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Carbonyl groups condensation reactions

Olefins conjugated with electron-withdrawing groups other than a carbonyl group undergo reactions with enamines in a manner similar to the carbonyl-conjugated electrophilic alkenes described above. Namely, they condense with an enamine to form a zwitterion intermediate from which either 1,2 cycloaddition to form a cyclobutane ring or simple alkylation can take place. [Pg.222]

The classical method for preparing isoxazole involves the condensation of 1,3-dicarbonyl compounds with hydroxylamine, a reagent that contains the preformed N—O bond. The regiochemistry of the reactions can usually be rationalized by assuming that the first step involves imine bond formation at the more reactive carbonyl group. Thus, reaction of formyl ketone (44-1) with hydroxylamine gives... [Pg.266]

Dioxopentane, its 1,5-di- -alkyl-substituted derivatives, and its derivatives with one or two alkyl groups on the carbon atom joining the two carbonyl groups, condense with tellurium tetrachloride in refluxing chloroform to produce 3,5-dioxotellurane 1,1-dichlorides. The reaction does not proceed with l,l-dialkyl-2,4-dioxopentanes, 1,1,5,5-tetraalkyl-2,4-dioxopentanes, or with 1,5-diisopropyl-2,4-dioxopentane. [Pg.535]

Introduction. The reactions of aldehydes and ketones can be conveniently divided into three groups (1) reactions involving an addition to the carbonyl group, (2) reactions involving oxidation-reduction of the carbonyl group, and (3) condensation and polymerization reactions. [Pg.191]

The first stage in fatty acid biosynthesis is a condensation between acetyl CoA (the starter unit) and malonyl CoA with the loss of CO2. This reaction could be drawn like this, with CO2 being lost as the new C—C bond is formed. When chemists use malonates, we like to make the stable enol using both carbonyl groups, condense, and only afterwards release CO2 (Chapter 25). As you saw on p. 1158, nature does this in making acetoacetyl CoA during alkaloid biosynthesis, but here things work differently. [Pg.1162]

The addition reaction of enolates with carbonyl compounds is of very broad scope and is of great synthetic importance. Essentially all of the enolates introduced in Chapter 7 are capable of adding to carbonyl groups. The reaction is known as the generalized aldol condensation. [Pg.458]

Most of the characteristic reactions of ketones (RR CO) depend upon condensation with substituted amines. The reactions occur between the carbonyl group and the —NHj group of the substituted amine, and hence are also shared by aldehydes RHCO ... [Pg.341]

In this section we turn to a consideration of the experimental side of condensation kinetics. The kind of ab links which have been most extensively studied are ester and amide groups, although numerous additional systems could also be cited. In many of these the carbonyl group is present and is believed to play an important role in stabilizing the actual chemical transition state involved in the reactions. The situation can be represented by the following schematic reaction ... [Pg.282]

MEK is a colorless, stable, flammable Hquid possessing the characteristic acetone-type odor of low molecular weight aUphatic ketones. MEK undergoes typical reactions of carbonyl groups with activated hydrogen atoms on adjacent carbon atoms, and condenses with a variety of reagents. Condensation of MEK with formaldehyde produces methylisopropenyl ketone (3-methyl-3-buten-2-one) ... [Pg.488]

Many variants of this procedure exist. Thus, Kano and coworkers have carried out the condensation of /3-keto sulfoxides with diaminomaleonitrile (Scheme 36) (78S372). This reaction probably yields an intermediate dihydropyrazine which is oxidized under the reaction conditions, and it seems likely that the condensation of the carbonyl group and the amine is the first step. [Pg.180]

Monooximes of a-diketones have found applicability in the synthesis of 2-aminopyrazine 1-oxides by condensation with a-aminonitriles, and this reaction was used by White and coworkers in an approach to the synthesis of Cypridina etioluciferamine (Scheme 66 R = 3-indoloyl) (73T3761). In this instance, the use of TiCU as a catalyst was essential, since the carbonyl group in 3-acylindoles is normally deactivated and the required amine/carbonyl condensation is impractically slow. Under normal circumstances the carbonyl group in simple alkyl-substituted monoximes of a-diketones is the more reactive site and the reaction is rapid, requiring no catalysis (69LA(726)loo). [Pg.187]

Scheme 4 shows in a general manner cyclocondensations considered to involve reaction mechanisms in which nucleophilic heteroatoms condense with electrophilic carbonyl groups in a 1,3-relationship to each other. The standard method of preparation of pyrazoles involves such condensations (see Chapter 4.04). With hydrazine itself the question of regiospecificity in the condensation does not occur. However, with a monosubstituted hydrazine such as methylhydrazine and 4,4-dimethoxybutan-2-one (105) two products were obtained the 1,3-dimethylpyrazole (106) and the 1,5-dimethylpyrazole (107). Although Scheme 4 represents this type of reaction as a relatively straightforward process, it is considerably more complex and an appreciable effort has been expended on its study (77BSF1163). Details of these reactions and the possible variations of the procedure may be found in Chapter 4.04. [Pg.121]

The addition of the a-carbon of an enolizable aldehyde or ketone 1 to the carbonyl group of a second aldehyde or ketone 2 is called the aldol reaction It is a versatile method for the formation of carbon-carbon bonds, and is frequently used in organic chemistry. The initial reaction product is a /3-hydroxy aldehyde (aldol) or /3-hydroxy ketone (ketol) 3. A subsequent dehydration step can follow, to yield an o ,/3-unsaturated carbonyl compound 4. In that case the entire process is also called aldol condensation. [Pg.4]


See other pages where Carbonyl groups condensation reactions is mentioned: [Pg.481]    [Pg.970]    [Pg.206]    [Pg.481]    [Pg.829]    [Pg.75]    [Pg.234]    [Pg.829]    [Pg.1210]    [Pg.170]    [Pg.189]    [Pg.77]    [Pg.982]    [Pg.826]    [Pg.4]    [Pg.729]    [Pg.79]    [Pg.248]    [Pg.293]    [Pg.50]    [Pg.94]    [Pg.470]    [Pg.399]    [Pg.117]    [Pg.180]    [Pg.312]    [Pg.1057]    [Pg.569]    [Pg.620]    [Pg.812]    [Pg.289]    [Pg.121]    [Pg.178]    [Pg.145]    [Pg.234]   
See also in sourсe #XX -- [ Pg.454 , Pg.458 ]




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