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Ruasse, Marie-Fran�oise; Lambert, Joseph B.

doi:10.1002/poc.610070302

Cited by 6 publications

(8 citation statements)

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“…Although cis ‐stilbene ( 6b ) reacts faster than its trans ‐isomer ( 7b ), both gave anti ‐addition products, the d,l and meso stereoisomers, respectively, in high yields. These results are indicative of a similar reaction pathway for all of the alkene substrates, whether they involve a bromocarbenium ion, a bridged bromonium ion,18, 38–44 or an alkene‐molecular bromine π ‐complex43 in the product determining step. By contrast, bromination of 6b by a tetralkyphosphonium tribromide ionic liquid using 2 and 4 layer reactors yielded the syn ‐addition product preferentially (but the expected anti ‐addition product for 7b ) 10…”

Section: Resultsmentioning

confidence: 60%

Sequential bromination reactions from beads with methyltriphenylphosphonium tribromide groups

Cristiano

Walls

Weiss

2010

J of Physical Organic Chem

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A reusable bromination reagent based on polystyrene beads with covalently appended methyltriphenylphosphonium tribromide groups has been developed. The results from bromination reactions of several structurally diverse unsaturated substrates with the beads and with solutions of a non‐polymeric model brominating reagent, methyltriphenylphosphonium tribromide, are described. It is shown that the reactions are highly regio‐ and stereo‐selective and can be conducted easily. Copyright © 2010 John Wiley & Sons, Ltd.

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Section: Resultsmentioning

confidence: 60%

Sequential bromination reactions from beads with methyltriphenylphosphonium tribromide groups

Cristiano

Walls

Weiss

2010

J of Physical Organic Chem

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“…In these solvents the reaction generally follows a third‐order rate law (second‐order in Br 2 ). A similar ionic mechanism, in which solvent‐assisted bromine–bromine bond breaking occurs in a 1:1 olefin–Br 2 complex and in which the reaction is first‐order in Br 2 (path b), has been established for bromination at low Br 2 concentration in protic solvents, which provide specific electrophilic solvatation by hydrogen bonding to the leaving bromide ion 2. Depending on olefin structure bromination in nucleophilic solvents, for example, methanol, can occur also through a preassociation mechanism, in which the solvent on one side and bromine on the other side preassociate with the double bond before ionization within a ternary complex to generate a cationic intermediate formed in a sandwich between the leaving bromide and the entering solvent 5…”

Section: Introductionmentioning

confidence: 91%

What is the Nature of the First‐Formed Intermediates in the Electrophilic Halogenation of Alkenes, Alkynes, and Allenes?

Lenoir¹,

Chiappe

2003

Chemistry A European J

104

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The pi complexes first formed as essential intermediates from alkenes, alkynes, and allenes with bromine have been investigated in different solvents by UV-spectroscopy in combination with stopped-flow techniques allowing the determination of the equilibrium constants, K(f). Using alkenes with sterically protected double bonds, such as di-tert-butylstilbene and tetraneopentylethylene, the reaction stops at the stage of the 1:1 and 1:2 pi complex of the alkene with bromine as persistent species in 1,2-dichlorethane as solvent. Calculations by state-of-art ab initio and DFT methods reproduces the experimentally determined thermodynamic values quite well, and reveal the preferred structures and nature of both complexes for ethene, ethyne, and allene. Consideration of the entropy term reveals that complexes are stabilized in solution owing to reduction of the entropy loss by restricted translations and rotation. According to calculations these species are Mulliken-outer-type complexes with no or little charge transfer from bromine to the double or triple bond, respectively. The 1:2 complex has a close structural relationship to the bromonium- or bromirenium ion, which is the subsequent intermediate on the reaction coordinate. Steric influences show a strong effect on the K(f) value, which can be explained by the polarizibility of the parent system. Addition-elimination often occurs. In bromination of adamantylidenadamantane and its derivatives the reaction stops at the stage of the bromonium ion. The effect of various polar groups situated in equatorial homoallyl positions on the stability of corresponding pi complex and bromonium ion has been studied in this series.

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“…Alkynes and prochiral alkenes are most often stereospecifically converted to trans adducts an important class of synthons 1. The relevant mechanisms of electrophilic additions have been studied intensively over the last two decades 2–4. Rather than adding bromine to multiple bonds, bromine reacts with aromatic systems by substitution 5.…”

Section: Introductionmentioning

confidence: 99%

Electrophilic Bromination of Alkenes: Environmental, Health and Safety Aspects of New Alternative Methods

Eissen

Lenoir

2008

Chemistry A European J

102

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More than twenty new alternative methods for bromination of alkenes have been evaluated taking into consideration their resource demands, waste production as well as environmental, health and safety aspects. The cost of bromine and the substances designated to circumvent the application of molecular bromine have also been taken into account. As bromine is only one of several problematic substances being used, its avoidance-by applying bromine supported on solid material or by performing the in situ generation of bromine-does not significantly reduce the technological requirements. On the contrary, the resource demands and amount of waste produced by most new methods are significantly higher compared to the standard methods, especially if the recycling of a carrying agent is not efficient. The method using hydrobromic acid and hydrogen peroxide can be regarded as a competitive alternative to the standard method. The application of certain carrying agents could be interesting, because solvents such as carbon tetrachloride or chloroform used during synthesis could be replaced with less problematic ones during work-up. However, problems associated with these alternatives are not resolved as yet.

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Announcement

Cited by 6 publications

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Sequential bromination reactions from beads with methyltriphenylphosphonium tribromide groups

Sequential bromination reactions from beads with methyltriphenylphosphonium tribromide groups

What is the Nature of the First‐Formed Intermediates in the Electrophilic Halogenation of Alkenes, Alkynes, and Allenes?

Electrophilic Bromination of Alkenes: Environmental, Health and Safety Aspects of New Alternative Methods

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