Transition metal catalyzed reactions of alkynes and boron hydrides: synthesis of 2-(cis-2-butenyl)pentaborane(9) and its conversion into monocarbon carboranes

Wilczynski, Robert; Sneddon, Larry G.

doi:10.1021/ja00528a066

Cited by 48 publications

(17 citation statements)

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“…That transition metals accelerate the addition of B-H bonds to unsaturated organic moieties was initially reported for catalyzed hydroborations of alkenes and alkynes using polyhedral boranes [5][6][7]. Männig and Nöth then demonstrated that rhodium complexes could be used to catalyze the hydroboration of alkenes with HBcat under mild conditions and with chemoselectivity differing from that of the uncatalyzed reaction (Scheme 1) [8].…”

Section: Introductionmentioning

confidence: 98%

Recent Advances in Organic Synthesis Using Transition Metal-Catalyzed Hydroborations

Christopher¹,

Stephen

2005

COC

198

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Among the most significant advances in organic synthesis over the past few decades are those associated with the development of transition metal complexes for their use as catalysts in organic reactions. The discovery that transition metals can also be used to catalyze the addition of B-H bonds to unsaturated substrates has provided the synthetic community with another valuable tool. This review examines recent advances in the field of catalyzed hydroborations and their applications in organic synthesis.R-BR'2 R-CO 2 R" R-R" R-NR"2 R-MLn

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Section: Introductionmentioning

confidence: 98%

Recent Advances in Organic Synthesis Using Transition Metal-Catalyzed Hydroborations

Christopher¹,

Stephen

2005

COC

198

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“…The chemistry of metallaboranes, which are a class of structures that result from the combination of borane cages and metal clusters, has been studied for some time now 7. 8 The reactions of boranes with alkynes lead to carboranes9, 10 that can further incorporate transition‐metal fragments, thereby resulting in the development of metallacarborane chemistry 11–13. In 1974, Grimes et al.…”

Section: Introductionmentioning

confidence: 99%

A Mechanistic Study of the Utilization of arachno‐Diruthenaborane [(Cp*RuCO)₂B₂H₆] as an Active Alkyne‐Cyclotrimerization Catalyst

Geetharani

Tussupbayev

Borowka

et al. 2012

Chemistry A European J

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The reaction of nido-[1,2-(Cp*RuH)(2)B(3)H(7)] (1a, Cp*=η(5)-C(5)Me(5)) with [Mo(CO)(3)(CH(3)CN)(3)] under mild conditions yields the new metallaborane arachno-[(Cp*RuCO)(2)B(2)H(6)] (2). Compound 2 catalyzes the cyclotrimerization of a variety of internal- and terminal alkynes to yield mixtures of 1,3,5- and 1,2,4-substituted benzenes. The reactivities of nido-1a and arachno-2 with alkynes demonstrates that a change in geometry from nido to arachno drives a change in the reaction from alkyne-insertion to catalytic cyclotrimerization, respectively. Density functional calculations have been used to evaluate the reaction pathways of the cyclotrimerization of alkynes catalyzed by compound 2. The reaction involves the formation of a ruthenacyclic intermediate and the subsequent alkyne-insertion step is initiated by a [2+2] cycloaddition between this intermediate and an alkyne. The experimental and quantum-chemical results also show that the stability of the metallacyclic intermediate is strongly dependent on the nature of the substituents that are present on the alkyne.

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“…The results of this study showed that the stereofidelity of the reaction decreased as the amount of triphenylphosphine was increased. This was juxtaposed with an increase in product yield as the phosphine loading was increased from more frugal loadings to the optimized triphenylphosphine-palladium (Ph 3 P-Pd) ratio of 8: 1 Thus, at high loadings of triphenylphosphine, a higher yield was obtained at the expense of the enantiomeric purity of the product. 13 Although the exact values of yield and enantioretention were found to vary slightly with the exclusion of potassium carbonate or the inclusion of trace amounts of water, 17 the trend was consistent over all the examined conditions.…”

Section: Scheme 1 Enantiospecific Suzuki-miyaura Cross-couplingmentioning

confidence: 99%

“…The crude residue was purified by column chromatography (hexanes-EtOAc, 50:1 to 20:1) to provide the product in 70% yield (8.13 mg, 0.035 mmol) as a colorless oil. 1 …”

