Reactive nitrogen species: Nitrosonium ions in organic synthesis

Bering, Luis; Antonchick, Andrey P.

doi:10.1016/j.tet.2019.01.036

Cited by 18 publications

(13 citation statements)

References 113 publications

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“…The important role of tropylium ion was highlighted by the fact that potassium or tetrabutylammonium salts of the same counterions either showed no catalytic activity or hindered the reaction. Furthermore, other hydride abstractors or organic Lewis acids such as tritylium or nitrosonium salts could also catalyze the reaction but with lower efficiencies than tropylium salts (entry 8). Tritylium salt was previously used in sub-stoichiometric quantities to initiate NHC–borane-mediated hydroboration of alkene via hydride abstraction .…”

Section: Resultsmentioning

confidence: 96%

Tropylium-Promoted Hydroboration Reactions: Mechanistic Insights Via Experimental and Computational Studies

2021

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Hydroboration reaction of alkynes is one of the most synthetically powerful tools to access organoboron compounds, versatile precursors for cross-coupling chemistry. This type of reaction has traditionally been mediated by transition-metal or main group catalysts. Herein, we report a novel method using tropylium salts, typically known as organic oxidants and Lewis acids, to promote the hydroboration reaction of alkynes. A broad range of vinylboranes can be easily accessed via this metal-free protocol. Similar hydroboration reactions of alkenes and epoxides can also be efficiently catalyzed by the same tropylium catalysts. Experimental studies and DFT calculations suggested that the reaction follows an uncommon mechanistic pathway, which is triggered by the hydride abstraction of pinacolborane with tropylium ion. This is followed by a series of in situ counterion-activated substituent exchanges to generate boron intermediates that promote the hydroboration reaction.

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Section: Resultsmentioning

confidence: 96%

Tropylium-Promoted Hydroboration Reactions: Mechanistic Insights Via Experimental and Computational Studies

2021

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“…Nevertheless, very recently, the oxidative rearrangement of aromatic pinacols has attracted renewed interest, being considered as a viable alternative to the classic acid‐catalyzed mechanism. [11], [12] …”

Section: Methodsmentioning

confidence: 99%

Insights into Pinacol Rearrangement: Oxidative versus Acid‐Catalyzed Mechanism

et al. 2021

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Reactions of both diastereomers of 1,2‐bis(4‐methoxyphenyl)cyclohexane‐1,2‐diol (1 d) with tris(2,4‐dibromo‐phenyl)aminium hexachloroantimonate as the oxidant in dichloromethane have been investigated to get evidence on the possibility that a pinacol rearrangement may be oxidatively activated rather than acid‐catalyzed. Relevant to this, we found that in the presence of an excess (4 eq) of oxidant, cis‐1 d afforded the rearrangement product 2,2‐bis(4‐methoxyphenyl)cyclohexanone in large amounts, while trans‐1 d gave exclusively the oxidative cleavage product 1,6‐bis(4‐methoxyphenyl)hexane‐1,6‐dione. Stereospecific implications explaining the reactivity difference between the two diastereomeric radical cation intermediates, cis‐ and trans‐1 d⋅+, are discussed.

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“…The important role of tropylium ion was highlighted by the fact that potassium or tetrabutylammonium salts of the same counterions either showed no catalytic activity or hindered the reaction. Furthermore, other hydride abstractors or organic Lewis acids such as tritylium [14] or nitrosonium [15] salts could also catalyze the reaction but with lower efficiencies than tropylium salts (entry 8). The regioselectivity and stereochemistry of the reaction product was confirmed by comparison to literature data and also by a simple isotope labeling study.…”

Section: Optimization and Substrate Scopementioning

confidence: 99%

Tropylium Salt Promoted Hydroboration Reactions: Mechanistic Insights via Experimental and Computational Studies

Ton¹,

Khanh²,

Nguyên

2021

Preprint

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Hydroboration reaction of alkynes is one of the most synthetically powerful tools to access organoboron compounds, versatile precursors for cross coupling chemistry. This type of reaction has traditionally been mediated by transition metal or main group catalysts. Herein, we report a novel method using tropylium salts, typically known as organic oxidants and Lewis acids, to efficiently promote the hydroboration reaction of alkynes. A broad range of vinylboranes can be easily accessed via this metal-free protocol. Similar hydroboration reactions of alkenes and epoxides can also be efficiently catalyzed by the same tropylium catalysts. Experimental studies and DFT calculations suggested that the reaction follows an uncommon mechanistic paradigm, which is triggered by a hydride abstraction of pinacolborane with tropylium ion. This is followed by a series of <i>in situ</i> counterion-activated substituent exchanges to generate boron intermediates that promote the hydroboration reaction.

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Reactive nitrogen species: Nitrosonium ions in organic synthesis

Abstract: Reactive nitrogen species: nitrosonium ions in organic synthesis

Cited by 18 publications

References 113 publications

Tropylium-Promoted Hydroboration Reactions: Mechanistic Insights Via Experimental and Computational Studies

Tropylium-Promoted Hydroboration Reactions: Mechanistic Insights Via Experimental and Computational Studies

Insights into Pinacol Rearrangement: Oxidative versus Acid‐Catalyzed Mechanism

Tropylium Salt Promoted Hydroboration Reactions: Mechanistic Insights via Experimental and Computational Studies

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