Condensations acetals

The acylation of ketones with esters an example of the Clalsen condensation is generally effected with a basic reagent, such as sodium ethoxide, sodium, sodamide or sodium hy dride. Thus acetone and ethyl acetate condense in the presence of sodium ethoxide to yield acetylacetone ... 

P-LactamsSilyl ketene acetals condense with imines in the presence of this catalyst to afford only or mainly anh -p-amino esters, which can be cyclized to trans-3-lactams. 

Stomach contents, blood, nrine Extract sample with ethyl acetate condense inject toGC GC/FID/MS 0.2 g/mL 93-100 Hara et al. 1988... 

The enolate anion attacks the carbonyl carbon of a second molecule of ester and gives a P-ketoester. Thus, the Claisen condensation is a nucleophilic acyl substitution reaction. Eor example, two molecules of ethyl acetate condense together to form the enolate of ethyl acetoacetate, which upon addition of an acid produces ethyl acetoacetate (P-ketoester). 

Stabilizing rings may also be created by forming O-isopropylidene acetals. Condensation of methyl D-ribopyranoside with acetone was shown by Levene and Stiller166 to give equal amounts of the 2,3-O-isopropylidene furanoside and the 3,4-O-isopropylidene pyranoside Barker and Spoors,157 investigating this reaction further, concluded that the isomerization occurs after the condensation with acetone. 

A Hylic sulfones (cf., 9, 132). In the presence of this Pd(0) complex, allylic acetates condense with sodium p-tolylsulfinate to form allylic sulfones (predominately E). The more substituted isomer is formed initially, but rearranges after extended reaction time to the more stable allylic sulfone.22... 

Acetate, condensation of, 236 Acetic acid, (ethylenedinitrilo)tetra-, 256... 

From Ethyl Acetate.—The simplest member of this group is CH3— CO—CH2—CO—CH3 which is plainly acetyl acetone. It is best made by a reaction exactly analogous to the one used in preparing aceto acetic ester. In making the latter ethy 1 acetate is condensed with itself by means of sodium and ethyl alcohol (sodium ethylate) as described already (p. 254). If instead of condensing with another molecule of itself ethyl acetate condenses with acetone we obtain acetyl acetone, as follows ... 

They can also be used as vinylic carbanion species as shown by the asymmetric synthesis of the chro-man ring of vitamin The (E)/(Z) mixture of chiral sulfoxide (9) was readily isomerized into the ( )-isomer with LDA in THF (the exclusive formation of the ( )-isomer was due to the chelation of lithium with an oxygen of the acetal). Condensation to trimethylhydroquinonecarbaldehyde gave only one diastereoisomer and then the cyclization in presence of sodium methoxide was also fully stereoselective (the stereochemistry of the cyclization being controlled by that of the allylic hydroxy group which is eliminated during the cyclization Scheme 48). 

Condensation with active-methylene compounds. The acetal condenses with cyclopentadiene without solvent at the reflux temperature to give 6-dimethylamino-fulvene (4, m.p. 67°). Similar condensations are reported with acetophenone, malononitrile, nitromethane, ethylacetoacetate. 

In a series of consecutive steps involving 224 and 225 the new polyhetero-cyclic ring system 226 has been made from 223132 (Scheme 58). N-Heteroaromatic enamino esters, such as 227, and ethoxymethylene cyano-acetate condense to afford the vinylenamino ester 228 with hydrazines a 3-aminopyrimidine is annelated (229)1328 (Scheme 59). 

On the other hand the catalyst is of great importance primary, secondary or tertiary amines or their corresponding ammonium salts are usually used, but many other catalysts such as phase transfer catalysts, Lewis acids or potassium fluoride can also be applied. The most widely employed catalysts are pyridine, with or without added piperidine, and ammonium salts, such as ammonium or piperidinium acetate. Condensations that employ strong bases or preformed metal salts of the methylene component are not covered here since transformations under these conditions are not usually considered to be Knoevenagel reactions. 

Diamino-6-methyl-l,3,5-triazine has been shown to react with aldehydes in the presence of potassium hydroxide or methanesulfonic acid <91CPB3I80>. Equation (13) shows a similar type of reaction in which formamide (or lactam) acetals condense with the active methyl group of a 1,3,5-triazinedione <85LA65>. 

Acetal condensations are generally, and most conveniently, conducted at room temperature. Higher temperatures may lead, especially with reducing sugars and their derivatives, to undesirable side-reactions, such as inversion, anhydride formation, and hydrolysis of acid-labile substituents. 

