A dynamic NMR investigation of the adamantylideneadamantane/bromine system. Kinetic and thermodynamic evidence for reversible formation of the bromonium ion/Brn- pairs

Bellucci, Giuseppe; Bianchini, Roberto; Chiappe, Cinzia; Ambrosetti, R.; Catalano, Donata; Bennet, Andrew J.; Slebocka‐Tilk, H.; Aarts, Gerdy H. M.; Brown, R. S.

doi:10.1021/jo00064a032

Cited by 23 publications

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“…In chlorinated solvents and at moderate halogen concentrations, this nucleophile normally corresponds to a trihalide species. [3,27] The cationic intermediate can be either a cyclic bromirenium or a b-bromovinyl cation as has been reported by Modena and co-workers (Scheme 2). [9,11] Scheme 2.…”

Section: Resultsmentioning

confidence: 72%

“…[1] Subsequent investigations successfully demonstrated the reversibility of this bromonium ion formation [2] and since then the influence of the nature of the nucleophile on the reaction path has been widely investigated. [3] Recently 1:1 adducts between alkenes and dihalogen molecules have been shown to be p complexes, [4] and during the bromination of another highly congested alkene, tetraneopentylethylene, the participation of a second species, a 2:1 complex between two halogen molecules and an alkene molecule, was observed directly. [5] This experimental work demonstrates that the 2:1 charge-transfer complex must be an intermediate between the p complex I and the charged bromonium ion.…”

Section: Introductionmentioning

confidence: 99%

“…The reaction mixtures were maintained in the dark until colorless and, after solvent removal, analyzed by NMR in CDCl 3 , and eventually by GLC. The concentrations of reagents after mixing are reported in Table 3.…”

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confidence: 99%

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Spectroscopic and Theoretical Investigations of Electrophilic Bromination Reactions of Alkynes: The First Evidence for π Complexes as Reaction Intermediates

et al. 1999

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A bromine ± alkyne p complex (l max 294 nm) of 1:1 stoichiometry has been observed for the first time in the course of the bromination of 1-phenylpropyne by means of a diode-array stopped-flow technique. ); this demonstrates that the complex is actually an essential intermediate on the reaction coordinate. The bromination of a series of nine alkynes has been studied. Bromination reactions with negative apparent activation parameters lead to mixtures of E and Z vinyl dibromides, whereas reactions with positive activation energy yield the E isomers exclusively. The reason for the difference in reactivity of these alkynes compared with structurally similar alkenes most likely lies in the stability of these 1:1 charge-transfer complexes. Usually open arylvinyl cations correspond to the energetically favored product-determining intermediates; bridged bromirenium ions are formed from deactivated alkynes and react to give E isomers. The kinetic effect of alkyl groups and of p-OCH 3 , p-CN, and p-NO 2 substituents at the aryl group on the bromination of arylalkylacetylenes is discussed. Density functional calculations provide insight into the geometries, energies, and bonding of the intermediate 1:1 and 2:1 Br 2 ± acetylene complexes involved. These theoretical investigations demonstrate that the most stable trimolecular Br 2 ± Br 2 ± acetylene adduct possesses a structure very similar to a crystallographically characterized Br 2 ± Br 2 ± alkene species, which can directly yield the ionic products, Br À 3 and vinyl cation, driven by the heterolytic action of a solvent.

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Section: Resultsmentioning

confidence: 72%

Section: Introductionmentioning

confidence: 99%

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Spectroscopic and Theoretical Investigations of Electrophilic Bromination Reactions of Alkynes: The First Evidence for π Complexes as Reaction Intermediates

et al. 1999

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“…But Fig. 3 makes it evident that unhindered alkenes are also candidates, and thus bromonium ion transfer appears to be a hitherto unrecognized phenomenon in the bromination of alkenes [47,49].…”

Section: Cyclic Bromonium Ion Transfer Between Alkenesmentioning

confidence: 98%

Armed–Disarmed Effects in Carbohydrate Chemistry: History, Synthetic and Mechanistic Studies

