Big Chemical Encyclopedia

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

Articles Figures Tables About

Ketene reaction

Ketene is known to be a very active acetylating agent. This reagent reacted with the complex, [(CH3)4N] [Cr(HO-A)2], in acetonitrile solution to produce the diester. However, ketene, which normally reacts with alcohols very quickly, reacted slowly in this case (Table I). In all ketene reactions a large excess of ketene was passed through the solution the critical factor determining yield appears to be the total time of refluxing. [Pg.150]

Another effect to be considered is an inductive effect although the total charge on the complex molecule, [Cr(HO-A)2] , is negative, it is possible that chromium (III) exerts its effect on the free OH group, increasing the acidity of the alcohol proton. Acidic alcohols, such as phenol, may be acetylated readily, so that this does not seem to be a plausible explanation for the very slow ketene reaction. [Pg.152]

On HY, phenylacetate dissociates into phenol and ketene (reaction a). Ortho-hydroxyacetophenone is produced partly by the Fries rearrangement of phenylacetate (intramolecular reaction, reaction b) and by trans-acylation (reaction c) while para-hydroxyacetophenone is exclusively the result of trans-acylation (reaction d). Phenylacetate can also disproportionate into phenol and acetoxyacetophenones (reaction e). Para-acetoxyacetophenone can also be formed through transesterification between para-hydroxyacetophenone and phenylacetate (reaction f).The formation of secondary products like 2-methylchromone and 4-methylcoumarine is consecutive to the formation of... [Pg.520]

Acid Anhydrides Preparation of Acid Anhydrides Ketene Reaction... [Pg.100]

A versatile synthesis of cyclopropanones and closely related derivatives is provided by the diazoalkane-ketene reaction as shown in Scheme 2. Using this method, the parent ketone 2>3> and alkyl-substituted cyclopropanones 1()) have been prepared in yields of 60—90% based upon the concentration of diazoalkaneb) (Table 2). The reaction is rapid at Dry Ice-acetone temperatures and is accompanied by evolution of nitrogen. Although most cyclopropanones are not isolable, dilute solutions of 3 (0.5—0.8 M) may be stored at — 78 °C for several days or at room temperature in the presence of suitable stabilizing agents.15) The hydrate and hemiketal derivatives are readily prepared by the addition of water or alcohols to the solutions of. .2>8>5)... [Pg.79]

Another ketene reaction, the enamine ketene reaction, can also be used for ring enlargement. An application of this reaction is shown in Scheme IV/15, in which the enamine of morpholine and cyclotridecanone IV/95 has been transformed to ( )-muscone (IV/99) [53] [54] [55]. Two moles of ketene -generated in situ from acetylchloride and triethylamine or introduced as gaseous ketene - were condensed step-wise with the enamine IV/95 to form the a-pyrone, IV/97. The yield is low (10-28 %). Base catalyzed hydrolysis of IV/97 gave a mixture of the four isomers, IV/98a to IV/98d, yielding, after catalytic hydrogenation, ( )-muscone (IV/99) [53]. [Pg.66]

Tandem Claisen [3 + 3] ketene reactions using acid chlorides for generating optically active intermediates are described (3). [Pg.375]

In addition to products derived from bis-ketenes, reactions of /7 45) and of diethyl... [Pg.9]

The proposal of Blum et al. ° appears to contradict the results of yet another group of researchers, namely, Daly and co-workers, who used Fourier transform infrared (FTIR) spectroscopy to directly follow the formation of the ketene from the DNQ-sulfonate PAC photolysis in the novolac matrix. Under ambient conditions, they found that the ketene appeared to react quickly with water in the film to form indene carboxylic acid. Under dry conditions, with water excluded, however, the ketene appeared to be quite remarkably stable. Although the above experiments were qualitative in approach, they do indicate that the ketene reaction... [Pg.310]