For conducting acetal condensations under very mild conditions, anhydrous copper(II) sulfate alone, or with the addition of a low concentration (0.1-0.25%) of sulfuric acid, has been used. At room temperature, in the absence of acid, the reaction is allowed to proceed for 3 to 10 days. This procedure is most suitable for furanoid derivatives. It should be mentioned that benzyl 8-D-ribofuranoside was acetonated by refluxing with copper(II) sulfate in acetone for 5 hours. Other catalysts that have been employed include phosphorus pentaoxide, anhydrous... 

It has also been suggested that the greater puckering of 2,2-dimethyl-1,3-dioxolane, relative to that of 1,3-dioxolane, would imply that, as less reduction of the dihedral angle of the hydroxyl groups in the diol would be required for the former, the formation of isopropylidene acetals would therefore be easier than that of methylene derivatives. This is confirmed from our knowledge of acetal condensations. 

In addition to the expected 4,6-0-ethylidene acetal, condensation of acetaldehyde with methyl a- or /3-n-glucopyranoside affords a methyl 4,6-0-ethylidene-2,3-0-(oxidodiethylidene)-n-glucopyranoside (26). The seven-... 

In a variant of the above approach, Temple et al. [37c] converted (III. 129) successively to the dichloride (III.134) (72%) and the 2-amino-4(377)-oxo derivative (III.135) (75%). Treatment of (III.135) with acetic anhydride and sulphuric acid followed directly by bromination at 95 °C in acetic acid in the presence of sodium acetate, condensation with 7V-(4-aminobenzoyl)-L-glutamic acid, and alkaline hydrolysis afforded a low yield of (III. 124), whose UV spectral properties (pH 1) 250 nm (e 15,100), 298 (19,400) ... 

Extract sample with ethyl GC/FID/MS acetate condense Inject to GC... 

An alternative procedure substitutes tripiperidinomethane for the DMF acetal. Condensation is done at 110°C with piperidine being removed by distillation at reduced pressure <83TL456i>. tris(Dimethylamino)methane can also be used <8lH(l6)lll9>. The cyclization presumably occurs through an iminium ion derived from the o-aminophenyl enamine. The most commonly used reduction conditions are Raney nickel and hydrazine or hydrogenation over Pd/C. Other reductants which have been used include TiCls <87JA3378> and iron powder with silica in acetic acid <87JHCI499>. 

Synthesis of anti-malarial reagent enpiroline (17) involved the formation of the pyridine skeleton 206 via the Krdhnke reaction of aroyl acrylic acid 204, acyl pyridinium salt 205, and ammonia acetate. Condensation of the carboxyl group in 206 with 2-lithiopyridine afforded the diaryl ketone 207. The relative higher basicity of the terminal pyridinyl ring allowed selective reduction of this ring via hydrogenation in the presence of an acid and simultaneously reduction of the ketone to the alcohol. The desired isomer was then obtained by fractional crystallization to afford 17. ... 

The ammonia, liberated from the ammonium acetate, condenses with the aldehyde, producing an imine. 

In bacteria, most fatty acids have 14 to 20 carbon atoms and are saturated or mono-unsaturated. Lactic acid bacteria also contain a characteristic cyclopropanic acid lactobacillic acid (cw-11,12-methylene-octodecanoic). Table 4.1 lists the principal fatty acids of lactic acid bacteria found in wine—notably Oenococcus oeni (Lonvaud-Funel and Desens, 1990). Malonyl CoA and acetate condense to form fatty acids with an even number of carbon atoms. For an odd number of carbon atoms, fatty acids are synthesized by the condensation of malonyl CoA and propionate. Anaerobic bacteria synthesize unsaturated acids by the action of a dehydratase on hydroxydecanoate which is formed by the addition of a malonyl unit on an octanoic acid molecule. 

According to the present concepts of j3-oxidation and the formation of acetyl CoA, fluoroacetyl CoA should be formed from w-fluoroacetates of an even number of carbons. It has been suggested that fluoro-acetate condenses with another compound, the condensation product being toxic. Since fluorocitrate accumulates in systems poisoned with fluoroacetate, it may be concluded that fluoroacetyl CoA is formed and that it then condenses with oxalacetate. The fact that citrate also accumulates " indicates that either fluoroacetate or fluorocitrate is inhibitory for some step subsequent to the formation of citrate. Cfs-aconitate oxidation is not inhibited therefore, the inhibition appears to be exerted upon the conversion of citrate to cis-aconitate by aconitase. Experimental evidence, as well as theoretical considerations, indicates that fluoroacetate also inhibits fatty acid oxidation by forming complexes with magnesium ions. The apparent association constants of Mg(FAc)+(C i) and Mg(FAc)2(C s) were determined by Gillette and Kalnitsky ... 

Galactarlc acid chloride tetra-acetate, condensed with anthranilic acid followed by dehydration, gave the oxazlnone (8),... 

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