Fraser‐Reid¹,

López

2010

Reactivity Tuning in Oligosaccharide Assembly

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This chapter begins with an account of the serendipitous events that led to the development of n-pentenyl glycosides (NPGs) as glycosyl donors, followed by the chance events that laid the foundation for the armed-disarmed strategy for oligosaccharide assembly. A key mechanistic issue for this strategy was that, although both armed and disarmed entities could function independently as glycosyl donors, when one was forced to compete with the other for one equivalent of a halonium ion, the disarmed partner was found to function as a glycosyl acceptor. The phenomenon was undoubtedly based on reactivity, but further insight came unexpectedly. Curiosity prompted an examination of how ω-alkenyl glycosides, other than n-pentenyl, would behave. Upon treatment with wet N-bromosuccinimide, allyl, butenyl, and hexenyl glucosides gave bromohydrins, whereas the pentenyl analog underwent oxidative hydrolysis to a hemiacetal. Although the answer was definitive, an in depth comparison of n-pentenyl and n-hexenyl glucosides was carried out which provided evidence in support of the transfer of cyclic bromonium ion between alkenes in a steady-state phenomenon. It was found that for two ω-alkenyl glycosides having a relative reactivity ratio of only 2.6:1, nondegenerate bromonium transfer enabled the faster reacting entity to be converted completely to product, while the slower reacting counterpart was recovered completely. This nuance suggests that in the armed/disarmed coupling, such a nondegenerate steady-state transfer is ultimately responsible for determining how the reactants are relegated to donor or acceptor roles.Development of chemoselective armed/disarmed coupling led to another phase in the sequence of serendipities. During experiments to glycosylate an acceptor diol, it was found that armed and disarmed donor's glycosylated different hydroxyl groups. This observation caused us to embark on studies of regioselective glycosylation. One of these studies showed that it is possible to activate selectively n-pentenyl orthoesters (NPOEs) over other n-pentenyl donors, and that this chemoselective process enables regioselective glycosylation. As a result, reaction partners can be so tuned that glycosylation of an acceptor with nine free hydroxyl groups by an n-pentenyl orthoester donor carrying two free hydroxyl groups is able to furnish a single product in 42% yield. Experiments such as the latter suggest that the donor favors a particular hydroxyl group, and/or that a particular hydroxyl favors the donor. Either option implies that the principle of reciprocal donor acceptor selectivity (RDAS) is in operation.Such examples of regioselective glycosylation provide an alternative to the traditional practice of multiple protection/deprotection events to ensure that the only free hydroxyl group among glycosyl partners is the one to be presented to the donor. By avoiding such protection/deprotections, there can be substantial savings of time and material - as well as nervous anxiety.

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“…This behavior can be used in order to collect direct evidence on the formation of a bromiranium ion also in the vanadium catalyzed two-phase system. It is known that when bromine reacts with ADA a yellow precipitate is formed whose empirical formula and properties are consistent with bromiranium-tribromide molecule, shown in Equation 2: (25)(26)(27) We have accomplished different bromination reactions with ADA. First of all, in order to observe the formation of the bromiranium-tribromide ion in a two-phase reaction, ADA (20 mM) was allowed to react in H 2 0 (2 mL pH ca.l) / CHC1 3 (2 mL) mixture with KBr/KBr0 3 (40 mM / 8 mM), at 25°C, 1000 rpm.…”

Section: Two-phase Bromination Of Adamantylideneadamantanementioning

confidence: 99%

From the Speciation of Peroxovanadium Complexes in Aqueous Solution to the Chemistry of Haloperoxidases

Conte

Furia

Moro

1998

ACS Symposium Series

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A dynamic NMR investigation of the adamantylideneadamantane/bromine system. Kinetic and thermodynamic evidence for reversible formation of the bromonium ion/Brn- pairs

Cited by 23 publications

References 0 publications

Spectroscopic and Theoretical Investigations of Electrophilic Bromination Reactions of Alkynes: The First Evidence for π Complexes as Reaction Intermediates

Spectroscopic and Theoretical Investigations of Electrophilic Bromination Reactions of Alkynes: The First Evidence for π Complexes as Reaction Intermediates

Armed–Disarmed Effects in Carbohydrate Chemistry: History, Synthetic and Mechanistic Studies

From the Speciation of Peroxovanadium Complexes in Aqueous Solution to the Chemistry of Haloperoxidases

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