Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Claisen condensations with

Figure 10.3-22. Coinparison of a Claisen condensation with its biochemical counterpart. Figure 10.3-22. Coinparison of a Claisen condensation with its biochemical counterpart.
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... [Pg.93]

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. ... [Pg.98]

Mixed Claisen-like reactions can also be carried out between an ester and a ketone, resulting in the synthesis of a jS-diketone. The reaction works best when the ester component has no a hydrogens and thus can t act as the nucleophilic donor. For example, ethyl formate gives high yields in mixed Claisen condensations with ketones. [Pg.891]

The esters LXXVIII and LXXIX also fail to undergo the Claisen condensation with sodium ethoxide as the catalyst, but do give the reaction if mesitylmagnesium bromide is used.480... [Pg.224]

The general mechanism of the Claisen condensation, with ethoxide as the base, is shown in Figure 15-2. Sodium ethoxide is necessary because the starting material is an ethyl ester. If the starting material were a methyl ester, then the base would be sodium methoxide. Choosing a base that matches the type of ester minimizes the formation of other products. [Pg.263]

In a novel procedure, chemical modification of uncrosslinked atactic polystyrene by acetylation followed by a Claisen condensation with ethyl perfluoro-propanoate has been used to prepare a macromolecular ligand bearing phenyl,... [Pg.95]

The above reactions have been illustrated for 2- and 4-alkylpyridines. They generally fail if no heteroatom is a or 7, as in 3-alkylpyridines and 5-alkylpyrimidines. a- and [3-Alkyl groups in pyridine A-oxides are somewhat more reactive than those on the corresponding pyridines. In addition to the reactions already mentioned, 2-picoline 1-oxide undergoes Claisen condensation with ethyl oxalate to yield the pyruvic ester (630) (for the conversion of alkyl substituents in A-oxides into CH,OAc groups see Section 3.2.3.12.5.iv). [Pg.258]

Methyl groups in the 2-, 4- or 6-position of pyrimidine are also more reactive. In addition to typical reactions such as condensation with benzaldehyde, selenium dioxide oxidation and halogenation, they can be converted into oximino groups by nitrous acid, and undergo Claisen condensation with (C02Et)2. In the reaction of 2,5-dimethylpyrimidine with benzaldehyde, only the electrophilic 2-methyl group reacts preferentially to yield the 2-styryl derivative (631). In quinazolines partial double bond fixation makes a methyl group in the 4-position more reactive than that in the 2-position. [Pg.258]

Amino groups in compounds of type (23, Z=NH) are frequently derived from nitro groups. In the Reissert indole synthesis, o-nitrotoluene undergoes Claisen condensation with oxalic ester to yield the pyruvic ester (24). When this is reduced with Zn-AcOH the corresponding amino derivative spontaneously cyclizes to the 2-ethoxycarbonylindole (25) (63OS(43)40). [Pg.608]

Upon treatment with a base, the activated methyl group in 2-hydroxyacetophenone is converted into a carbanion. Claisen condensation with an ester gives rise to a 1,3-diketone, the sodium salt of which may be isolated although this process is usually unnecessary. Cyclization to the chromone occurs readily in acid solution (Scheme 147). [Pg.816]

The biosynthesis of the polyketide moiety is thought to involve the condensation of coenzyme A esters of acetic acid with malonyl coenzyme A to give thiol esters of 3-keto acids. Further Claisen condensations with malonyl coenzyme A add further ketone units, leading to 3,5-diketo, 3,5,7-triketo acids and so on as their thiol esters. Intramolecular condensations subsequently afford heterocyclic or aromatic structures (Scheme 275). [Pg.874]

Ethyl oxalate51,174 undergoes a Claisen condensation with a C-5 methyl group as shown in Eq. (60). [Pg.100]

Carboxylation of CHsCOS—ACP yields a propanedioyl thioester, 6, which then undergoes a Claisen condensation with a second mole of CH3COS—ACP accompanied by decarboxylation to yield a 3-oxobutanoyl thioester, 7 ... [Pg.1481]

