Fast Ring-Opening of an Intermediary α-Stannyl-β-Cyclopropylvinyl Radical Does Not Support Formation of an α-Stannylvinyl Cation in the O-Directed Free Radical Hydrostannation of Dialkyl Acetylenes

Watson, Hamish A.; Manaviazar, Soraya; Steeds, Hannah G.; Hale, Karl J.

doi:10.26434/chemrxiv.8867651.v1

Cited by 4 publications

(3 citation statements)

References 1 publication

(2 reference statements)

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“…For example, recent mechanistic studies into "classical" reactions involving tin hydrides have revealed fascinating complexity and paved the way to rational development of improved reaction protocols. [14][15][16][17][18][19] The addition of antimony hydrides (primary or secondary stibines) to multiple bondshydrostibination -has been explored to a very limited extent, 20, 21 with well-defined examples being restricted to cases that proceed under Lewis-acid or radical-initiator (azobisisobutyronitrile, AIBN) mediated conditions. 22,23 As part of our exploration into new structure and reactivity at antimony and bismuth centres, 24,25 we recently reported the first definitive catalyst-and additive-free addition of stibines to alkenes, alkynes, ketones, and azobenzene.…”

Section: Introductionmentioning

confidence: 99%

Hydrostibination of Alkynes: A Radical Mechanism**

MacMillan

Marczenko

Johnson

et al. 2020

Chemistry A European J

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The addition of Sb-H bonds to alkynes was reported recently as a new hydroelementation reaction that exclusively yields anti-Markovnikov Z-olefins from terminal acetylenes. We examine four possible mechanisms that are consistent with the observed stereochemical and regiochemical outcomes. A comprehensive analysis of solvent, substituent, isotope, additive, and temperature effects on hydrostibination reaction rates definitively refutes three ionic mechanisms involving closed-shell charged intermediates. Instead the data support a fourth pathway featuring neutral radical Sb II and Sb III intermediates. Density Functional Theory (DFT) calculations are consistent with this model, predicting an activation barrier that is within 1 kcal/mol of the experimental value (Eyring analysis) and a rate limiting step that is congruent with experimental kinetic isotope effect. We therefore conclude that hydrostibination of arylacetylenes is initiated by the generation of stibinyl radicals, which then participate in a cycle featuring Sb II and Sb III intermediates to yield the observed Z-olefins as products. This mechanistic understanding will enable rational evolution of hydrostibination as a methodology for accessing challenging products such as E-olefins.

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Section: Introductionmentioning

confidence: 99%

Hydrostibination of Alkynes: A Radical Mechanism**

MacMillan

Marczenko

Johnson

et al. 2020

Chemistry A European J

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show abstract

“… 88 − 91 Nevertheless, recent publications have started to focus in this transformation for the synthesis of allenes showing carbon-heteroatom bonds, not easily accessible through any other approach. Thus, B-, 92 P-, 93 and Sn-decorated allenols 29 – 31 , 94 − 96 have been synthesized using different transition metals as catalysts and mild reaction conditions ( Scheme 7 ).…”

Section: Synthesis Of Allenolsmentioning

confidence: 99%

Deciphering the Chameleonic Chemistry of Allenols: Breaking the Taboo of a Onetime Esoteric Functionality

2021

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The allene functionality has participated in one of the most exciting voyages in organic chemistry, from chemical curiosities to a recurring building block in modern organic chemistry. In the last decades, a special kind of allene, namely, allenol, has emerged. Allenols, formed by an allene moiety and a hydroxyl functional group with diverse connectivity, have become common building blocks for the synthesis of a wide range of structures and frequent motif in naturally occurring systems. The synergistic effect of the allene and hydroxyl functional groups enables allenols to be considered as a unique and sole functionality exhibiting a special reactivity. This Review summarizes the most significant contributions to the chemistry of allenols that appeared during the past decade, with emphasis on their synthesis, reactivity, and occurrence in natural products.

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“…For example, recent mechanistic studies into "classical" reactions involving tin hydrides have revealed fascinating complexity and paved the way to rational development of improved reaction protocols. [14][15][16][17][18][19] The addition of antimony hydrides (primary or secondary stibines) to multiple bondshydrostibination -has been explored to a very limited extent, 20,21 with well-defined examples being restricted to cases that proceed under Lewis-acid or radical-initiator (azobisisobutyronitrile, AIBN) mediated conditions. 22,23 As part of our exploration into new structure and reactivity at antimony and bismuth centres, 24,25 we recently reported the first definitive catalyst-and additive-free addition of stibines to alkenes, alkynes, ketones, and azobenzene.…”

Section: Introductionmentioning

confidence: 99%

Hydrostibination of Alkynes: A Radical Mechanism

MacMillan¹,

Marczenko²,

Johnson³

et al. 2020

Preprint

View full text Add to dashboard Cite

The addition of Sb-H bonds to alkynes was reported recently as a new hydroelementation reaction that exclusively yields anti-Markovnikov Z-olefins from terminal acetylenes. We examine four possible mechanisms that are consistent with the observed stereochemical and regiochemical outcomes. A comprehensive analysis of solvent, substituent, isotope, additive, and temperature effects on hydrostibination reaction rates definitively refutes three ionic mechanisms involving closed-shell charged intermediates. Instead the data support a fourth pathway featuring neutral radical SbII and SbIII intermediates. Density Functional Theory (DFT) calculations are consistent this model, predicting an activation barrier that is within 1 kcal mol-1 of the experimental value (Eyring analysis) and a rate limiting step that is congruent with experimental kinetic isotope effect. We therefore conclude that hydrostibination of arylacetylenes is initiated by the generation of stibinyl radicals, which then participate in a cycle featuring SbII and SbIII intermediates to yield the observed Z-olefins as products. This mechanistic understanding will enable rational evolution of hydrostibination as a methodology for accessing challenging products such as E-olefins.

show abstract

Fast Ring-Opening of an Intermediary α-Stannyl-β-Cyclopropylvinyl Radical Does Not Support Formation of an α-Stannylvinyl Cation in the O-Directed Free Radical Hydrostannation of Dialkyl Acetylenes

Cited by 4 publications

References 1 publication

Hydrostibination of Alkynes: A Radical Mechanism**

Hydrostibination of Alkynes: A Radical Mechanism**

Deciphering the Chameleonic Chemistry of Allenols: Breaking the Taboo of a Onetime Esoteric Functionality

Hydrostibination of Alkynes: A Radical Mechanism

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