Synthesis of Pyridine−Borane Complexes via Electrophilic Aromatic Borylation

Ishida, Naoki; Moriya, Taisaku; Goya, Tsuyoshi; Murakami, Masahiro

doi:10.1021/jo101920p

Cited by 190 publications

(151 citation statements)

References 21 publications

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“…120 Thus, treatment of 2-phenylpyridine 303 with 3 equiv of BBr 3 and Et 2 N i Pr as HBr scavenger in dichloromethane gave the cyclic product 307 (89%) at room temperature. The proposed sequence involves formation of a complex 304 and subsequent halide abstraction by the excess BBr 3 to give a transient borenium salt 305 , followed by electrophilic borylation via a Wheland intermediate 306 .…”

Section: Borenium Reagents For C-b Bond Formationmentioning

confidence: 98%

Cationic Tricoordinate Boron Intermediates: Borenium Chemistry from the Organic Perspective

2012

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CONTENTS 1. Introduction 4246 2. History of Borenium Ions: Often Considered, Seldom Confirmed 4247 2.1. Suspected Intermediates in B−N Protonation 4247 2.2. Hypothetical Isomers of Cl 3 B•NHMe 2 4247 2.3. The First Observable Borenium Salt 4247 2.4. Nucleophilic Substitution of X 3 B•NR 3 and Py•BF 2 X 4248 2.5. Aminoborenium Ions, Stabilization by n-Delocalization 4249 3. Recent Developments in the Generation of Observable Borenium Intermediates 4249 3.1. Electrophilic Activation by Protonation or by Lewis Acid Catalysis 4249 3.2. Halide Abstraction by a Halophile 4250 3.3. The Borinium−Borenium Interface: Gas-Phase Oxyborenium Ions 4251 3.4. Borenium Salt Generation by Hydride Abstraction 4251 3 . 4 . 1 . H y d r i d e A b s t r a c t i o n b y T r i s -(pentafluorophenyl)borane 4251 3.4.2. Hydride Abstracton by Trityl Salts 4252 3.4.3. Hydride-Bridged Borenium Salt Dimers 4252 3.5. Borenium Ion Generation by Nucleophilic Addition−Heterolysis 4253 4. Borenium Lewis Acidity vs Structure 4254 4.1. Experimental Evaluation of Lewis Acidity 4254 4.2. Computational Evaluation of Borenium Lewis Acidity 4255 5. Borenium Ions and Stereogenic Boron 4257 5.1. Racemization by Heterolysis 4257 5.2. Asymmetric Memory at Stereogenic Boron 4257 5.3. Chiral Salicylaldimine Boronate Complexes 4258 6. Enantioselective Catalysis and Chiral Borenium Ions 4259 6.1. The Dual Function of Oxazaborolidines in the CBS Reduction 4260 6.2. The Role of Borenium Species in Diels−Alder Catalysis 4261 6.3. Reactivity and Scope of Oxazaborolidine-Derived Diels−Alder Catalysts 4263 6.4. Miscellaneous Uses of Chiral Borenium Lewis Acid Catalysts 4265 7. Miscellaneous Applications of Borenium Lewis Acids 4266 7.1. B−O Activation 4266 7.2. Lewis Acidity and π-Conjugated Borenium Analogues 4267 7.3. π-Conjugated Borenium Analogues as Selective Anion Sensors 4268 7.4. Tricoordinate Boron in Structures Containing Metal Cations 4269 8. Borenium Reagents for C−B Bond Formation 4269 8.1. Borenium Ion Equivalents 4269 8.2. Do Borenium Ions Participate in Hydroboration Chemistry? 4270 8.3. Borenium Equivalents in Electrophilic Aromatic Borylation 4271 8.3.1. Intramolecular Borylation 4271 8.3.2. Intermolecular Borylation 4272 8.3.3. Recent Developments in Muetterties Borylation (BX3 plus Proton Scavenger) 4275 9. Extension of Borenium Chemistry to Neighboring Fields and Unusual Environments 4276 9.1. N-Heterocyclic Carbenes as Stabilizing Ligands for Borenium Salts 4276 9.2. Miscellaneous Related Topics Involving BH Species 4277 10. Summary 4278 Author Information 4279 Corresponding Author 4279 Notes 4279 Biographies 4279 Acknowledgments 4279 References 4279

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Section: Borenium Reagents For C-b Bond Formationmentioning

confidence: 98%

Cationic Tricoordinate Boron Intermediates: Borenium Chemistry from the Organic Perspective

