Boron‐Catalyzed C−C Functionalization of Allyl Alcohols

Rao, Santhosh; Kapanaiah, Raja; Prabhu, Kandikere Ramaiah

doi:10.1002/adsc.201801389

Cited by 22 publications

(18 citation statements)

References 43 publications

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“…First, B(C 6 F 5 ) 3 coordinates reversibly to the Lewis basic ester on diazo compound 1a , generating the alkene diazonium ion species A , which exists as a mixture of E - and Z -isomers. The proposed O -bound enol diazonium ion is in accord with known values for the equilibrium of C- versus O-bound boron enolates and is predicted to be ∼25 kcal/mol lower in energy than the C -bound isomers . Loss of dinitrogen affords a resonance stabilized Lewis acid-activated carbene intermediate B , which then undergoes a concerted [2 + 1] cycloaddition reaction with the vinyl group on styrene derivative 2a and regenerates the Lewis acid catalyst.…”

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confidence: 80%

Tris(pentafluorophenyl)borane-Catalyzed Cyclopropanation of Styrenes with Aryldiazoacetates

Mancinelli

Wilkerson-Hill

2020

ACS Catal.

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Methods for the synthesis of cyclopropanes are critical for drug discovery, chemical biology, total synthesis, and other fields. Herein, we report the use of the strong sterically encumbered Lewis acid tris(pentafluorophenyl)borane as a catalyst for the cyclopropanation of unactivated alkenes using aryldiazoacetates. The cyclopropane products are synthesized using 10 mol % of the catalyst under mild conditions in up to 90% yield (8:1 to >20:1 dr). We propose that the reaction proceeds via a Lewis acid-activated carbene.

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confidence: 80%

Tris(pentafluorophenyl)borane-Catalyzed Cyclopropanation of Styrenes with Aryldiazoacetates

Mancinelli

Wilkerson-Hill

2020

ACS Catal.

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“…Reaction optimizations showed that B(C 6 F 5 ) 3 was the best catalyst for these transformations. 23 Steric congestion around the boron center (C 6 F 5 substituents) was found to be crucial for product formation, as similar Lewis acidic boranes such as BF 3 ·OEt 2 failed to afford the desired C–C cross-coupled products. Low catalytic loadings (2.5 mol %) with high dilution afforded the best yield of the C–C cross-coupled products, and the formation of competitive O–H insertion reaction (side products) was minimized.…”

Section: C–c Functionalization Reactionsmentioning

confidence: 99%

Triarylborane Catalyzed Carbene Transfer Reactions Using Diazo Precursors

2021

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Reactive carbenes generated from diazo compounds are key intermediates for a range of organic reactions to afford synthetically useful organic compounds. The majority of these reactions have been carried out using transition metal catalysts. However, the formation of carbene intermediates using main group elements has not been widely investigated for synthetic purposes. Recent studies have demonstrated that triarylboranes can be used for the in situ generation of reactive carbene intermediates in both stoichiometric and catalytic reactions. These new reactivities of triarylboranes have gained significant attention in synthetic chemistry particularly in catalytic studies. The range of organic compounds that have been synthesized through these reactions are important as pharmaceuticals or agrochemicals. In this perspective, we highlight the recent progress and ongoing challenges of carbene transfer reactions generated from their corresponding diazo precursors using triarylboranes as catalysts. We also highlight the stoichiometric use of triarylboranes in which the boranes not only activate the diazo functionality to afford a carbene intermediate but also actively participate in the reactions as a reagent. The different mechanisms for activation and carbene transfer are described along with the mechanistic and computational studies that have aided the elucidation of these reaction pathways. Potential opportunities for the use of boranes as a catalyst toward different carbene transfer reactions and their future prospects are discussed.

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“…[3] Recent studies have demonstrated that boranes can be used as an alternative to several transition metal catalysts to activate diazo compounds. [4] In this regard, borane catalyzed carbene transfer has been employed for a range of reactions such as C−H, [5] N−H, [6] O−H [7] insertion, C−C functionalization, [8] carbocycle formation,[ 5a , 9 ] and ring opening reactions. [5a] The efficacy of borane catalysts for carbene transfer reactions has raised our curiosity towards interpreting the mechanism for diazo‐activation.…”

Section: Introductionmentioning

confidence: 99%

Understanding the Influence of Donor‐Acceptor Diazo Compounds on the Catalyst Efficiency of B(C₆F₅)₃ Towards Carbene Formation

Babaahmadi

Dasgupta

Hyland

et al. 2022

Chemistry A European J

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Diazo compounds have been largely used as carbene precursors for carbene transfer reactions in a variety of functionalization reactions. However, the ease of carbene generation from the corresponding diazo compounds depends upon the electron donating/withdrawing substituents either side of the diazo functionality. These groups strongly impact the ease of N2 release. Recently, tris(pentafluorophenyl)borane [B(C6F5)3] has been shown to be an alternative transition metal‐free catalyst for carbene transfer reactions. Herein, a density functional theory (DFT) study on the generation of carbene species from α‐aryl α‐diazocarbonyl compounds using catalytic amounts of B(C6F5)3 is reported. The significant finding is that the efficiency of the catalyst depends directly on the nature of the substituents on both the aryl ring and the carbonyl group of the substrate. In some cases, the boron catalyst has negligible effect on the ease of the carbene formation, while in other cases there is a dramatic reduction in the activation energy of the reaction. This direct dependence is not commonly observed in catalysis and this finding opens the way for intelligent design of this and other similar catalytic reactions.

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Boron‐Catalyzed C−C Functionalization of Allyl Alcohols

Cited by 22 publications

References 43 publications

Tris(pentafluorophenyl)borane-Catalyzed Cyclopropanation of Styrenes with Aryldiazoacetates

Tris(pentafluorophenyl)borane-Catalyzed Cyclopropanation of Styrenes with Aryldiazoacetates

Triarylborane Catalyzed Carbene Transfer Reactions Using Diazo Precursors

Understanding the Influence of Donor‐Acceptor Diazo Compounds on the Catalyst Efficiency of B(C₆F₅)₃ Towards Carbene Formation

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Boron‐Catalyzed C−C Functionalization of Allyl Alcohols

Cited by 22 publications

References 43 publications

Tris(pentafluorophenyl)borane-Catalyzed Cyclopropanation of Styrenes with Aryldiazoacetates

Tris(pentafluorophenyl)borane-Catalyzed Cyclopropanation of Styrenes with Aryldiazoacetates

Triarylborane Catalyzed Carbene Transfer Reactions Using Diazo Precursors

Understanding the Influence of Donor‐Acceptor Diazo Compounds on the Catalyst Efficiency of B(C6F5)3 Towards Carbene Formation

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Understanding the Influence of Donor‐Acceptor Diazo Compounds on the Catalyst Efficiency of B(C₆F₅)₃ Towards Carbene Formation