Aldehydes Claisen-Schmidt reaction

The cross-aldol addition of a ketone to an aldehyde (Claisen-Schmidt reaction) is profitably carried out by using the silyl enol ether of the ketone in an organic solvent in the presence of TiCh (Mukaiyama reaction) [2], but this protocol is not suitable for acid-sensitive substrates. High pressure may be employed in place of the catalyst, but longer reaction times are required [4]. 

Claisen-Schmidt reaction. Aromatic aldehydes condense with aliphatic or mixed alkyl-aryl ketones in the presence of aqueous alkali to form ap-unsaturated ketones ... 

The above are examples of the Claisen - Schmidt reaction. The formation of p-nitrostyrenes by reaction of nitroalkanes with aromatic aldehydes in the presence of aqueous alkali may be included under the Claisen- hmidt condensation ... 

By catalytic reduction of a p-unsaturated ketones, prepared from aldehydes by the Claisen - Schmidt reaction (see under Aromatic Aldehydes), for example ... 

Claisen-Schmidt reaction (Section 18.10) A mixed aldol condensation in which an aromatic aldehyde reacts with an enolizable aldehyde or ketone. 

The Claisen-Schmidt reaction (Figure 11-17) produces an a,P-unsaturated aldehyde or ketone, the general structure of which is shown in Figure 11-18. The Claisen-Schmidt reaction is a crossed aldol condensation. 

Claisen-Schmidt Reaction The production of an a,P-unsaturated aldehyde or ketone from an aldehyde or ketone in the presence of strong base. 

Reaction between two different aldehydes. In the most general case, this will produce a mixture of four products (eight, if the olefins are counted). However, if one aldehyde does not have an a hydrogen, only two aldols are possible, and in many cases the crossed product is the main one. The crossed aldol reaction is often called the Claisen-Schmidt reaction. 

A retrosynthetic analysis of a,/J-unsaturated ketones leading to various methods of synthesis is outlined in Section 5.18.2, p. 798. These methods are equally applicable to aromatic aldehydes. Aromatic aldehydes condense with aliphatic or mixed alkyl aryl ketones in the presence of aqueous alkali to form a,[i-unsaturated ketones (the Claisen-Schmidt reaction). 

Ketones and aldehydes can also be linked by the same method, i.e. a reaction called the Claisen-Schmidt reaction. The most successful reactions are those where the aldehyde does not have an a-proton ... 

The aldol condensation of ketones with aryl aldehydes to form a,p-unsaturated derivatives is called the Claisen-Schmidt reaction ° . ... 

In the Claisen-Schmidt reaction, aliphatic aldehydes and ketones are the sources of the carbanion and the products are unsaturated aldehydes and ketones. In the reaction with acetaldehyde (ethanal), cinnamaldehyde (3-phenylpropenal) is formed. With acetone, 4-phenylbut-3-enone (benzyli-deneacetone) is the product (Scheme 6.18). The reaction is generally applicable and a large variety of products have been obtained in this way, some of which are used in perfumery. 

Reaction between Two Different Aldehydes. In the most general case, this will produce a mixture of four products (eight, if the alkenes are counted). However, if one aldehyde does not have an a hydrogen, only two aldols are possible, and in many cases the crossed product is the main one. The crossed-aldol reaction is often called the Claisen-Schmidt reaction. The crossed aldol is readily accomplished using amide bases in aprotic solvent. The first aldehyde is treated with LDA in THF at —78°C, for example, to form the enolate anion. Subsequent treatment with a second aldehyde leads to the mixed aldol product. The crossed aldol of two aldehydes has been done using potassium ferf-butoxide and Ti(OBu)4. ... 

The reaction of an aldehyde with a ketone employing sodium hydroxide as the base is an example of a mixed aldol condensation reaction, the Claisen-Schmidt reaction. Dibenzalacetone is readily prepared by condensation of acetone with two equivalents of benzaldehyde. The aldehyde carbonyl is more reactive than that of the ketone and therefore reacts rapidly with the anion of the ketone to give a /3-hydroxyketone, which easily undergoes base-catalyzed dehydration. Depending on the relative quantities of the reactants, the reaction can give either mono- or dibenzalacetone. 

Claisen-Schmidt reaction The cross condensation reaction of an aromatic aldehyde with a simple aliphatic aldehyde or ketone with 10% KOH to yield the dehydrated product, i.e. an a,P-unsaturated arenone. 

