Quantitative yields in Claisen-Schmidt reactions have been reported in the absence of solvent using sodium hydroxide as the base and plus benzaldehydes. This reaction is most commonly known as aldol condensation. An example is the synthesis of dibenzylideneacetone. When aldehydes and ketones having at least one α-hydrogen are treated with dilute alkali (which act as a catalyst) they form β-hydroxy aldehydes (aldol) or β-hydroxy ketones (ketol) respectively. Hydroxide functions as a base and therefore moves the acidic a-hydrogen producing the reactive enolate ion. This is where the “head” of the molecule “bites its own tail”. The name aldol condensation is also commonly used, especially in biochemistry, to refer to just the first (addition) stage of the process—the aldol reaction itself—as catalyzed by aldolases. The general reaction of aldol condensation is. The product is the alkoxide salt of the aldol product. Mixed aldols in which both reactants can serve as donors and acceptors generally give complex mixtures of both dimeric (homo) aldols and crossed aldols. Base-catalyzed aldol reaction (shown using −OCH3 as base). This reaction is named after two of its pioneering investigators Rainer Ludwig Claisen and J. G. Schmidt, who independently published on this topic in 1880 and 1881. Dieckmann condensation contains 2 ester groups present in the same molecule, which produces cyclic molecule. Under these conditions, once the aldol addition product is formed, it rapidly loses water to form Î±, Î²-unsaturated aldehyde. In a case of Perkin reaction, enolate generated by anhydride is aromatic. Enolates are very useful in synthesis, as they represent a stabilized nucleophilic form of carbon. In this case, enolate formation is irreversible, and the aldol product is not formed until the alkoxide of the aldol product is protonated in a separate acid-base workup step. An acidic or basic solution can catalyze the condensation of aldol. In such a case, the following abbreviated formulas illustrate the possible products, red letters representing the component of the acceptor and the donor blue.If all reactions occurred at the same rate, the same quantity would be obtained for the four products. Aldol reactions are excellent methods for the synthesis of many enones or beta hydroxy carbonyls. Second, aldehydes lacking alpha-hydrogens can only function as acceptor reactants, and this reduces the number of possible products by half. is a condensation reaction in organic chemistry in which an enol or an enolate ion reacts with a carbonyl compound to form a β-hydroxyaldehyde or β-hydroxyketone, followed by dehydration to give a conjugated enone. The success of these mixed aldol reactions is due to two factors. Keto-enol tautomerization (by Jay) Retro-aldol and retrosynthesis. Because of this most mixed aldol reactions are usually not performed unless one reactant has no alpha hydrogens. Crossed aldol condensation is a variation of aldol condensation in which two dissimilar carbonyl compounds (each containing alpha hydrogens) undergo the condensation reaction together.
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