Section: Rac-1-(styren-4-yl)-1-(4-acetylphenyl)ethane (3aa)mentioning

confidence: 99%

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Highly Chemoselective and Enantiospecific Suzuki-Miyaura Cross-Couplings of Benzylic Organoboronic Esters

et al. 2013

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This paper is dedicated to Professor Scott E. Denmark, with thanks for his mentorship, his dedication to excellence and his extensive contributions to science.Abstract: The use of potassium carbonate in addition to silver oxide is shown to increase the enantiospecificity of the SuzukiMiyaura cross-coupling reaction of chiral secondary benzylic boronic esters. From mechanistic studies, it is shown that the reaction is compatible with Mizoroki-Heck coupling partners, even when they are present in considerable excess. This unique chemoselectivity provides the opportunity to carry out sequential reactions.Since its discovery by Sneddon and Wilczynski 1 over 30 years ago, the metal-catalyzed hydroboration of unsaturated carbon-carbon bonds continues to be a reaction of considerable interest. 2 The ability to transform the boronic ester product into useful substrates is critical for the widespread use of this reaction in synthesis. 3 In 2009, our group reported an important advance in this area, namely the enantiospecific Suzuki-Miyaura cross-coupling of aryl iodides 1 and chiral, enantiopure organoboronic esters 2 (Scheme 1). 4 With the exception of the very specific class of cyclopropyl boronic esters, 5 this constituted the first example of a Suzuki-Miyaura cross-coupling reaction of a secondary chiral organoboronic ester, which occurred without loss of stereochemistry and with complete regiochemical fidelity. 6 Since our report, 4 other examples have appeared from the groups of Molander, 7 Suginome 8 and Hall, 9 whilst secondary allylic boronic ester coupling has been reported by our group, 10 and propargylic couplings by Aggarwal. 11 Scheme 1 Enantiospecific Suzuki-Miyaura cross-couplingIn addition to the high enantiospecificity observed in this important reaction, we also found the reaction to be surprisingly chemoselective. 4 Notably, the linear hydroboration isomer 4, obtained by hydroboration with iridium catalysts, and typically considered to be the more reactive regioisomer, 12 was completely unreactive under our optimized cross-coupling conditions (Scheme 2). Also, while studying the mechanistic details of this reaction, we discovered that in the presence of internal or large amounts of external Heck acceptors, complete selectivity was observed for the Suzuki-Miyaura product 3aa (Scheme 2). 13,14 The exploration of this unique chemoselectivity and the rationale behind it is the subject of this paper. Scheme 2 Chemoselective cross-coupling of secondary boronic ester in the presence of primary boronic ester or Heck acceptor In our initial 2009 report, the Suzuki-Miyaura coupling was shown to proceed with high levels of retention of stereochemistry, although some erosion was observed. 4 Indeed, enantiospecificities in the order of 92% were obtained, leaving room for improvement. During a subsequent screen of conditions, we found that the enantiospecificity was improved markedly when potassium carbonate was used in conjunction with silver oxide as the base (Table 1). 15 Interestingly, these gains in enantiospe...

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Transition metal catalyzed reactions of alkynes and boron hydrides: synthesis of 2-(cis-2-butenyl)pentaborane(9) and its conversion into monocarbon carboranes

Cited by 48 publications

References 1 publication

Recent Advances in Organic Synthesis Using Transition Metal-Catalyzed Hydroborations

Recent Advances in Organic Synthesis Using Transition Metal-Catalyzed Hydroborations

A Mechanistic Study of the Utilization of arachno‐Diruthenaborane [(Cp*RuCO)₂B₂H₆] as an Active Alkyne‐Cyclotrimerization Catalyst

Highly Chemoselective and Enantiospecific Suzuki-Miyaura Cross-Couplings of Benzylic Organoboronic Esters

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Transition metal catalyzed reactions of alkynes and boron hydrides: synthesis of 2-(cis-2-butenyl)pentaborane(9) and its conversion into monocarbon carboranes

Cited by 48 publications

References 1 publication

Recent Advances in Organic Synthesis Using Transition Metal-Catalyzed Hydroborations

Recent Advances in Organic Synthesis Using Transition Metal-Catalyzed Hydroborations

A Mechanistic Study of the Utilization of arachno‐Diruthenaborane [(Cp*RuCO)2B2H6] as an Active Alkyne‐Cyclotrimerization Catalyst

Highly Chemoselective and Enantiospecific Suzuki-Miyaura Cross-Couplings of Benzylic Organoboronic Esters

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A Mechanistic Study of the Utilization of arachno‐Diruthenaborane [(Cp*RuCO)₂B₂H₆] as an Active Alkyne‐Cyclotrimerization Catalyst