Amidines as potent nucleophilic organocatalysts for the transfer of electrophilic bromine from N-bromosuccinimide to alkenes

Ahmad, Simon M.; Braddock, D. Christopher; Cansell, Gemma; Hermitage, Stephen A.; Redmond, Joanna M.; White, Andrew J. P.

doi:10.1016/j.tetlet.2007.06.112

Cited by 57 publications

(19 citation statements)

References 16 publications

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“…[*] Dr. K. Murai monoimidazoline catalysts 1 b and 1 c showed that the C 3 -symmetric structure of the catalyst was crucial for good selectivity (Table 1, entries 4 and 5). [10] This interesting trend was similar to that observed in our previous study on the conjugate addition of b-ketoesters to nitroolefins in the presence of 1 a. [8] Next, we optimized the reaction with 1 a.…”

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confidence: 82%

Asymmetric Bromolactonization Catalyzed by a C₃‐Symmetric Chiral Trisimidazoline

et al. 2010

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Halolactonization is one of the fundamental transformations in synthetic organic chemistry. [1] This reaction provides synthetically useful products, which can be employed as synthetic intermediates for divergent transformations. A catalytic asymmetric version of this transformation would be very attractive. However, though a number of attempts to develop catalytic asymmetric halolactonization reactions have been made, [2] and several related enantioselective halocyclizations have been developed, [3] these reactions are still under development. Recently, highly enantioselective halolactonization reactions with organocatalysts were reported. [4] Borhan and co-workers reported an enantioselective chlorolactonization of 4-substituted 4-pentenoic acids in the presence of hydroquinidine 1,4-phthalazinediyl diether ((DHQD) 2 PHAL), [4a] and Tang and co-workers reported an enantioselective bromolactonization of conjugated Z enynes with a bifunctional cinchona-alkaloid catalyst bearing a urea moiety. [4b] However, the former reaction was limited to chlorolactonization; bromo-and iodolactonization were not successful, although Br and I are generally more readily transformed into various functional groups than Cl. The latter reaction is limited to particular substrates, such as conjugated Z enynes. Therefore, the development of a novel efficient method for catalytic asymmetric halolactonization is still important. During the preparation of this manuscript, Veitch and Jacobsen reported a tertiary-amine-catalyzed enantioselective iodolactonization. [5] Herein, we present our study on organocatalytic asymmetric halolactonization. By using the structurally unique C 3 -symmetric trisimidazoline 1 a, we developed a novel asymmetric bromolactonization of 5-substituted 5-hexenoic acids.Our working hypothesis for the development of the enantioselective bromolactonization is shown in Scheme 1. We assumed that if the alkenyl carboxylic acid and an appropriate chiral amine could form an ion pair, a chiral environment would be created. At the same time, the carboxylic acid should be activated. Bromolactonization would then proceed enantioselectively, because the olefin and the two possible bromonium intermediates would be in equilibrium in the presence of the brominating reagent, and the activated carboxylic acid, which would be in a chiral environment, should react preferentially with one of the two bromonium ions. [6] This approach is different from recent successful approaches, which mainly involved the creation of chiral environments around the halo cations. [4,5] The key to this hypothesis was the appropriate choice of a chiral amine that would have a good interaction with carboxylic acids. [7] We envisioned that the C 3 -symmetric trisimidazoline 1 a (Scheme 2), which we developed recently as a new organocatalyst entry, [8] could be suitable for our working hypothesis, because an interesting interaction of the trisimidazoline derived from ethylenediamine with carboxylic acids led to the formation of 1:3 complexes in the fie...

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confidence: 82%

Asymmetric Bromolactonization Catalyzed by a C₃‐Symmetric Chiral Trisimidazoline

et al. 2010

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“…(3)], the first intermolecular NHC-catalyzed hydroacylation of unstrained, rather electron-neutral alkenes. This transformation is remarkable as the organocatalyzed transformation of electron-neutral alkenes such as styrenes is a long-standing challenge in organocatalysis; only some rare examples of organocatalyzed epoxidations [11] and organocatalyzed brominations, [12] and a few examples relying on radical mechanisms have been reported. [13] Recently, we designed a family of novel NHCs bearing a 2,6-dimethoxyphenyl moiety.…”

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NHC‐Catalyzed Hydroacylation of Styrenes

2013

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“…For all of the MCRs described in the above four sections, it was found that the reactions proceeded smoothly without any additional NBS activator. Typically, catalyst (either Lewis base or acid) is required to activate NBS in the electrophilic halogenation process. Since we discovered that the reaction efficiency was highly dependent on the acidity of the nucleophilic partners (sulfonamides and carboxylic acids), we speculated that the acidic partners might act as the activator.…”

Section: Nbs‐initiated Multicomponent Reactions (Mcrs)mentioning

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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Amidines as potent nucleophilic organocatalysts for the transfer of electrophilic bromine from N-bromosuccinimide to alkenes

Cited by 57 publications

References 16 publications

Asymmetric Bromolactonization Catalyzed by a C₃‐Symmetric Chiral Trisimidazoline

Asymmetric Bromolactonization Catalyzed by a C₃‐Symmetric Chiral Trisimidazoline

NHC‐Catalyzed Hydroacylation of Styrenes

Stereoselective Bromofunctionalization of Alkenes

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Amidines as potent nucleophilic organocatalysts for the transfer of electrophilic bromine from N-bromosuccinimide to alkenes

Cited by 57 publications

References 16 publications

Asymmetric Bromolactonization Catalyzed by a C3‐Symmetric Chiral Trisimidazoline

Asymmetric Bromolactonization Catalyzed by a C3‐Symmetric Chiral Trisimidazoline

NHC‐Catalyzed Hydroacylation of Styrenes

Stereoselective Bromofunctionalization of Alkenes

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Product

Resources

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Asymmetric Bromolactonization Catalyzed by a C₃‐Symmetric Chiral Trisimidazoline

Asymmetric Bromolactonization Catalyzed by a C₃‐Symmetric Chiral Trisimidazoline