Enolisation of Simple Carbonyl Compounds and Related Reactions

Toullec, Jean

doi:10.1016/s0065-3160(08)60138-0

Cited by 75 publications

(20 citation statements)

References 224 publications

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“…The rate is independent of Mn(III) concentration, first order in ketone concentration, and accelerated by acetate ion, which suggests that base-catalyzed enolization is the rate-determining step of the reaction. The observation that cyclohexanone 1b reacts 10 times slower than cyclopentanone 1a is consistent with this analysis, since enolization of cyclohexanone is about 10 times slower than enolization of cyclopentanone …”

supporting

confidence: 87%

Mn(III)-Based Oxidative Free-Radical Cyclizations of Unsaturated Ketones

1996

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Mn(III)-based oxidative free-radical cyclization of unsaturated ketones is a versatile synthetic procedure with broad applicability. For example, oxidation of cyclopentanone 1a with 2 equiv of Mn(OAc)(3).2H(2)O and 1 equiv of Cu(OAc)(2).H(2)O in AcOH at 80 degrees C for 1.5 h affords 75% of bicyclo[3.2.1]oct-3-en-8-one 8a and 15% of bicyclo[3.2.1]oct-2-en-8-one 9a. Bridged bicyclic ketones that cannot enolize further are isolated in good yield. Monocyclic beta,gamma-unsaturated ketones that can enolize are oxidized further to give gamma-acetoxy enones. The formation of bicyclo[3.3.1]non-2-en-9-one (57a) in 52% yield from 2-allylcyclohexanone (56a) suggests that kinetically controlled enolization is the rate-determining step in alpha-keto radical formation. A wide variety of examples delineating the scope, limitations, and stereoselectivity of this reaction are presented.

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supporting

confidence: 87%

Mn(III)-Based Oxidative Free-Radical Cyclizations of Unsaturated Ketones

1996

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“…The determination of keto−enol equilibrium constants has been at the center of physical organic studies of keto−enol tautomerism for many years. , Many of the quantitative studies have dealt with β-dicarbonyl compounds, which are commonly enolized to such an extent that both keto and enol forms are present in measurable concentrations at equilibrium.…”

Section: Introductionmentioning

confidence: 99%

Enolization of Benzoylacetone in Aqueous Surfactant Solutions: A Novel Method for Determining Enolization Constants

Iglesias

1996

J. Phys. Chem.

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The keto−enol tautomerism of benzoylacetone (1-phenyl-1,3-butadione) in aqueous acidic solution at 25 °C was investigated by studying the influence of anionic, cationic, and nonionic surfactants in the UV−vis spectra of benzoylacetone. The percentage of the enol tautomer was found to increase abruptly at surfactant concentration above the critical micelle concentration (cmc). A model is proposed to quantitatively interpret the experimental results, which allows for the determination of the enolization constant in water, K E, and in micellar, pseudophases; the binding constant of the enol tautomer to micelles, K s; and the extinction coefficients of the ketonic and enolic forms, ε, of benzoylacetone. The formation of the enolate in the absence and presence of micelles in basic media was also studied. The acidity constants of the enolic, and ketonic, forms of benzoylacetone have been determined.

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“…Indeed, the К t constant changes according to a change in the ratio of rates of the rate determining steps of eno lization and ketonization. 22 In the whole series of N acetonylazoles, steric condi tions for proton elimination in the rate determining step (approach of a base to the protonated form of ketone) remain almost unchanged. However, with an enhance ment of the withdrawing properties of the cycle the proton elimination rate should inrease and the rate of the inverse step should decrease, and as a result, К t increases.…”

Section: Resultsmentioning

confidence: 99%

“…Projection of the anion of 2 dinitromethyl 5 nitrotetr azole potassium salt K 6а on the plane passing through the N(2), C(2), N(12), and N(22).…”

mentioning

confidence: 99%

Mechanism of nitration of nitrogen-containing heterocyclic N-acetonyl derivatives. General approach to the synthesis of N-dinitromethylazoles

et al. 2009

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A general synthetic procedure for the synthesis of N dinitromethyl derivatives of nitrogen containing heterocycles has been developed. The procedure includes the destructive nitration of heterocyclic N acetonyl derivatives of tetrazoles, 1,2,4 and 1,2,3 triazoles, pyrazoles, imid azoles and their bicyclic analogs, as well as imides of carboxylic and sulfonic acids and substitut ed hydrazines with mixtures of sulfuric and nitric acids. The kinetic study of the reaction mechanism was performed using UV and NMR spectroscopy. It was found that the NO 2 groups were sequentially introduced into the methylene fragment by the addition of the nitronium ion to multiple bonds of intermediate enols followed by hydrolysis of the acetyl moiety. The rate and direction of the enolization (due to the CH 2 and CH 3 groups) of the N acetonyl com pounds in sulfuric acid solutions were determined by the study of the deuterium exchange kinetics. The synthesis of the N dinitromethyl compounds is complicated by side reactions, such as the decomposition of intermediate α nitroketone, the nitration of the methyl group in the acetonyl moiety, and the nitration of the dinitromethyl products to trinitromethyl derivatives.Nitration with acidic nitrating mixtures of the active methylene moiety of carbonyl structures (1) to form dini tromethyl compounds (destructive nitration) was studied. 1 It can be assumed that the process proceeds through the formation of dinitromethylene derivatives of carbonyl compounds (1´), whose hydrolysis affords dinitromethyl compounds (2) (Scheme 1). Scheme 1In these works, the nitration conditions were selected empirically without revealing regularities of the reaction and its mechanism, which impedes the optimization of synthesis of dinitromethyl compounds.In the present work, in order to detail processes of destructive nitration of active methylene compounds, 2-9 we studied the mechanism, kinetics, and conditions of this reaction using easily accessible N acetonylazoles 10 as an example. Results and DiscussionWe have earlier 11 studied by 13 С NMR spectroscopy the state of N acetonylazoles in an H 2 SO 4 solution for the lowest basicity tetrazole derivatives. It turned out that on going from solutions in neutral solvents to solutions in concentrated H 2 SO 4 the direct spin spin coupling (SSC) constants ( 1 J C,H ) for the N-CH 2 group and СH cycle increase by 4-5 and 16-18 Hz for 1 and 2 acetonyltet razoles and 5 methyltetrazole analogs, respectively. The same increase in 1 J C,H in neutral media is characteristic of N acetonyltetrazolium salts 4 compared to non quater nized N acetonyltetrazoles 3: these constants for the carbon atoms in the N-CH 2 , N-Me, and C-Me fragments in crease by 4-5 Hz, whereas for the С 5 cycle they increase by 15-20 Hz. 11 It follows from this that the N acetonyl derivatives of tetrazole and 5 methyltetrazole in concen trated H 2 SO 4 are protonated to the nitrogen atom of the cycle. 12 Even in the case of low basicity nitrotetrazole (pK BH + = -9.26), 13 the corresponding ketone is p...

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Enolisation of Simple Carbonyl Compounds and Related Reactions

Cited by 75 publications

References 224 publications

Mn(III)-Based Oxidative Free-Radical Cyclizations of Unsaturated Ketones

Mn(III)-Based Oxidative Free-Radical Cyclizations of Unsaturated Ketones

Enolization of Benzoylacetone in Aqueous Surfactant Solutions: A Novel Method for Determining Enolization Constants

Mechanism of nitration of nitrogen-containing heterocyclic N-acetonyl derivatives. General approach to the synthesis of N-dinitromethylazoles

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