Contribution to the chemistry of boron. 150. Competition between adduct and cation formation in reactions between diorganylborane derivatives and pyridine or lutidines

Narula, Chaitanya K.; Noeth, H.

doi:10.1021/ic00210a014

Cited by 65 publications

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“…[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). [15] This result indicates that the borylation reaction proceeded, supported by Lewis acid-base interaction. [4,5] In C À H borylation, pinacolborane and bis(pinacolate)diboron are usually employed as substrates.…”

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confidence: 87%

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

et al. 2013

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“…Out-of-plane displacements of the central iron atom in iron porphyrin complexes have been used as a measure of the coordinating ability of axial ligands [10,11] so it was of interest whether a boron atom, in the naturally domed subphthalocyanine ligand, would respond similarly. Competition between coordinating anions and neutral N-atom donors has been studied in dialkylboreniumlike species, R 2 BL(SO 3 CF 3 ) [12]. The long-term goal of this work is to develop new Lewis acids based on borenium ions [13,14].…”

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confidence: 99%

Synthesis and structure of the coordinatively unsaturated boron subphthalocyanine cation, [B(SubPc)]⁺

Kato

Tham

Boyd

et al. 2006

Heteroatom Chemistry

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“…[17] It is plausible that borenium cations will be active electrophiles in intermolecular borylation, though there have been no definitive examples published to date. [32][33][34] Borenium cations 1 and 2 are therefore highly electrophilic, with a Lewis acidity towards chloride comparable to AlCl 3 , important for applications in electrophilic aromatic substitution where a strong boron electrophile is essential. This is a boron analogue of classic Friedel-Crafts chemistry, and represents an inexpensive methodology for the formation of synthetically desirable pinacol boronate esters under electronic control direct from the parent arene.…”

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“…Multinuclear NMR spectroscopy suggested the formation of [CatB(L)][AlCl 4 ] (L = Et 3 N (1) and L = N,Ndimethyl-p-toluidine (2); Scheme 1) with 11 [29,30] A sharp 27 Al resonance at d = 104 ppm confirmed the formation of [AlCl 4 ] À . [32][33][34] Borenium cations 1 and 2 are therefore highly electrophilic, with a Lewis acidity towards chloride comparable to AlCl 3 , important for applications in electrophilic aromatic substitution where a strong boron electrophile is essential. On cooling to À20 8C new 11 B resonances were resolved; the two major products corresponded to CatBCl and the borenium cation [CatB(Me 2 NTol)] + , whilst a minor resonance was attributed to [CatBCl(Me 2 NTol)].…”

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Pinacol Boronates by Direct Arene Borylation with Borenium Cations

et al. 2011

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Contribution to the chemistry of boron. 150. Competition between adduct and cation formation in reactions between diorganylborane derivatives and pyridine or lutidines

Cited by 65 publications

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

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

Synthesis and structure of the coordinatively unsaturated boron subphthalocyanine cation, [B(SubPc)]⁺

Pinacol Boronates by Direct Arene Borylation with Borenium Cations

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Contribution to the chemistry of boron. 150. Competition between adduct and cation formation in reactions between diorganylborane derivatives and pyridine or lutidines

Cited by 65 publications

References 0 publications

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

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

Synthesis and structure of the coordinatively unsaturated boron subphthalocyanine cation, [B(SubPc)]+

Pinacol Boronates by Direct Arene Borylation with Borenium Cations

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Synthesis and structure of the coordinatively unsaturated boron subphthalocyanine cation, [B(SubPc)]⁺