Stereochemistry, substituent effects and activation parameters of most ketene reactions are consistent with a one-step cycloaddition polar effects of substituents and solvents, as well as the isotope effect, often require, however, that a fair amount of charge separation (that is, unequal bond formation) characterises the transition state. It has been kinetically proved that cycloadditions of enamines to ketenes can also proceed through a dipolar intermediate this is so for the reaction between dimethylketene and N-isobutenylpyrrolidine . In the latter case, the rate coefficient for the formation of the intermediate strongly depends on solvent polarity itacetonuriie/ cyclohexane = 560. Use of the Same criteria used for ketenes (as far as experimental data allow it) in the case of the 1,2-cycloadditions of fluorinated olefins results, instead, in the conclusion that a two-step biradical mechanism is operating. Results for 1,2-cycloaddition of sulfonyl isocyanates to olefins, cases (g) and (h) in Table 17, give indications of dipolar intermediates during the course of these reactions. [Pg.142]

The diazomethane-keten reaction gave no 1,3-dipolar adducts, such as those obtained readily enough from the corresponding thioketen (see Vol. 1, p. 44), even at low temperatures. The 2 1 adduct obtained (165) cannot arise by prior dimerization of the keten, whose jS-lactone dimer (166) reacts to give a y-lactone (167) by methylene insertion at the C—O bond, so that quite different hydrolysis products are obtained (see Scheme 48). ... [Pg.107]

The [2+2] cycloaddition of ketenes with imines to form P-lactams is perhaps the most studied of ketene reactions, and because of the continued search for new drugs continues to attract close attention. The reaction of methylketene with the bis-imine forms the dx-monoadduct as the only observed mono-addition product (Scheme 7.54). [Pg.252]


See other pages where Ketene reaction is mentioned: [Pg.752]    [Pg.989]    [Pg.46]    [Pg.171]    [Pg.318]    [Pg.190]    [Pg.147]    [Pg.752]    [Pg.1101]    [Pg.73]    [Pg.79]    [Pg.81]    [Pg.100]    [Pg.1455]    [Pg.1457]    [Pg.100]    [Pg.61]    [Pg.138]    [Pg.196]    [Pg.263]    [Pg.141]   
See also in sourсe #XX -- [ Pg.182 , Pg.183 ]




SEARCH



Addition reactions of ketenes

Alcohols reaction with ketene complexes

Alcohols, reaction with ketenes

Aldehyde reaction with keten

Aldehydes reaction with ketene acetals

Aldehydes reaction with ketenes

Aldehydes reaction with silyl ketene acetals

Aldol reactions methyl trichlorosilyl ketene acetal

Aldol reactions of ketene acetal

Aldol reactions of silyl ketene acetals

Alkenes reaction geometry with ketenes

Alkenes reaction with ketenes

Boranes, reaction with ketenes

Chiral ammonium ketene enolates reaction

Cycloaddition /reactions silyl ketenes

Cycloaddition reactions ketenes, carbene catalysis

Cycloaddition reactions of ketenes

Cyclopentadiene reaction with ketene

Cyclopropenone, diphenylcycloaddition reactions ketenes, metal catalyzed

Diastereoselective addition reactions chiral silyl ketene acetals

Diazoalkanes reaction with ketene

Diels-Alder reactions ketene equivalents

Elimination reactions ketene-forming

Elimination reactions ketenes from

Enantioselective Mannich Reaction using Silyl Ketene Acetals

Ethers, vinyl reaction with ketene acetals

Hydrazones reaction with ketenes

Imines 2+2] cycloaddition reactions with ketenes

Imines reaction with ketene complexes

Imines reaction with ketenes

Imines, reaction with ketene acetals

Imines, reactions with silyl ketene acetals

Imino esters reaction with silyl ketene acetals

Jiro Tsuji 2 Formation and Reactions of Ketenes Generated via Acylpalladium Derivatives

