Highly Asymmetric Bromocyclization of Tryptophol: Unexpected Accelerating Effect of DABCO-Derived Bromine Complex

Liu, Huan; Jiang, Guangde; Pan, Xixian; Wan, Xiaolong; Lai, Yisheng; Ma, Dawei; Xie, Weiqing

doi:10.1021/ol5004109

Cited by 86 publications

(26 citation statements)

References 33 publications

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“…48 Later work by the same authors on a closely related bromocyclization found that mixtures of “monocationic” and “tricationic” DABCO-derived “Br + ” salts closely related to 22 and 19 gives optimal performance. 49 …”

Section: Challenges For Stereoselective Catalysismentioning

confidence: 99%

“…[48] Later work by the same authors on ac losely related bromocyclization reveals that mixtures of "monocationic" and "tricationic" DABCOderived "Br + "salts closely related to 22 and 19 gives optimal performance. [49] Taking the "monocationic", DABCO-derived "Br + "salts of type 22 for illustration, one could envisage as olid-liquid phase transfer catalysis process in which ac hiral anion PT catalyst transports amonocationic,amine-bound X 2 complex into the organic phase,where it may undergo reaction with an alkene substrate (Scheme 21). If the Lewis basic nitrogen of the amine remains associated with the electrophilic bromine atom during the alkene addition step, [50] enantiotopic face selection might occur by virtue of the chiral counter anion.…”

Section: Angewandte Reviewsmentioning

confidence: 99%

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Catalytic, Stereoselective Dihalogenation of Alkenes: Challenges and Opportunities

2015

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Although recent years have witnessed significant advances in the development of catalytic, enantioselective halofunctionalizations of alkenes, the related dihalogenation of olefins to afford enantioenriched vicinal dihalide products remains comparatively underdeveloped. However, the growing number of complex natural products bearing halogen atoms at stereogenic centers has underscored this critical gap in the synthetic chemist's arsenal. This Review highlights the selectivity challenges inherent in the design of enantioselective dihalogenation processes, and formulates a mechanism-based classification of alkene dihalogenations, including those that may circumvent the "classical" haliranium (or alkene-dihalogen π-complex) intermediates. A variety of metal and main group halide reagents that have been used for the dichlorination or dibromination of alkenes are discussed, and the proposed mechanisms of these transformations are critically evaluated. AbstractCatalysis of alkene dihalogenation , under different activation modes, with control over both the absolute and relative stereochemical course of dihalogen addition, is one of the most vexing problems in stereoselective synthesis. Dihalogenations that circumvent the "classical" haliranium (or alkene-dihalogen π complex) intermediates provide new and exciting opportunities for catalysis, potentially having broader implications for the design of stereoselective alkene difunctionalizations.

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Section: Challenges For Stereoselective Catalysismentioning

confidence: 99%

Section: Angewandte Reviewsmentioning

confidence: 99%

Catalytic, Stereoselective Dihalogenation of Alkenes: Challenges and Opportunities

2015

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“…[4][5][6] Recently, asymmetric anionic phase-transfer reactions 7,8) have been reported using chiral phosphates with an aziridinium cation 9) and N-haloammonium cations. [10][11][12][13][14][15][16][17][18] …”

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confidence: 99%

Acceleration of Acid-Catalyzed Hydrolysis in a Biphasic System by Sodium Tetracyanocyclopentadienides

Sakai

Bito

Itakura

et al. 2016

CHEMICAL & PHARMACEUTICAL BULLETIN

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The hydrolysis of tert-butyldimethylsilyl L-menthyl ether (3) in a CH 2 Cl 2 -1 M HCl biphasic solvent system was accelerated by the addition of sodium tetracyanocyclopentadienides 1. Particularly, the reaction rate was enhanced using sodium salt 1a-c with a lipophilic substituent on the cyclopentadienide ring. From the results obtained by a triphasic experiment, hydrolysis proceeds via the formation of hydronium ion 2 in the aqueous phase by ion exchange, followed by the transfer of 2 to the CH 2 Cl 2 phase.Key words phase-transfer reaction; hydrolysis; tetracyanocyclopentadienide; acid-catalyzed reaction Phase-transfer reactions have garnered increasing attention in organic chemistry because of their mild, sustainable conditions. 1) Phase-transfer catalysts (PTCs) enhance the reactivity of anionic reagents by forming a lipophilic ion pair, mediating a reaction in the organic phase or at the interface between two phases. Enantioselective phase-transfer reactions catalyzed by chiral quaternary ammonium salts are one of the representative methods for synthesizing optically active molecules.2,3) Anionic PTCs have also been developed for reactions where lipophilic anions enhance the solubility of the reactive cationic species, thereby promoting the reactions. Kobayashi et al. have reported the first anionic phase-transfer reaction using tetrakis(3,5-bis(trifluoromethyl) phenyl) borate (TFPB) anion. [4][5][6] Recently, asymmetric anionic phase-transfer reactions 7,8) have been reported using chiral phosphates with an aziridinium cation 9) and N-haloammonium cations. [10][11][12][13][14][15][16][17][18]

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“…[46] Detailed examination of the reactionc onditions revealed that the readily available DABCO-derived brominating reagent Br3 was the most efficient one when chiral phosphoric acid (R)-[H] 8 -TRIP was employed as the catalyst (Scheme 26). [48] Typically,t he designed C3-brominated furoindoline products 103 could be delivered with satisfactory yields and ee values. Notably,r elatively diminished enantioselectivity was observed with 4-substituted tryptamines and bromination of the indole core also occurred for 4-alkoxy-substituted ones, probably due to the highly electron-rich nature of the substrates.…”

Section: Reactionswith Intramolecular Nucleophilic Trappingmentioning

confidence: 99%

Dearomatization through Halofunctionalization Reactions

Liang

Zheng

You

2016

Chemistry A European J

151

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Recent advances in dearomatization through halofunctionalization reactions are summarized in this Minireview. Two general categories of strategies are currently employed in this field. On one hand, the reaction can be initiated with electrophilic halogenation at an alkyne or alkene moiety. The resulting halonium ion intermediate is then captured by a pendant aromatic ring at the ipso position, affording the dearomatization product. On the other hand, electrophilic halogenation can directly take place at a substituted arene, and the final dearomatization product is furnished by deprotonation or intramolecular nucleophilic trap. Highly enantioselective variants have been realized in the latter case by organocatalysis or transition metal catalysis. By applying these methods, various valuable halogenated polycyclic molecular architectures have been obtained from readily available starting materials.

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Highly Asymmetric Bromocyclization of Tryptophol: Unexpected Accelerating Effect of DABCO-Derived Bromine Complex

Cited by 86 publications

References 33 publications

Catalytic, Stereoselective Dihalogenation of Alkenes: Challenges and Opportunities

Catalytic, Stereoselective Dihalogenation of Alkenes: Challenges and Opportunities

Acceleration of Acid-Catalyzed Hydrolysis in a Biphasic System by Sodium Tetracyanocyclopentadienides

Dearomatization through Halofunctionalization Reactions

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