The Claisen-Schmidt Reaction. When aromatic aldehydes are treated with aliphatic ketones in the presence of base, three reactions might be expected a Cannizzaro reaction of the aromatic aldehyde an aldol-type reaction of the ketone or a crossed aldol reaction between the ketone and the aromatic aldehyde. In either of the last two possibilities dehydration might also occur. Undoubtedly all these reactions will take place in strong base, but by employing about 10 per cent aqueous sodium hydroxide, good yields are often obtained of j3-unsaturated carbonyl conipounds derived from a crossed aldol reaction between the aldehyde and the ketone. This reaction, generally called a Claisen-Schmidt reaction, can be illustrated by the synthesis of benzalacetophenone.16... 

Claisen-Schmidt reaction on a solid phase A glass vial was charged with aldehyde resin 106 (250.0 mg, 0.1 mmol) in anhydrous dimethoxyethane (5.0 mL) and LiOH H2O (48.0 mg, 2.0 mmol, 20 equiv.) and the appropriate methyl ketone (2.0 mmol, 20 equiv.) were added. The capped vial was shaken for 16 h at rt. The resin was then washed consecutively with glacial acetic add, DMA, iPrOH, and GH2GI2 and dried in vacuo. 

Similar transformations can be obtained in the reactions of acetone with aromatic aldehydes, the classic Claisen-Schmidt reaction. These reactions invariably give the a,p-unsaturated ketone products. Either the mono- or bis-condensation product may be obtained by suitable adjustment of the reaction conditions (equation 45 and 46). 46... 

Many reports have focused on the functionalization and derivatization of cyclo-pentadienyl groups bound to iron in ferrocene complexes. As an example, a series of ferrocenyl esters have been prepared via solvent-free reactions of ferrocenoyl fluoride with substituted phenols after microwave heating for just 1 min. " In the case of 4-bromophenol, the YIF was 1.2, but most substrates gave somewhat lower yields than the conventional method. However, the microwave approach did not require the addition of A, A -dimethylaminopyridine that was necessary conventionally. Other reports include a green approach to the acylation of ferrocene using the polymeric sulfonic acid Nation as an acid catalyst " and a one-pot approach to the synthesis of l,5-dioxo-3-substituted[5]ferrocenophanes from l,T-diacetylferrocene and aldehydes via a Claisen-Schmidt reaction. " " ... 

Claisen-Schmidt Condensation. The base-catalyzed condensation between an aromatic aldehyde and a ketone to yield an a ,/3-unsaturated ketone and a water molecule is known as the Claisen-Schmidt reaction (49,50). This reaction is mechanistically related to the Knoevenagel condensation, and in many aspects this reaction can be regarded as a particular case of it. 

Purpose, The synthetically useful aldol reaction is investigated as a method of forming carbon-carbon bonds. It is a general reaction of aldehydes that may also be extended to ketones. The specific case outlined in this experiment is known as the Claisen-Schmidt reaction. Experiments [A3a] and [FI] provide other examples of the aldol condensation. 

The aldol reaction (aldol condensation) is one of the fundamental reactions of organic chemistry, since it leads to the formation of a new carbon-carbon bond and is broadly applicable. A condensation reaction is one in which two molecules are joined with the concomitant expulsion of a small stable molecule, usually water or an alcohol. The aldol reaction may be used to condense various combinations of aldehydes and ketones. The mixed aldol condensation of an aldehyde having no a-hydrogen atom with a ketone is specifically known as the Claisen-Schmidt reaction. This variation of the aldol condensation is illustrated here in the synthesis of dibenzalacetone. 

Claisen head adapter, 20, 26,134 Claisen-Schmidt reaction, 309-317 classification tests, 640-654. See also qualitative analysis alcohols, 640-642 aldehydes, 642-644 alkanes, 644-645 alkenes, 645 alkyl halides, 645-646 aUcynes, 645 amides, 647-648 amines, 648-649 ammonium salts, 647-648 aromatic hydrocarbons, 649-650 carboxylic acids, 650 cycloalkanes, 644-645 defined, 630 enols, 653-654 esters, 650-651 ethers, 651... 

Claisen-Schmidt reaction of acetophenones with aromatic aldehydes in presence of cationic surfactants such as cetylammonium compounds, CTACl, CTABr, (CTA)2S04 and CTAOH in mild alkaline conditions give chalcones, which on cyclisation give flavanols (Scheme 51). 

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