- NEW METHODOLOGY IN DETERMINING EVIDENCE FOR SINGLE ELECTRON TRANSFER IN THE REACTION OF GRIGNARD REAGENTS WITH KETONES
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A new method is reported to determine the existence of single electron transfer in the reaction of Grignard reagents with ketones.The method involves the determination of pseudo-first order rate constants by following the rate of disappearance of the paramagnetic intermediate and relating the rate of this disappearance to the appearance of the product.The reactions of methyl-, phenyl- and t-butyl-Grignard reagents with substituted benzophenones were examined.This method should be applicable to a wide range of organometallic reactions.
- Zhang, Yunshi,Wenderoth, Bernd,Su, Wei-Yang,Ashby, E. C.
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- ELECTRO-ORGANIC REACTIONS. PART 25. THE ROLE OF CHROMIUM(III) IN THE MODIFICATION OF CATHODIC PINACOLISATION
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The presence of chromium(III) chloride, both hydrated and anhydrous, profoundly alters the course of cathodic in dimethylformamide solutions of benzophenone, benzaldehyde, β-ionone, β-ionylidene acetaldehyde, and retinal.Pinacolisation is enhanced at the expense of formation of the corresponding alcohol.Furthermore the relevant reduction potential is lowered.The mechanism of the reaction has been investigated using voltammetric and coulometric experiments combined with a detailed analysis of preparative-scale reductions under a variety of conditions.The stereochemical course of the reactions has also been considered.In total the results provide compelling evidence in favour of the key reducible intermediate being a carbonyl compound-Cr(III) complex which is formed via the corresponding Cr(III) species with homogenous, inner sphere, re-oxidation playing a crucial role.This is contrary to earlier suggestions invoking the participation of electrogenerated Cr(II) as the reductant.
- Sopher, David W.,Utley, James H. P.
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p. 1361 - 1368
(2007/10/02)
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- Organometallic Reaction Mechanisms. 17. Nature of Alkyl Transfer in Reactions of Grignard Reagents with Ketones. Evidence for Radical Intermediates in the Formation of 1,2-Addition Product Involving Tertiary and Primary Grignard Reagents
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When a Grignard reagent reacts with an aromatic ketone, a radical anion-radical cation pair is formed which can collapse to give 1,2-addition product or dissociate to form a radical anion and a free radical within the solvent cage which in turn can collapse to 1,2-addition product or a conjugate addition product or escape the solvent cage to form pinacol.The 1,2-addition products, which form after dissociation of the radical anion-radical cation pair, show free-radical character as indicated by the cyclized 1,2-addition products formed from the reaction of a tertiary Grignard reagent probe with benzophenone in THF and from the reaction of a primary Grignard reagent probe (neooctenyl Grignard reagent) with benzophenone in ether.The 1,6-addition products, which come about after dissociation of the radical anion-radical cation pair, show free-radical character as evidenced by the cyclized 1,6-addition products formed in all of the reactions which involve the tertiary probe Grignard reagent (in all solvents studied) with benzophenone and 2-MBP and also in the reaction of the neooctenyl probe Grignard reagent with 2-MBP.
- Ashby, E. C.,Bowers, Joseph R.
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p. 2242 - 2250
(2007/10/02)
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