Migration aptitudes and electrical requirements for rearrangement to bivalent carbon

Sargeant, P. B.; Shechter, Harold

doi:10.1016/s0040-4039(01)89348-5

Cited by 17 publications

(4 citation statements)

References 16 publications

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“…Carbene rearrangements involving hydrogen, methyl, or phenyl migration to form olefins have previously been reported by several groups, and the order of migratory aptitude is reported to be H > Ph > Me ) in the thermal decomposition of 2-methyl-2-phenyl-1-diazopropane .…”

Section: Resultsmentioning

confidence: 82%

Mechanistic Study of the Reactions of 1,1-Dihalo-2-methyl-2-phenylpropanes with LDA. Evidence for Radical and Carbene Pathways

1996

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An attempt was made to determine the mechanisms involved in the reactions of the model systems 1,1-dichloro-2-methyl-2-phenylpropane (1) and 1,1-diiodo-2-methyl-2-phenylpropane (2) with LDA. These systems were chosen as ones capable of providing evidence for the formation of radical as well as carbene products. The techniques employed in investigating the mechanistic features of these reactions involved studying the effect of the leaving group, the effect of radical and carbene trapping agents on the product distribution, and isotopic tracer experiments using labeled solvent (THF-d 8) and nucleophile (LDA-d 2). The major product of the reaction of the geminal dichloride (1) is thought to be derived from a chlorocarbene, whereas the geminal diiodide (2) appears to form products derived from both carbene and radical intermediates. On the basis of the results of radical trapping experiments and those of deuterium-labeling experiments, evidence is presented to support the notion that products A, E, and H are derived from a radical precursor. In addition, products A and H are also believed to be formed from the vinylic halide D (or B) and the monoiodide E, respectively. Reasonable mechanisms for the formation of the other products formed in these reactions have been proposed on the basis of the available data.

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Section: Resultsmentioning

confidence: 82%

Mechanistic Study of the Reactions of 1,1-Dihalo-2-methyl-2-phenylpropanes with LDA. Evidence for Radical and Carbene Pathways

1996

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“…On the other hand, D is also expected to readily lose CO to form carbene ( E ), especially under photochemical conditions 23m. The rearrangement from E to benzaldehyde involves a hydrogen migration, and the analogous carbene rearrangement to form olefins has been reported . Attempts to trap E with 2,3-dimethyl-2-butene were unsuccessful.…”

Section: Resultsmentioning

confidence: 99%

Photochemical Reactions of Alkyl Phenylglyoxylates¹

Neckers

1996

J. Org. Chem.

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Three new photoproducts, ethyl O-benzoyl mandelate (5a), ethyl O-acetylmandelate (6a), and biphenyl triketone (7a) are isolated and identified in the reactions of ethyl phenylglyoxylate (1a) in benzene. Quantum yields and initial rate constants of product formation are shown to be concentration dependent. For the formation of carbonyl product 3 at lower starting material concentrations (<0.01 M), quantum yields greater than 1 are observed. Variations in the quantum yields as a function of reaction time are due to the accumulation of alpha-hydroxyphenyl ketene (D). The relative reactivities of triplet excited states of phenylglyoxylates 1 and phenyl ketones are compared. A mechanism involving both intramolecular gamma-H abstraction and intermolecular H abstraction, which leads to radical chain reaction, is proposed. Rate constants for intramolecular gamma-H abstraction (k(N)) and intermolecular H abstraction (k(I)) of methyl phenylglyoxylate (1d) are measured.

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“…This is consistent with the generally accepted rate of migratory aptitude H > Ph > Me, which has been reported from competition studies. [16][17][18] In 1993 Nickon proposed the unconventional view that intrinsic migratory aptitudes for different R groups may be misleading when analyzing carbene rearrangement preferences. He suggested that product ratios are instead frequently determined by the relative abilities of different bystander groups at C 2 to accelerate the reaction.…”

Section: Introductionmentioning

confidence: 99%

Influence of Bystander Substituents on the Rates of 1,2-H and 1,2-Ph Shifts in Singlet and Triplet Carbenes

1998

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Substituent effects at the migration origin on the rate of rearrangement of several alkylchlorocarbenes have been studied at the B3LYP/6-311G**//B3LYP/6-31G* level. Methyl, halo, and phenyl groups are found to accelerate 1,2-H shift rearrangements in the order Ph > Me > F > Cl > H. Methyl groups are also found to accelerate both singlet and triplet 1,2-Ph shifts in benzylchloro- and benzylcarbenes. A direct comparison of the 1,2-H shift in methylchlorocarbene and the 1,2-Ph shift in benzylchlorocarbene shows that the inherent migratory preference of a phenyl group is greater than that of a hydrogen atom. Significant bystander substituent effects are found, as originally proposed by Nickon.

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Migration aptitudes and electrical requirements for rearrangement to bivalent carbon

Cited by 17 publications

References 16 publications

Mechanistic Study of the Reactions of 1,1-Dihalo-2-methyl-2-phenylpropanes with LDA. Evidence for Radical and Carbene Pathways

Mechanistic Study of the Reactions of 1,1-Dihalo-2-methyl-2-phenylpropanes with LDA. Evidence for Radical and Carbene Pathways

Photochemical Reactions of Alkyl Phenylglyoxylates¹

Influence of Bystander Substituents on the Rates of 1,2-H and 1,2-Ph Shifts in Singlet and Triplet Carbenes

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Migration aptitudes and electrical requirements for rearrangement to bivalent carbon

Cited by 17 publications

References 16 publications

Mechanistic Study of the Reactions of 1,1-Dihalo-2-methyl-2-phenylpropanes with LDA. Evidence for Radical and Carbene Pathways

Mechanistic Study of the Reactions of 1,1-Dihalo-2-methyl-2-phenylpropanes with LDA. Evidence for Radical and Carbene Pathways

Photochemical Reactions of Alkyl Phenylglyoxylates1

Influence of Bystander Substituents on the Rates of 1,2-H and 1,2-Ph Shifts in Singlet and Triplet Carbenes

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Photochemical Reactions of Alkyl Phenylglyoxylates¹