An unprecedented rapid and direct bromine(1+) ion transfer from the bromonium ion of adamantylideneadamantane to acceptor olefins

Bennet, Andrew J.; Brown, R. S.; McClung, R. E. D.; Kłobukowski, Mariusz; Aarts, Gerdy H. M.; Santarsiero, Bernard D.; Bellucci, Giuseppe; Bianchini, Roberto

doi:10.1021/ja00022a057

Cited by 50 publications

(21 citation statements)

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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: 99%

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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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Section: Cyclic Bromonium Ion Transfer Between Alkenesmentioning

confidence: 99%

“…Brown and coworkers showed further that nondegenerate translocation of Br þ to cyclohexene and pent-4-enol could be effected to give 43 and 44 respectively by what was deemed to be a diffusion controlled phenomenon [47].…”

Section: Cyclic Bromonium Ion Transfer Between Alkenesmentioning

confidence: 99%

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

Fraser‐Reid¹,

López

2010

Reactivity Tuning in Oligosaccharide Assembly

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“…The reasons behind the difficulty of achieving highly enantioselective halofunctionalization were addressed by the detailed mechanistic investigations by both Brown et al and Denmark et al With the use of 1 H NMR, Brown and co‐workers were able to demonstrate the existence of a rapid and degenerate olefin‐to‐olefin transfer process between free alkenes and bromonium ions (Scheme ) . The rate of this olefin‐to‐olefin transfer process was also found to be kinetically competitive with that of the nucleophilic capture of the bromonium ions.…”

Section: Challenges Of Developing Enantioselective Bromocyclization Omentioning

confidence: 99%

Stereoselective Bromofunctionalization of Alkenes

Tan

Yeung

2013

Chirality

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The stereoselective bromofunctionalization of alkenes, particularly the enantioselective format, has been a subject of intense research in recent years. The ground-breaking works are documented in recent reviews. On the other hand, this account will provide an insight into our group's approach in tackling the challenges in enantioselective bromocyclization of alkenes as well as the development of diastereoselective N-bromosuccinimide-initiated multicomponent reactions.

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“…While the reaction of electron-rich substrate 7b was slow, [11] the reaction of electron-deficient substrate 7cwas efficiently accelerated. [12] Furthermore,t he regioselectivity (13:13' ') was affected by the Lewis base catalysts.T he regioselectivity of the reaction using 5b was different from those without catalyst, or when triethylamine and triphenylphosphine were used as Lewis base catalysts.T hese results suggest that 5b is also involved in the step of lactonization of the bromiranium ion intermediates generated from the substrates. In all cases,only the trans-isomers of dvalerolactones 9 were obtained.…”

mentioning

confidence: 99%

“…First, the bromiranium ion 14 is generated from 5 and 8,a fter which association with another molecule of 5 makes the bromiranium ion shuttle between 14 and 15.T he olefin-to-olefin transfers of the bromiranium ion between two molecules of 5 retard the reaction;t herefore,t he key to increasing the catalytic efficiencyi st he inhibition of the [a] Reactionsw ere run using 7 (0.10 mmol), 8 (0.12 mmol), and 5b (0.010 mmol) in CH 2 Cl 2 (1.0 mL). Bromolactonization of (Z)-5-phenylpent-4-enoic acid (12). Yields in parentheses represent material isolated after silica-gel column chromatography.…”

mentioning

confidence: 99%