Keten acetals Diels-Alder reaction with

Ketene 2+1] cycloaddition reactions

Ketene acetals 2 + 2] cycloaddition reactions

Ketene acetals Diels-Alder reactions

Ketene acetals reaction with 1,2,4-triazines

Ketene acetals reaction with epoxides

Ketene acetals reactions with isocyanates

Ketene acetals, bis reaction with imines

Ketene acetals, reactions with amines

Ketene alkyl silyl acetals, reactions

Ketene aminals reactions with isocyanates

Ketene chemistry amine reactions

Ketene chemistry carbonylation reactions

Ketene dithioacetals alkynylsilane cyclization reactions

Ketene dithioacetals, reactions with amine

Ketene forming reactions

Ketene imines, aldol-type reaction

Ketene masked, reaction in Diels-Alder

Ketene radical cation, reactions

Ketene reaction with aldehyde

Ketene reaction with, phosgene

Ketene reactions with nucleophiles

Ketene silyl acetals Mannich reaction

Ketene silyl acetals, aldol reactions, selective

Ketene, acylating reactions

Ketene, acylating reactions anhydrides from

Ketene, acylating reactions dimerization

Ketene, acylating reactions properties

Ketene, reaction with proteins

Ketene-Claisen reactions

Ketene-Cope reactions

Ketene-imine cycloaddition in Bose reaction

Ketene-imine reaction pathway

Ketenes 2 + 2] cycloaddition reactions

Ketenes 2+2]cycloaddition reactions with alkenes

Ketenes Perkin reaction

Ketenes Pummerer reaction

Ketenes addition reaction with enolates

Ketenes as intermediates in acylation reactions

Ketenes carbonyl compound reaction

Ketenes dimerization reactions

Ketenes enolizable, reaction with

Ketenes insertion reactions

Ketenes photochemical reactions

Ketenes reaction with allyl carboxylates

Ketenes reaction with boron reagents

Ketenes reaction with carbonyl compounds

Ketenes reaction with nitriles

Ketenes reaction with, phosgene

Ketenes reactions

Ketenes reactions

Ketenes reactions with azines

Ketenes reactions with dienes

Ketenes reactions with singlet oxygen

Ketenes rhodium enolates, aldol reaction

Ketenes trimerization reactions

Ketenes, cycloaddition reactions benzoquinones

Ketenes, diphenyl cycloaddition reactions

Ketenes, divinylDiels-Alder reactions

Ketenes. reactions with phosphazenes

Lead reaction with ketene

Mannich reaction between ketene silyl

NHC-catalysed Reactions of Ketenes

Nitrones reaction with silyl ketene acetals

Oxygen ketene reaction with

Oxygen reaction with bis-silyl ketene acetals

Pericyclic reactions ketenes

Phosphonium ketene acetals, reactions

Reaction with ketene

Reaction with ketene acetals

Reaction with ketenes

Reaction with silyl ketene acetals

Reactions of Chiral Ammonium Ketene Enolates as Nucleophiles with Different Electrophiles

Reactions of Imines with Ketenes (Staudinger Reaction)

Reactions of Ketenes

Reactions of Ketenes and Alkenes

Reactions of Ketenes and Ketenimines

Reactions with Prochiral Ketenes to give Dissymmetric Allenes

Silyl ketene acetals Mukaiyama aldol reactions

Silyl ketene acetals Mukaiyama reactions

Silyl ketene acetals aldol reactions

Silyl ketene acetals conjugate addition reactions

Silyl ketene acetals diastereoselective addition reactions

Silyl ketene acetals reaction with aldehydes, diastereoselectivity

Silyl ketene acetals reactions with N-silylimines

Silyl ketene acetals, chiral reaction with aldehydes

Silyl ketene acetals, chiral reaction with imines

Silyl ketene acetals, reaction

Silyl ketene acetals, reaction with fluoropropionaldehydes

Silyl ketenes, reactions

Silylamines reaction with ketenes

Stereoselectivity ketene cycloaddition reactions

TEMPO reactions with ketenes

Vinylidene chloride, reaction with sodium 2-methoxyethoxide to yield ketene di acetal

Wolff ketene reaction

Ynamines reaction with ketenes

© 2024 chempedia.info