2012

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“…Catalytic turnover proceeded effectively at raised temperatures down to catalyst loadings of 5 mol% HNTf 2 . Since Vedejs and co-worker's seminal report in 2009, a number of other intramolecular borylations have been reported where borocations have been proposed as intermediates; this includes pyridyl- [50][51][52] and phosphinite [53]-directed dehydroborations. In the pyridyl-directed borylation, excess BBr 3 and the hindered base, NEt i Pr 2 , were both essential; the base required either to deprotonate an arenium intermediate if the reaction proceeds by an S E Ar mechanism or sequester HBr to prevent protodeboronation.…”

Section: Intramolecular Electrophilic Aromatic Borylationmentioning

confidence: 99%

Fundamental and Applied Properties of Borocations

Ingleson

2015

Synthesis and Application of Organoboron Compounds

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“…Herein, we report the orthoselective borylation of aromatic C À H bonds with a palladium catalyst using the interaction between a Lewis basic nitrogen and Lewis acidic boron atoms. [10][11][12][13][14] To verify the existence of the Lewis acid-base interaction, the following experiment was carried out: a mixture of 2-phenylpyridine (1 a) and 9-BBN (2 a) in CD 2 Cl 2 was stirred at 25 8C for 24 h, and 11 B NMR analysis of the reaction mixture was then conducted. Until recently, it was difficult to promote transition-metal-catalyzed orthoselective CÀH borylation, but several examples of such transformations have appeared in the last one or two years.…”

mentioning

confidence: 99%

Palladium‐Catalyzed ortho‐Selective CH Borylation of 2‐Phenylpyridine and Its Derivatives at Room Temperature

et al. 2013

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Direct C À H bond transformations have received much attention as ideal and highly efficient methods for the synthesis of useful organic compounds. However, several difficulties remain, in particular the issue of regioselectivity. To solve this problem, directing groups bearing the unshared electron pair of a heteroatom have been used, resulting in dramatic development of the chemistry of C À H bond transformations over the last few decades. [1] The directing group usually acts as a Lewis base to coordinate a transition metal, and thus, the metal center comes close to an appropriate site (a CÀH bond) for the reaction, and subsequent CÀH activation occurs (Scheme 1 a). Herein, we report the orthoselective borylation of aromatic C À H bonds with a palladium catalyst using the interaction between a Lewis basic nitrogen and Lewis acidic boron atoms. [2,3] This is a new concept for the directing group; the group also has an electron pair, but coordinates to a Lewis acidic main-group metal, and a boron atom that also bears a hydrogen atom, which is then converted into a reactive species for C À H activation upon treatment with a transition metal (Scheme 1 b). Until recently, it was difficult to promote transition-metal-catalyzed orthoselective CÀH borylation, but several examples of such transformations have appeared in the last one or two years. [4,5] In C À H borylation, pinacolborane and bis(pinacolate)diboron are usually employed as substrates.[6] Therefore, we initially investigated the reactions between 2-phenylpyridine (1 a) and various borane reagents in the presence of a catalytic amount of several transition metal compounds. However, the desired reaction did not occur at all. [7][8][9] The reason for the low reactivity was thought to be that the Lewis acidity of the borane reagents was not enough to promote the Lewis acidbase interaction between the pyridyl group of 1 a and the boron atom of pinacolborane or bis(pinacolate)diboron. Consequently, 9-borabicyclo[3.3.1]nonane (9-BBN, 2 a) was selected as a promising substrate, because 9-BBN has higher Lewis acidity than pinacolborane and bis(pinacolate)diboron. Treatment of 2-phenylpyridine (1 a) with 9-BBN (2 a) in the presence of a catalytic amount of a palladium salt, Pd(OAc) 2 , in 1,2-dichloroethane at 25 8C for 24 h gave ortho-borylated 2-phenylpyridine 3 a in 87 % yield [Eq. (1)]. [10][11][12][13][14] To verify the existence of the Lewis acid-base interaction, the following experiment was carried out: a mixture of 2-phenylpyridine (1 a) and 9-BBN (2 a) in CD 2 Cl 2 was stirred at 25 8C for 24 h, and 11 B NMR analysis of the reaction mixture was then conducted. As a result, a new signal was observed at 0.3 ppm (vs. 27.7 ppm for 2 a), which is consistent with signals observed for boranes coordinated to pyridine derivatives. [15] This result indicates that the borylation reaction proceeded, supported by Lewis acid-base interaction. Moreover, the reaction proceeded even in the absence of the palladium catalyst at higher temperature (135 8C, 73 %). In this reac...

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Synthesis of Pyridine−Borane Complexes via Electrophilic Aromatic Borylation

Cited by 190 publications

References 21 publications

Cationic Tricoordinate Boron Intermediates: Borenium Chemistry from the Organic Perspective

Cationic Tricoordinate Boron Intermediates: Borenium Chemistry from the Organic Perspective

Fundamental and Applied Properties of Borocations

Palladium‐Catalyzed ortho‐Selective CH Borylation of 2‐Phenylpyridine and Its Derivatives at Room Temperature

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