Mechanisms of Grignard reagent addition to ketones

We studied the chemical kinetics of the Grignard reaction between heptylmagnesium bromide and carbon dioxide with a new experimental method utilizing positron emitter C-11 labeled CO 2 . A series of experiments was carried out in the presence of a large excess of heptylmagnesium bromide (C 7 H 15 MgBr ) ca. 1.0 × 10 -4 mol) relative to carbon dioxide (CO 2 ) ca. 1.2 × 10 -8 mol). An empirical scheme was assumed based on the results obtained in experiments at the reaction temperature of 20°C. Differential equations were determined by the scheme. It was possible to calculate rate constant values at each temperature of the reaction (at 10, 20, and 30°C) by fitting the equations to experimental measurements. We obtained the value 1.76 × 10 4 J/mol as the activation energy of the main reaction between C 7 H 15 MgBr and CO 2 from the Arrhenius plot (r 2 ) 0.9986) of the rate constants. The reaction simulated with the equations and the activation energy value were in good agreement with the ones obtained experimentally. The obtained value for the activation energy of the main reaction would be applicable to the more common type of Grignard carboxylation with a large excess of CO 2 .

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“…8 The single electron transfer pathway is interesting in this scheme, because a radical reaction generally has a small activation energy.…”

Section: Discussionmentioning

confidence: 99%

Kinetic Study on the Reaction of Heptylmagnesium Bromide with Carbon Dioxide Using Non-Carrier-Added C-11 Labeled Carbon Dioxide

et al. 1996

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“…However, it had been shown that these mixed alkoxides, in the presence of MgX 2 , immediately underwent redistribution to form monomeric alkoxide and the RMgX. [15] The two Schlenk components R 2 Mg and RMgX can both react with carbonyl groups; it is thus important to discuss the solvent influence on the Schlenk equilibrium in order to ascertain whether a change in diastereoselectivity is due to a change in the quantities of these two different organometallic species. Although the symmetric organomagnesium compound R 2 Mg is much more reactive than the Grignard reagent, the predominant species in diluted Et 2 O solutions (0.1Ϫ0.3 ) is RMgBr, with equilibrium constant values of magnitude 10 2 Ϫ10 3 ; while in THF values of 1Ϫ10 are most common.…”

Section: Discussionmentioning

confidence: 99%

“…Although the symmetric organomagnesium compound R 2 Mg is much more reactive than the Grignard reagent, the predominant species in diluted Et 2 O solutions (0.1Ϫ0.3 ) is RMgBr, with equilibrium constant values of magnitude 10 2 Ϫ10 3 ; while in THF values of 1Ϫ10 are most common. [15,16] Thus, in THF, all species of the Schlenk equilibrium are present in appreciable concentration. In a previous paper, however, we demonstrated that the diastereoselectivity in the addition of MeMgBr to aldehyde 1 was deeply affected by the reaction solvent, while addition of Me 2 Mg to 1 did not show solvent effects.…”

Section: Discussionmentioning

confidence: 99%

Dynamic Solvation Effects in Ethylmagnesium Bromide Addition to (2S)-O-(tert-Butyldimethylsilyl)lactal

et al. 2001

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The diastereofacial selectivity of (2S)-O-(tert-butyldimethylsilyl)lactal towards nucleophilic addition of ethylmagnesium bromide is strongly solvent-dependent. We have shown that solute−solvent interactions occurring in a series of ethers, such as tetrahydrofuran, tetrahydropyran, diethyl ether, dipentyl ether, tert-butyl methyl ether, diisopropyl ether, diisopentyl ether, and anisole, can govern a diastereomeric switch from the anti to the syn isomer. Determination of the temper-

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“…Increased solvation of the cation weakens the attraction between the metal cation and the harder center of the ambident ion permitting attack by the alkylating or acylating agent on the nitrogen. In solvents other than ethyl ether, the Schlenk equilibrium may also be involved (14).…”

Section: The Solventmentioning

confidence: 99%

Pyrrole chemistry. XVI. Acylation of the pyrrolyl ambident anion

Wang¹,

Anderson²

1977

Can. J. Chem.

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. Can. J. Chem. 55, 4103 (1977). An investigation of the acylation of the pyrrolyl ambident anion has been carried out. The results have been rationalized in terms of the 'principle of hard and soft acids and bases.' The metal cation, solvent or complexing agent, halide of the pyrrole Grignard reagent, and temperature were varied. As well, the reactions of acylating agents of the carbonyl, cyanide, and carbimine type with the pyrrole Grignard reagent were studied to determine N/C acylation ratios under the same conditions. Several new products were isolated and identified.

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Mechanisms of Grignard reagent addition to ketones

Cited by 132 publications

References 16 publications

Kinetic Study on the Reaction of Heptylmagnesium Bromide with Carbon Dioxide Using Non-Carrier-Added C-11 Labeled Carbon Dioxide

Kinetic Study on the Reaction of Heptylmagnesium Bromide with Carbon Dioxide Using Non-Carrier-Added C-11 Labeled Carbon Dioxide

Dynamic Solvation Effects in Ethylmagnesium Bromide Addition to (2S)-O-(tert-Butyldimethylsilyl)lactal

Pyrrole chemistry. XVI. Acylation of the pyrrolyl ambident anion

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