Cycloisomerisierung von 1,5‐Eninen über eine 5‐<i>endo</i>‐dig‐ Cyclisierungs‐Protodeborylierungs‐Sequenz mit einem frustrierten Lewis‐Paar als Katalysator

Tamke, Sergej; Qu, Zheng‐Wang; Sitte, Nikolai A.; Flörke, Ülrich; Grimme, Stefan; Paradies, Jan

doi:10.1002/ange.201511921

Cited by 23 publications

(1 citation statement)

References 53 publications

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“…The application of frustrated Lewis pairs (FLP) has grown immensely since their first report to activate molecular hydrogen (H 2 ) in the absence of transition metals . The development of new FLP‐catalyzed reactions is in the focus of contemporary research resulting in spectacular transformations, for example, the activation of strong C−F bonds, cross‐couplings, or cycloisomerizations . However, the fundamental understanding of FLP reactivity with the aim to establish a structure–reactivity relationship is in its infancies.…”

Section: Introductionmentioning

confidence: 99%

Structure–Reactivity Relationship in the Frustrated Lewis Pair (FLP)‐Catalyzed Hydrogenation of Imines

Tussing

Kaupmees

Paradies

2016

Chemistry A European J

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The autoinduced, frustrated Lewis pair (FLP)-catalyzed hydrogenation of 16-benzene-ring substituted N-benzylidene-tert-butylamines with B(2,6-F2 C6 H3 )3 and molecular hydrogen was investigated by kinetic analysis. The pKa values for imines and for the corresponding amines were determined by quantum-mechanical methods and provided a direct proportional relationship. The correlation of the two rate constants k1 (simple catalytic cycle) and k2 (autoinduced catalytic cycle) with pKa difference between imine and amine pairs (ΔpKa ) or Hammett's σ parameter served as useful parameters to establish a structure-reactivity relationship for the FLP-catalyzed hydrogenation of imines.

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Section: Introductionmentioning

confidence: 99%

Structure–Reactivity Relationship in the Frustrated Lewis Pair (FLP)‐Catalyzed Hydrogenation of Imines

Tussing

Kaupmees

Paradies

2016

Chemistry A European J

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(C₆F₅)₃B Catalyzed Chemoselective and ortho‐Selective Substitution of Phenols with α‐Aryl α‐Diazoesters

Shi

et al. 2016

Angewandte Chemie

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The development of an efficient method for the site‐selective substitution of unprotected phenols has long been considered as an attractive but challenging task. Herein, we describe a highly chemo‐ and ortho‐selective substitution reaction of phenols with α‐aryl α‐diazoacetates with commercially available (C6F5)3B as the catalyst. This reaction proceeds under simple and mild conditions with high efficiency, it features a wide substrate scope and can be easily scaled up.

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S_N2 Reactions at Tertiary Carbon Centers in Epoxides

et al. 2017

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Described herein is anovel concept for S N 2reactions at tertiary carbon centers in epoxides without activation of the leaving group.Q uantum chemical calculations show why S N 2 reactions at tertiary carbon centers are proceeding in these systems.T he reaction allows flexible synthesis of 1,3-diol building blocks for natural product synthesis with excellent control of the relative and absolute configurations.Designing novel reactions based on mechanisms which are commonly considered as unfavorable is ac hallenging approach to research in chemistry.I ta llows us to overcome limitations in our mechanistic understanding and lays the basis for the discovery of novel synthetic strategies. S N 2r eactions at tertiary carbon atoms provide an attractive starting point for such as trategy.A sy et, S N 2 reactions at tertiary carbon centers require either destabilization of the cation to be formed for the competing S N 1 reaction, [1, 2] or substrates with very good leaving groups. [3, 4] A recent excellent example is the synthesis of isonitriles from tertiary trifluoroacetates and Me 3 SiCN catalyzed by Sc-(OTf) 3 [5] ,areaction that proceeds by stereoselective trapping of the contact ion-pair.Aslight erosion of the exclusive inversion of configuration was observed, however.T he reaction of epoxides with BF 3 and NaBH 3 CN is conceptually similar. [6] It results in ar ing-opening with hydride as nucleophile at the higher substituted carbon atom with inversion of configuration. Thes trong Lewis acid BF 3 may lead to rearrangements of the epoxide.Herein we report S N 2reactions at tertiary carbon centers of epoxides relying on enforcing af avorable "backside attack" of the nucleophile rather than on activating the leaving group.W ith unsymmetrically substituted epoxides typical S N 2r eactions occur at the less substituted carbon center and not at the more substituted carbon center. With our system, this selectivity is overcome by binding ap ronucleophile to the substrate,w ith subsequent activation of the intermediate formed by ac atalyst. In this manner,t he key feature of S N 2r eactions,t he complete inversion of configuration, is preserved, while side-reactions with activated leaving groups,such as skeletal rearrangements or erosion of stereochemical integrity by cation formation, are avoided.Thereductive opening of Sharpless epoxides [7] affords an efficient approach to the synthetically important 1,3-diol unit. Ther egioselective opening at tertiary centers remains unresolved. Here,w ec hose PhSiH 3 with catalytic amounts of tetrabutylammonium fluoride (TBAF) [8] to realize this goal by epoxide hydrosilylation. [9] This reagent combination does not open simple trisubstituted epoxides.I n1 ,2-disubstituted epoxides,hydroxy substitution is mandatory,asdemonstrated in asynthesis of 1,4-diols by S N 2reaction at secondary carbon centers,and occurs by formation of asilyl ether and activation of the silyl ether by fluoride.Opening of 1, 3,a nd 5 with PhSiH 3 /cat. TBAF results in exclusive formation of 1,3-diols wit...

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Cycloisomerisierung von 1,5‐Eninen über eine 5‐endo‐dig‐ Cyclisierungs‐Protodeborylierungs‐Sequenz mit einem frustrierten Lewis‐Paar als Katalysator

Cited by 23 publications

References 53 publications

Structure–Reactivity Relationship in the Frustrated Lewis Pair (FLP)‐Catalyzed Hydrogenation of Imines

Structure–Reactivity Relationship in the Frustrated Lewis Pair (FLP)‐Catalyzed Hydrogenation of Imines

(C₆F₅)₃B Catalyzed Chemoselective and ortho‐Selective Substitution of Phenols with α‐Aryl α‐Diazoesters

S_N2 Reactions at Tertiary Carbon Centers in Epoxides

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Cycloisomerisierung von 1,5‐Eninen über eine 5‐endo‐dig‐ Cyclisierungs‐Protodeborylierungs‐Sequenz mit einem frustrierten Lewis‐Paar als Katalysator

Cited by 23 publications

References 53 publications

Structure–Reactivity Relationship in the Frustrated Lewis Pair (FLP)‐Catalyzed Hydrogenation of Imines

Structure–Reactivity Relationship in the Frustrated Lewis Pair (FLP)‐Catalyzed Hydrogenation of Imines

(C6F5)3B Catalyzed Chemoselective and ortho‐Selective Substitution of Phenols with α‐Aryl α‐Diazoesters

SN2 Reactions at Tertiary Carbon Centers in Epoxides

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Product

Resources

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(C₆F₅)₃B Catalyzed Chemoselective and ortho‐Selective Substitution of Phenols with α‐Aryl α‐Diazoesters

S_N2 Reactions at Tertiary Carbon Centers in Epoxides