Condensation carbonyl compounds

I. Condensation of N-Monosubstituted Hydroxylamines with Carbonyl Compounds Condensation of N -monosubstituted hydroxylamines with carbonyl compounds is used as a direct synthesis of many acyclic nitrones. The synthesis of hydroxylamines is being carried out in situ via reduction of nitro compounds with zinc powder in the presence of weak acids (NH4CI or AcOH) (14, 18, 132). The reaction kinetics of benzaldehyde with phenylhydroxylamine and the subsequent reaction sequence are shown in Scheme 2.21 (133). 

Certain Carbonyl Compounds. Condensations and Reductions. J. Amer. chem. Soc. 68, 2647 (1946). 

Condensations are some of the most important enolate reactions of carbonyl compounds. Condensations combine two or more molecules, often with the loss of a small molecule such as water or an alcohol. Under basic conditions, the aldol condensation involves the nucleophilic addition of an enolate ion to another carbonyl group. The product, a /3-hydroxy ketone or aldehyde, is called an aldol because it contains both an aldehyde group and the hydroxy group of an alcoho/. The aldol product may dehydrate to an a,/3-unsaturated carbonyl compound. 

Aromatic and aliphatic carbonyl compounds condense with glycols, such as ethylene, propylene, and trimethylene glycols, to form cyclic acetals p-toluenesulfonic acid has proved to be an excellent catalyst. As before, the water formed in these reactions is conveniently removed by an azeotropic distillation with benzene. Representative aldehydes and ketones that undergo this acetalization include acetone, cyclohexanone, pinacolone, acetophenone, benzophenone, n-heptaldehyde. 

Aminoimidazoles exist as the amino tautomers. Carbonyl compounds condense normally with C-aminoimidazoles, - which can also be diazotized although some amines are rather unstable. The diazonium fluoroborates have been transformed into fluoroimid-... 

Diels-Alder reactions. Activated carbonyl compounds condense with dienes to furnish dihydropyrans at room temperature when catalyzed by BiCl,. Conventional Diels-Alder reactions catalyzed by BiClj or Bi(OTf), have also been scrutinized. ... 

If the reduction is carried out in the presence of an alkyl halide or a carbonyl compound, condensation at the a-position takes place as well as reduction. 

P-Amino carbonyl compounds. Condensation of aldehydes, amines, and ketene silyl acetals is promoted by HBF4 in an aqueous media (aq t-PrOH or in the presence of... 

Carbonyl compounds condense with amines and related functional groups (e.g., hydrazines), with elimination of water, to yield C=N double-bonded products ... 

Pyridine-2-aldehyde, 119 Pyridine alkaloids, 055 Pyridine carbonyl compounds, condensation with active methylene compounds, 341-343, 406-416... 

In acid, a second reaction, the dehydration of the p-hydroxy carbonyl compound to the a,P unsaturated aldehyde or ketone is very common, and it is generally the dehydrated products that are isolated (Fig. 19.69). In the overall reaction, two carbonyl compounds condense to produce a larger carbonyl compound and give off a small molecule— water in this case. Thus, the aldol reaction is often called the aldol condensation. 

General Discussion. (Z)-(Trimethylsilyloxy)vinyllithium (1) has essentially been used for a one-pot vinylogation of carbonyl compounds. Condensation of (1) with aldehydes and ketones (2) occurs readily at low temperature (—70 °C) then treatment of the reaction mixture with an acidic solution in mild conditions (IN hydrochloric acid, 0 °C to rt) produces the Q ,/3-unsaturated aldehydes (3), without double bond migration. The ( 0 isomers are obtained alone (from aldehydic compounds) or very predominantly (fromketonic compounds). The intermediate adducts, y-hydroxy enol ethers (4), can be isolated by slightly basic mild hydrolysis (eq l).l... 

Carbonyl compounds condense with arylhydrazines with the formation of crystalline arylhydrazones, mostly not very soluble. The reaction is used both for the detection and the identification of carbonyl compounds. 

Difunctional compounds are generally made by carbonyl compound condensation reactions. 

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