Influence of charge delocalization on aryl migration in cationic 1,2 shifts

McCall, Michael; Townsend, John Marshall; Bonner, William A.

doi:10.1021/ja00843a023

Cited by 11 publications

(5 citation statements)

References 9 publications

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“…The delocalization of the cationic charge at the migration terminus has been suggested as playing an important role (12,13). From this point of view, the greater charge delocalization in 11 over 12, thus giving a less electrophilic migration terminus and lesser tendency for migration for 11, would also fit the present results.…”

supporting

confidence: 82%

The reaction of cis- and trans-1,2-dianisyl-2-phenylvinyl-2-¹³C bromides with acetic acid and silver acetate

Lee¹,

Oka²

1976

Can. J. Chem.

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The reaction of cis- or trans-1,2-dianisyl-2-phenylvinyl-2-13C bromide with HOAc–AgOAc gave a 1:1 mixture of cis- and trans-1,2-dianisyl-2-phenylvinyl-2-13C acetates with no isotopic scrambling according to pmr and cmr analyses. The lack of degenerate 1,2-phenyl shift in this system is in contrast with the finding of about 7% scrambling in the analogous reaction with triphenylvinyl-2-13C bromide and mechanistic implications of this difference are discussed.

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supporting

confidence: 82%

The reaction of cis- and trans-1,2-dianisyl-2-phenylvinyl-2-¹³C bromides with acetic acid and silver acetate

Lee¹,

Oka²

1976

Can. J. Chem.

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“…In every case the material balance was good. The additional product, 2-(4-methoxyphenyl)-1,2-diphenylethanone, obtained from irradiation of 1c, arose from 1,2-migration of a phenyl group within the cation resulting from the deprotonation of 1c •+ and oxidation of the resulting radical, a process previously observed with similar substrates . There was no significant competitive deprotonation when a C−C or a C−Si benzylic fragmentation occurred, except in the case of cation radical 1e • + in the presence of added nitrate, when deprotonation and C−C bond fragmentation were both observed.…”

Section: Discussionmentioning

confidence: 70%

A Kinetic Evaluation of Carbon−Hydrogen, Carbon−Carbon, and Carbon−Silicon Bond Activation in Benzylic Radical Cations

et al. 1998

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A detailed study of the competition between C−C, C−H, and C−Si bond fragmentation in a series of 4-methoxy-α-substituted toluene radical cations (1 • + ), involving both product studies and kinetic analysis, is presented. C−C bond fragmentation occurs with several radical cations in acetonitrile. The rate constants for such processes, determined by laser flash photolysis, varied from 2.8 × 104 (1c • + ) to 1.53 × 106 (1f • + ) s-1. The activation parameters for C−C bond fragmentation are characterized by low activation enthalpies on the order of 30 kJ mol-1 and negative activation entropies in the range −34 to −55 J mol-1 K-1. Deprotonation of the radical cations is always a second-order process induced by nucleophiles [cerium(IV) ammonium nitrate (CAN) or nitrate anion], with second-order rate constants from 7.7 × 107 (1h • + ) to 8.8 × 108 (1i • + ) M-1 s-1 in neat acetonitrile (CAN assisted) and from 0.4 × 108 (1j • + ) to 7.1 × 108 (1i • + ) M-1 s-1 in the presence of nitrate anion. The rate constant for nitrate-induced decarboxylation was higher, 13.6 × 108 M-1 s-1 (1d • + ). In a few cases C−C (1e • + , 1f • + ) and C−Si (1g • + ) fragmentations occurred, also as second-order processes induced by nitrate, with rate constants from 4.4 × 108 (1f • + ) to 8.2 × 108 (1g • + ) M-1 s-1. ΔH ⧧ and ΔS ⧧ had opposing influences on C−H and C−C fragmentation, and in the case of 1e • + a temperature-dependent product distribution was obtained. The activation parameters for the observed C−H, C−C, and C−Si fragmentations have been compared, and suggest a rationale for the mechanisms and selectivity of such processes in radical cations.

