Preparation by Claisen condensation

The 1,3-dicarbonyl components can be replaced by an enol ether, which can be prepared by Claisen condensation from an ortho ester and a reactive methylene compound. ... 

An important group of acylation reactions involves esters, in which case the leaving group is alkoxy or aryloxy. The self-condensation of esters is known as the Claisen condensation.216 Ethyl acetoacetate, for example, is prepared by Claisen condensation of ethyl acetate. All of the steps in the mechanism are reversible, and a full equivalent of base is needed to bring the reaction to completion. Ethyl acetoacetate is more acidic than any of the other species present and is converted to its conjugate base in the final step. The (3-ketoester product is obtained after neutralization. 

An important group of these reactions involves esters, in which case the leaving group is alkoxy or aryloxy. The self-condensation of esters is known as the Claisen condensation. 118 Ethyl acetoacetate, for example, is prepared by Claisen condensation of ethyl... 

The method described is that of Hampton, Harris, and Hauser6 and is an improvement over the benzyne method, which gives poor yields.6,7 This /J-diketone has been prepared by Claisen condensation of ethyl phenylacetate with acetone,8 but the yield is poorer and the product has been shown by gas chromatography to be impure.6 The j8-diketone has also been prepared by the hydrolysis of 4-methoxy-5-phenyl-3-penten-2-one and by hydrolysis and decarboxylation of ethyl a-acetyl-/3-oxo-y-phenylbutyrate10 but these compounds are more difficult to obtain than the starting materials used in the present synthesis. 

Methyl cinnamate is a colorless crystalline solid mp 36.5 °C) with a fruity, sweet-balsamic odor. In addition to the common esterification methods, it can be prepared by Claisen condensation of benzaldehyde and methyl acetate in the presence of sodium. Methyl cinnamate is used in soap perfumes, as well as in blossom and oriental perfumes, and is sometimes added to aromas. 

The statine 12 was prepared by Claisen condensation of valine with methyl acetate followed by stereoselective reduction of the /J-keto ester, following precedents as in Jouillie s total synthesis [38] of tamandarin. The Boc group... 

The following ketones cannot be synthesized by the acetoacetic ester method (why ), but they can be prepared by a modified version of it. The modification includes the preparation (by Claisen condensation) and use of an appropriate 3-ketoester, O O... 

The thenyl cyanides are of great importance for the preparation of thiophene derivatives. Because of the acidifying effects of both the thienyl and of the cyano groups, carbanions are easily obtained through the reaction with sodamide or sodium ethoxide, which can be alkylated with halides, carbethoxylated with ethyl carbonate, or acylated by Claisen condensation with ethyl... 

Acetoacetic Ester can be prepared by the condensation of ethyl acetate, called the Acetoacetic Ester Condensation Reaction, a Claisen Condensation-. 

Figure 6.6 Trapezoidal macrocycles prepared by Claisen-Schmidt condensation of one flexible female-female connector with a flexible male-male connector. (Macrocycle 27 crystallizes as a hydrate with a hydrogen-bonded bridging water molecule between the phenolic moieties.)...

Chalcones (123) are commonly prepared by Claisen-Schmidt or aldol condensation. An important way to synthesize chalcones (123) is the Friedel-Crafts acylation involving treatment of acid chlorides (121) with arenes (122). Such a protocol for the synthesis of chalcones (123) was developed by More et al. (2012) using nano-ZnO heterogeneous catalyst under solvent-free conditions at room temperature (Scheme 9.38). Arenes (122) of all sorts, activated as well as unactivated, reacted smoothly to afford the chalcones (123) in excellent yield. High regioselectivity was observed during the course of reaction, which occurred selectively at the para-position of OMe, Br, Me, and Cl. 

A series of racemic 6-acyl-2-methoxy-5,6-dihydro-(2H)-pyrans (295) has been prepared from the corresponding 6-alkoxycarbonyl derivatives by Claisen condensation with alkyl esters and subsequent decarboxylation of the resulting jS-keto-esters. ... 

Cl - Preparation by Claisen-Schmidt condensation of p-chlorobenzaldehyde with 2-hy droxy- 5 -propionyl-acetophenone in COCH2CH3 the presence of potassium hydroxide in... 

This preparation was discovered independently by Geuther (1863) and by Frankland and Duppa (1865). The reaction was subsequently investigated in detail and so w idely extended by Claisen that it has become solely a specific example of the more general process known as the Claisen Condensation. Claisen showed that an ester under the influence of sodium ethoxide would not only condense with itself (as in the preparation of ethyl acetoacetate), but also with (i) another ester, (ii) a ketone, if of formula RCHgCOR, (iii) a nitrile, if of formula RCH CN, in each case with the elimination of alcohol. Examples of these modifications are ... 

The preparation of benzoylacctone Is another example of the acylation of a ketone (acetophenone) by ethyl acetate to a p diketone (Claisen condensation compare preceding Section) ... 

Ethyl acetopyruvate has been prepared only by the condensation of ethyl oxalate and acetone in the presence of sodium ethylated The method given above is based on that of Claisen and Stylosd... 

Ethyl ethoxalylpropionate has been prepared by the Claisen condensation of ethyl oxalate with ethyl propionate as above, and by the alkylation of ethyl ethoxalylacetate. ... 

Ethyl acetoacetate (acetoacetic ester), available by the Claisen condensation of ethyl acetate, has properties that make it a useful starting material for the preparation of ketones. These properties are... 

Preparation of Heterocyclic Enamines by Means of Claisen Condensation of Lactams... 

The carbanions derived from acylthiophenes have been condensed with aldehydes,and, through the Claisen condensation with esters, thienylsubstituted -diketones have been obtained. 2-Thenoyl trifluoroacetone, first prepared by Reid and Calvin through the Claisen condensation of 2-acetylthiophene with ethyl trifluoracetate, has become an extremely useful chelating agent for the extraction of numerous elements from strongly acidic solutions, The tautomeric form which dominates in aqueous solution is the ketone hy-drate. Other thiophenes have also proved useful for analytical purposes. ... 

Acetylisothiazoles have been prepared by ketonic hydrolysis of the jS-ketoesters derived from the Claisen condensation on 5-ethoxycar-bonylisothiazoles. 5-Acetyl-3-methylisothiazole is also obtained from the reaction of 5-cyano-3-methylisothiazole with methylmagnesium iodide. ... 

It Is of Interest to note that the preparation of dimethyldihydroresorcinol (also named dimed one and methone Section VII, 15) involves an initial IVIichael addition to mesityl oxide, followed by an internal Claisen condensation. 

Synthesis of pyrazole 3 by the Medicinal Chemistry route was straightforward from N-Boc isonipecotic acid (45), so we utilized the route after some optimizations, as summarized in Table 2.4. The key 1,3-diketone intermediate 48 was prepared from 45 without issues. A minor problem in the original route was the exothermic nature of the Claisen condensation between methyl ketone 47 and methyl phenylacetate. Slow addition of l.lequiv of methyl phenylacetate to a mixture of 47, 0.2equiv of MeOH, and 2.5equiv of NaH in THF at room temperature solved this exothermic issue and reduced the amount of self-condensation of... 

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