The reactivity of the a-methylene group in lactams allows Claisen condensation with esters of formic, oxalic, and arylcarboxylic acids. Treatment of ethyl formate with A-methylpiperidone, followed by acidification, yields a salt of 1 -methyl- J2-piperideine, whereas in an alkaline medium its dimer was isolated.34- 158 With oxalic acid ester as the condensing reagent, 1-methyl-J2-pyrroline-2-carboxylic acid159 and l-methyl-d2-piperideine-2-carboxylic acid160 were obtained (Scheme 4). [Pg.175]

Figure 13.50 outlines how esters in general (not shown) and especially lactones (shown) can be prepared for a one-step aldol condensation with an aldehyde they are exposed to a mixed ( crossed ) Claisen condensation with formic acid methyl ester (cf. Figure 13.59, first line). Like all Claisen condensations (Section 13.5.1), this also first leads to the formation of the enolate of the acylated ester. Unlike other Claisen condensations, this enolate is isolated. [Pg.569]

Claisen condensation of acetoacetate dianion.3 In the presence of BF3 etherate the dianion of acetoacetate undergoes Claisen condensation with the tetra-methyldiamides of dicarboxylic acids 1 to form polyketides (2, equation I). The... [Pg.46]

Chromium trioxide, 21, 6 24, 39, 76 Cinnamic acid, 20, 77 22, 26 24, 21 Cinnamoyl chloride, 20, 77 24, 21 Citral, bisulfite compound, 23, 78 purification of, 23, 78 Claisen condensation, with acetone and ethyl formate, 27, 92 with ethyl oxalate and ethyl succinate, 26,42... [Pg.102]

The monobromide(s) 146 were treated under strong basic conditions at elevated temperature, slowly generating the y-lactone 147 by ring opening, and consecutive Sn2 reaction in 87% yield (Scheme 14). The isopropyl group was introduced in a four-step sequence. Claisen condensation with methyl formate led to a mixture of the enol and the enol ether, which by treatment with diazomethane, yielded in 80% the enol ether, 148. To introduce the methyl groups, the enol ether was converted into the thioenol ether. 1,4-Addition of dimethyl copper lithium afforded the... [Pg.140]

Reduction of the carbethoxy group to the hydroxymethyl group with lithium aluminum hydride at — 35° and Claisen condensation with ethyl acetate are known to take place with pyridazinecar-boxylic acids. 6-Oxo-l,6-dihydro-2-pyridazinyl aliphatic acids, having the pyridazinonyl residue attached at the a-position of the aliphatic radical, readily undergo decarboxylative acylation with acid anhydrides in the presence of pyridine to form the corresponding 2-alkanones (107). [Pg.280]

Methyl ethyl ketone can be made to undergo the Claisen condensation with a given ester to yield either of two products, depending upon experimental conditions, (a) What are these two products (b) How could you tell quickly and simply which product you had obtained Note Use ethyl benzoate as the ester.)... [Pg.724]


See other pages where Claisen condensations with is mentioned: [Pg.88]    [Pg.236]    [Pg.117]    [Pg.152]    [Pg.51]    [Pg.441]    [Pg.950]    [Pg.579]    [Pg.51]    [Pg.99]    [Pg.950]    [Pg.29]    [Pg.177]    [Pg.88]    [Pg.88]    [Pg.724]   
See also in sourсe #XX -- [ Pg.832 ]




SEARCH



Claisen condensation

Claisen condensation acylation, ketones with esters

Claisen condensation ketone enolate reaction with esters

Claisen condensation with amides

Claisen condensation with ketones

Claisen condensation with malononitrile

Claisen condensation, with acetone and

Claisen condensation, with acetone and ethyl formate

Claisen-Schmidt condensations with substituted benzaldehydes

Ethyl acetate: Claisen ester condensation with

Ketones Claisen condensation with esters

© 2024 chempedia.info