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“…'If the same arguments regarding the stability of trianisyl and triphenyl substituted ions were zpplied to analogous saturated systems, the deainination of I ,2,2-trianisylethylamine should give more rearrangement than the deamination of 1,2,2-triphenylethylamine, but this was not the case (14,15). The present results thus indicate that there are interesting differences between the binylic and saturated analop.…”

mentioning

confidence: 53%

“…Furthermore, Bonner and Putkey (14) have actually observed a lower extent of 1,2-anisyl shift (17%) in the deamination of 1,2,2-trianisylethylamine-1-14C than the previously observed 1,2-phenyl shift (26-28%) in the deamination of 1,2,2-triphenylethylamine-1-14C. A diminished positive character due to the delocalization of the positive charge at the migration terminus has been suggested as playing an important role in accounting for this reversal in migratory aptitudes (14,15). If the reactions of 1 and 2 with acids were to behave in similar ways as the deamination reactions of saturated systems, one would expect that the extent of 1,2-phenyl shift in reactions of 1 should be less than the 1,2-anisyl shift in reactions of 2 by a factor of no more than about two.…”

mentioning

confidence: 85%

Rearrangement studies with ¹⁴C. XLI. Degenerate rearrangements in vinyl cations from triphenylvinyl-2-¹⁴C-phenyltriazene and from trianisylvinyl-2-¹⁴C-phenyltriazene

Lee¹,

Ko²

1976

Can. J. Chem.

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The triphenylvinyl cation generated from reactions of triphenylvinyl-2-14C-phenyltriazene (1) with a number of acids gave no isotopic scrambling from degenerate 1,2-phenyl shifts. The trianisylvinyl cation generated from reaction of trianisylvinyl-2-14C-phenyltriazene (2) with HOAc showed about 38% scrambling of the label from C-2 to C-1, attributable to degenerate 1,2-anisyl shifts. When 2 was treated with HOAc containing 1.7 equiv. of NaOAc, the extent of scrambling was decreased to about 17%. Mechanistic implications of these results are discussed.

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Influence of charge delocalization on aryl migration in cationic 1,2 shifts

Cited by 11 publications

References 9 publications

The reaction of cis- and trans-1,2-dianisyl-2-phenylvinyl-2-¹³C bromides with acetic acid and silver acetate

The reaction of cis- and trans-1,2-dianisyl-2-phenylvinyl-2-¹³C bromides with acetic acid and silver acetate

A Kinetic Evaluation of Carbon−Hydrogen, Carbon−Carbon, and Carbon−Silicon Bond Activation in Benzylic Radical Cations

Rearrangement studies with ¹⁴C. XLI. Degenerate rearrangements in vinyl cations from triphenylvinyl-2-¹⁴C-phenyltriazene and from trianisylvinyl-2-¹⁴C-phenyltriazene

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Influence of charge delocalization on aryl migration in cationic 1,2 shifts

Cited by 11 publications

References 9 publications

The reaction of cis- and trans-1,2-dianisyl-2-phenylvinyl-2-13C bromides with acetic acid and silver acetate

The reaction of cis- and trans-1,2-dianisyl-2-phenylvinyl-2-13C bromides with acetic acid and silver acetate

A Kinetic Evaluation of Carbon−Hydrogen, Carbon−Carbon, and Carbon−Silicon Bond Activation in Benzylic Radical Cations

Rearrangement studies with 14C. XLI. Degenerate rearrangements in vinyl cations from triphenylvinyl-2-14C-phenyltriazene and from trianisylvinyl-2-14C-phenyltriazene

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The reaction of cis- and trans-1,2-dianisyl-2-phenylvinyl-2-¹³C bromides with acetic acid and silver acetate

The reaction of cis- and trans-1,2-dianisyl-2-phenylvinyl-2-¹³C bromides with acetic acid and silver acetate

Rearrangement studies with ¹⁴C. XLI. Degenerate rearrangements in vinyl cations from triphenylvinyl-2-¹⁴C-phenyltriazene and from trianisylvinyl-2-¹⁴C-phenyltriazene